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LKN/2009 Winter School in Mathematical & Computational Biology
1

Network reconstruction, topology and feasible solution space

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From component to systems biology
Palsson (2000) Nat Biotech 20:649
HT analytical chemistry Integrative analysis
Component biology Systems biology Component view
Time-dependentconcentration
Compute flux
FunctionS+E ↔ X → E+P
Systems view
Steady stateflux map
Neededhomeostasis
Calculate C Calculate k
Reactionnetwork

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E. coli on glycerol
Ibarra et al, Nature 420, 186 - 189 (2002)
Objective Max growth rate on glycerolConstraints Network topology
Steady stateMaximum rates

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Permanence of networks• The permanent feature of life is networks
– Interconnections or links between components define the essence of a living process
• Components have finite turn-over time– Metabolites: ~1 min– mRNA: ~2 hour– Cells: a few years (in human)– Yet, organisms remain essentially identical (if older)
• Kinetics is secondary– Networks are relatively insensitive to kinetics– Kinetics can evolve rapidly to realise network
potential

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Systems biology
Components Gen- Transcript- Prote- Metabol-
Reconstruction of biochemical network (unique!)Systemicannotation
Hypothesisgeneration &testing
Phenotypic space is essentially infinite
In silicomodelling Topology Constraints Dynamics Sensitivity Noise

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Reconstruction• All cellular networks
– Metabolic– Regulatory– Signaling
• are (bio)chemical• The chemical nature is important
– Defines a stoichiometric relationship between components (invariable, integer)
– Defines fundamental constraints for the systems• Thermodynamics: irreversibility and relative rates, maximum concentrations• Mass transfer: maximum rates• Spatial constraints: maximum concentrations, maximum rates
• Chemical networks are readily described by a stoichiometric matrix

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Systemic (2D) annotation
Palsson (2004) Nat Biotech 22:1218

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Reconstruction process• Genome sequence• ORF prediction• Gene annotation
– BLAST, Phylogeny, context
• Pathway reconstruction– Synthesis of all biomass components– Missing genes
• Functional validation– Historical data, phenotype arrays– Metabolomics
• Additional information– Regulation, e.g., array analysis

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Annotation workflow

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Automated model compilation• KEGG: Mus musculus release 46
– Primary: pathway maps• GENE & RN files plus COORD files• Covers 50% of genes in mmu-genome LST file
– Secondary: global files• mmu-enzyme LST file• Less specific EC entries
– Reaction attributes: LIGAND• Reaction & reaction-name LST• Compound names and ID• Reaction-mapformula: reversibility
• UniProtKB: Localisation– Default: cytoplasm

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Manual curation
• Technical (KEGG issues)– Inconsistent compound or reaction labels (network
gaps)– Reactions violating atom conservation
• E.g., DNA + nucleotide = DNA• Generic molecules: R• H2O, H+, redox (difficult to pick up)
– Lumped reactions (e.g., PDH)• Connectivity
– Membrane transporters– Biomass drains

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Network gaps• Visual inspection of KEGG maps
– Good for synthesis pathways– 6 essential reactions identified w/o known gene association– All found in human GSM
• Linear programming– Test generation of each biomass component– 3 reactions w/o gene association found (all had irreversible
counterparts in opposite direction)– 5 reactions mapped to mitochondria but needed in cytosol (3
cytosolic in human GSM)• Literature data
– 43 reactions w/o gene association added– 21 subcellular localisations corrected

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Model overview
Unique gene-reaction associations 4617
Metabolites 2104
Number of genes 1399
Other reactionsReactions w/o gene associationMembrane transportersBiomass reactionsAutocatalytic
5268217
Mapped reactions 1757
Total number of reactionsRxns in mitochondria
2037387

Topology
• S[m,n]–Rows for m metabolites–Columns for reactions

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glc-Dg6pf6pfdpdhapg3p13dpg3pg2pgpeppyrlac-Latpadppih2onadhnadhglc-D[e]lac-D[e]h[e]
Enzyme Protein EC # ReactionHEX Hexokinase hk 2.7.1.1 glc-D + atp -> g6p + adp + h v1PGI1 Phosphoglucose isomerase pgi 5.3.1.9 g6p <-> f6p v2PFKA Phosphofructokinase pfkA 2.7.1.11 f6p + atp -> fdp + adp + h v3FBA Fructose-1,6-bisphosphatate aldolase fba 4.1.2.13 fdp <-> dhap + g3p v4TPIA Triosphosphate Isomerase tpiA 5.3.1.1 dhap <-> g3p v5GAPA G3P dehydrogenase-A complex gapA 1.2.1.12 g3p + pi + nad <-> 13dpg + nadh + h v6PGK Phosphoglycerate kinase pgk 2.7.2.3 13dpg + adp <-> 3pg + atp v7GPMA Phosphoglycerate mutase 1 gpmA 5.4.2.1 3pg <-> 2pg v8ENO Enolase eno 4.2.1.11 2pg <-> pep + h2o v9PYKF Pyruvate Kinase I pykF 2.7.1.40 pep + adp + h -> pyr + atp v10LDH_L L-Lactate dehydrogenase Ldh 1.1.1.28 pyr + nadh + h <-> lac-L + nad v11
ATP hydrolysis atp + h2o -> adp + pi + h v12GLCt glucose exchange glc-D[e] <-> glc-D b1L-LAC-t lactate transport lac-L + h <-> h[e] + lac-L[e] b2

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Reaction S' glc-
D
g6p
f6p
fdp
dhap
g3p
13dp
g
3pg
2pg
pep
pyr
lac-
L
atp
adp
pi h2o
nadh
nad
h glc-
D[e
]
lac-
D[e
]
h[e]
glc-D + atp -> g6p + adp + h v1 -1 1 -1 1 1g6p <-> f6p v2 -1 1f6p + atp -> fdp + adp + h v3 -1 1 -1 1 1fdp <-> dhap + g3p v4 -1 1 1dhap <-> g3p v5 -1 1g3p + pi + nad <-> 13dpg + nadh + h v6 -1 1 -1 1 -1 113dpg + adp <-> 3pg + atp v7 -1 1 1 -13pg <-> 2pg v8 -1 12pg <-> pep + h2o v9 -1 1 1pep + adp + h -> pyr + atp v10 -1 1 1 -1 -1pyr + nadh + h <-> lac-L + nad v11 -1 1 -1 1 -1atp + h2o -> adp + pi + h v12 -1 1 1 -1 1glc-D[e] <-> glc-D b1 1 -1lac-L + h <-> h[e] + lac-L[e] b2 -1 -1 1 1

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S v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 b1 b2glc-D -1 1g6p 1 -1f6p 1 -1fdp 1 -1dhap 1 -1g3p 1 1 -113dpg 1 -13pg 1 -12pg 1 -1pep 1 -1pyr 1 -1lac-L 1 -1atp -1 -1 1 1 -1adp 1 1 -1 -1 1pi -1 1h2o 1 -1nadh 1 -1nad -1 1h 1 1 1 -1 -1 1 -1glc-D[e] -1lac-D[e] 1h[e] 1

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Stot, Sexch, Sint
Stot
Prim
ary
Sec
onda
ryE
xter
nal
Internal fluxes Exchange

v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 b1 b2glc-D -1 1g6p 1 -1f6p 1 -1fdp 1 -1dhap 1 -1g3p 1 1 -113dpg 1 -13pg 1 -12pg 1 -1pep 1 -1pyr 1 -1lac-L 1 -1atp -1 -1 1 1 -1adp 1 1 -1 -1 1pi -1 1h2o 1 -1nadh 1 -1nad -1 1h 1 1 1 -1 -1 1 -1glc-D[e] -1lac-L[e] 1h[e] 1
glc-D[e]
glc-D
g6p
f6p
fdp
dhap g3p
13dpg
3pg
2pg
pep
pyr
lac-L
lac-L[e]
Stot

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Stot, Sexch, Sint
Stot
Prim
ary
Sec
onda
ryE
xter
nal
Internal fluxes Exchange
Sexch

Sexchv1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 b1 b2
glc-D -1 1g6p 1 -1f6p 1 -1fdp 1 -1dhap 1 -1g3p 1 1 -113dpg 1 -13pg 1 -12pg 1 -1pep 1 -1pyr 1 -1lac-L 1 -1atp -1 -1 1 1 -1adp 1 1 -1 -1 1pi -1 1h2o 1 -1nadh 1 -1nad -1 1h 1 1 1 -1 -1 1 -1glc-D[e] -1lac-L[e] 1h[e] 1
glc-D[e]
glc-D
g6p
f6p
fdp
dhap g3p
13dpg
3pg
2pg
pep
pyr
lac-L
lac-L[e]

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Stot, Sexch, Sint
Stot
Prim
ary
Sec
onda
ryE
xter
nal
Internal fluxes Exchange
SexchSint

Sintv1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 b1 b2
glc-D -1 1g6p 1 -1f6p 1 -1fdp 1 -1dhap 1 -1g3p 1 1 -113dpg 1 -13pg 1 -12pg 1 -1pep 1 -1pyr 1 -1lac-L 1 -1atp -1 -1 1 1 -1adp 1 1 -1 -1 1pi -1 1h2o 1 -1nadh 1 -1nad -1 1h 1 1 1 -1 -1 1 -1glc-D[e] -1lac-D[e] 1h[e] 1
glc-D[e]
glc-D
g6p
f6p
fdp
dhap g3p
13dpg
3pg
2pg
pep
pyr
lac-L
lac-L[e]

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Reaction map: SMetabolites are nodesFor reaction draw edge between substrates (- entry) to products (+entry)
Highly non-linear mapParticipation: 4 is typical

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Compound map: -ST
• Reaction as nodes• Compounds as links• Connectivity number
– 2 is common– High for ATP etc
• Soft link– metabolites flowing
through reactions not fixed by stoichiometry

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Open or closed systemsA
BC
v1
A
BC
v1
v1
A
B
C
b1
b2
b3 v1
A
B
Cb1
b2
b3
A
BC
v1
b1
b2
b3v1
A
B
Cb1
b2
b3
Ae
Be
Ce
Ae
Ce
Be
Sint
Sexch
Stot

Binary S
S v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 b1 b2 Sb v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 b1 b2glc-D -1 1 glc-D 1 0 0 0 0 0 0 0 0 0 0 0 1 0g6p 1 -1 g6p 1 1 0 0 0 0 0 0 0 0 0 0 0 0f6p 1 -1 f6p 0 1 1 0 0 0 0 0 0 0 0 0 0 0fdp 1 -1 fdp 0 0 1 1 0 0 0 0 0 0 0 0 0 0dhap 1 -1 dhap 0 0 0 1 1 0 0 0 0 0 0 0 0 0g3p 1 1 -1 g3p 0 0 0 1 1 1 0 0 0 0 0 0 0 013dpg 1 -1 13dpg 0 0 0 0 0 1 1 0 0 0 0 0 0 03pg 1 -1 3pg 0 0 0 0 0 0 1 1 0 0 0 0 0 02pg 1 -1 2pg 0 0 0 0 0 0 0 1 1 0 0 0 0 0pep 1 -1 pep 0 0 0 0 0 0 0 0 1 1 0 0 0 0pyr 1 -1 pyr 0 0 0 0 0 0 0 0 0 1 1 0 0 0lac-L 1 -1 lac-L 0 0 0 0 0 0 0 0 0 0 1 0 0 1atp -1 -1 1 1 -1 atp 1 0 1 0 0 0 1 0 0 1 0 1 0 0adp 1 1 -1 -1 1 adp 1 0 1 0 0 0 1 0 0 1 0 1 0 0pi -1 1 pi 0 0 0 0 0 1 0 0 0 0 0 1 0 0h2o 1 -1 h2o 0 0 0 0 0 0 0 0 1 0 0 1 0 0nadh 1 -1 nadh 0 0 0 0 0 1 0 0 0 0 1 0 0 0nad -1 1 nad 0 0 0 0 0 1 0 0 0 0 1 0 0 0h 1 1 1 -1 -1 1 -1 h 1 0 1 0 0 1 0 0 0 1 1 1 0 1glc-D[e] -1 glc-D[e] 0 0 0 0 0 0 0 0 0 0 0 0 1 0lac-L[e] 1 lac-L[e] 0 0 0 0 0 0 0 0 0 0 0 0 0 1h[e] 1 h[e] 0 0 0 0 0 0 0 0 0 0 0 0 0 1
⎭⎬⎫
⎩⎨⎧
≠===
0 if1ˆ0 if0ˆ
:ˆijij
ijij
ssss
S Binary S

Reaction adjacency matrix,
ik
kik
kiiTii ssdiag π===⋅= ∑∑ ˆˆˆˆ)( 2ssAv
πi = participation number for reaction i, i.e., number of compounds participating in reaction i. Off-diagonal elements indicates how many compounds two reactions i and j have in common
Av=Sb'Sb v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 b1 b2v1 5 1 3 0 0 1 2 0 0 3 1 3 1 1v2 1 2 1 0 0 0 0 0 0 0 0 0 0 0v3 3 1 5 1 0 1 2 0 0 3 1 3 0 1v4 0 0 1 3 2 1 0 0 0 0 0 0 0 0v5 0 0 0 2 2 1 0 0 0 0 0 0 0 0v6 1 0 1 1 1 6 1 0 0 1 3 2 0 1v7 2 0 2 0 0 1 4 1 0 2 0 2 0 0v8 0 0 0 0 0 0 1 2 1 0 0 0 0 0v9 0 0 0 0 0 0 0 1 3 1 0 1 0 0v10 3 0 3 0 0 1 2 0 1 5 2 3 0 1v11 1 0 1 0 0 3 0 0 0 2 5 1 0 2v12 3 0 3 0 0 2 2 0 1 3 1 5 0 1b1 1 0 0 0 0 0 0 0 0 0 0 0 2 0b2 1 0 1 0 0 1 0 0 0 1 2 1 0 4
SSAvˆˆ T=

Compound adjacency matrix,
ik
ikk
ikii ss ρ=== ∑∑ ˆˆ)( 2xa
ρi = connectivity number for compound i, i.e., number of reactions in which compound i participates. Off-diagonal elements indicates how many reactions both compounds i and j participate in.
TSSAxˆˆ=
Ax=SbSb' glc-
D
g6p
f6p
fdp
dhap
g3p
13dp
g
3pg
2pg
pep
pyr
lac-
L
atp
adp
pi h2o
nadh
nad
h glc-
D[e
]
lac-
L[e]
h[e]
glc-D 2 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 1 1 0 0g6p 1 2 1 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0f6p 0 1 2 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0fdp 0 0 1 2 1 1 0 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0dhap 0 0 0 1 2 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0g3p 0 0 0 1 2 3 1 0 0 0 0 0 0 0 1 0 1 1 1 0 0 013dpg 0 0 0 0 0 1 2 1 0 0 0 0 1 1 1 0 1 1 1 0 0 03pg 0 0 0 0 0 0 1 2 1 0 0 0 1 1 0 0 0 0 0 0 0 02pg 0 0 0 0 0 0 0 1 2 1 0 0 0 0 0 1 0 0 0 0 0 0pep 0 0 0 0 0 0 0 0 1 2 1 0 1 1 0 1 0 0 1 0 0 0pyr 0 0 0 0 0 0 0 0 0 1 2 1 1 1 0 0 1 1 2 0 0 0lac-L 0 0 0 0 0 0 0 0 0 0 1 2 0 0 0 0 1 1 2 0 1 1atp 1 1 1 1 0 0 1 1 0 1 1 0 5 5 1 1 0 0 4 0 0 0adp 1 1 1 1 0 0 1 1 0 1 1 0 5 5 1 1 0 0 4 0 0 0pi 0 0 0 0 0 1 1 0 0 0 0 0 1 1 2 1 1 1 2 0 0 0h2o 0 0 0 0 0 0 0 0 1 1 0 0 1 1 1 2 0 0 1 0 0 0nadh 0 0 0 0 0 1 1 0 0 0 1 1 0 0 1 0 2 2 2 0 0 0nad 0 0 0 0 0 1 1 0 0 0 1 1 0 0 1 0 2 2 2 0 0 0h 1 1 1 1 0 1 1 0 0 1 2 2 4 4 2 1 2 2 7 0 1 1glc-D[e] 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0lac-L[e] 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 1 1h[e] 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 1 1

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Singletons

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Network topology

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Active, essential and zero-flux reactions
• 950 singletons of 2104 metabolites– Minor biomass components (e.g., spermidine)– “C-unconnected”, e.g., xenobiotics– Annotation errors
• 987 reactions linked to singletons (dead-end metabolites)
• 1050 active (i.e., non-zero flux) reactions– Approximately 270 essential– 409 degrees of freedom

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S as a linear transformation
( ) ( )
DomainRange
balance) mass (Dynamic
],[
2121
mn
kkik
i
Tm
Tn
dtd
dtd
vsdtdx
xxxvvv
nm ℜ∈⎯⎯ →⎯ℜ∈
=
=
==
∑
xv
Svx
xv
S
KK

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Four fundamental spaces
Row(S)
Null(S)
Col(S)
Left null(S)
vdyn
vss
v dx/dt
ℜn ℜm
S[m,n]

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Dimensions of subspaces
• r = Rank(S) = # linearly, independent relationships between compounds and reactions
• dim(Col(S)) = dim(Row(S)) = r• dim(Right null(S)) = n – r• dim(Left null(S)) = m – r

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(Right) null space
• v = vss + vdyn, where Svss=0• vss is in (right) null space of S• Null(S) contains all allowable steady-state
flux distributions.

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Row space
• Together vss + vdyn span ℜn
• vdyn orthogonal to null space, i.e., in row(S)• row(S) contains all dynamic flux
distributions, i.e., the thermodynamic driving forces that changes state

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Column space
• dx/dt = s1v1 + s2v2 …+ snvn, where– si is the ith column in S
• Hence, dx/dt is in the column space of S• Contains all allowable time derivatives of
the concentrations vector and hence how the thermodynamic driving forces move concentration state of network

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Left column space
• Together Left null(S) and Row(S) span ℜm
– Dim(Left null(S)) + Dim(Col(S)) = m• Vectors in the left null space of S are
orthogonal to Col(S)• Left null(S) contains all the conservation
relationships, i.e., time invariants, defined by the network. This defines conserved metabolic pools as combinations of metabolites.

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Four fundamental spaces
Row(S)
Null(S)
Col(S)
Left null(S)
vdyn
vss
v dx/dt
ℜn ℜm
S[m,n]

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Basis for vector spaces• A basis for a space is a set of
vectors that can be used to span the space, e.g.,– b1=(1,0,0), b2=(0,1,0) and
b3=(0,0,1)– Any vector v ∈ ℜ(3) can be
decomposed as– v = w1b1 + w2b2 + w3b3– So [b1,b2,b3] is a basis for ℜ(3)
• Many types of bases– Linear basis– Orthonormal (linear) basis for
linear spaces– Convex basis for finite linear
spaces
x
y
z
(w1,w2,w3)
b1
b2
b3

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Singular value decomposition
[ ] [ ] [ ] [ ]TVΣUS nnnmmmnm ,,,, =
• U and V are orthonormal matrices– UTU = I(mxm) and VTV = I(nxn)
– UT = U-1 and VT = V-1
• Σ = diag(σ1, σ2,…, σr), where σ1≥ σ2 ≥,…, ≥ σr>0

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Orthonormal bases for subspaces
Col(S)Left
null(S)
Row(S)
Null(S)
U VT
rxr
mxn
=
S Σ
Columns in U defines orthonormal basis for Col(S) and Left null(S)Columns in V defines orthonormal basis for Row(S) and Null(S)

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U-1.20E-01 3.85E-02 5.39E-03 1.44E-01 -4.77E-03 3.96E-01 -2.98E-01 5.77E-01 2.03E-01 -9.68E-02 1.99E-01 -3.07E-01 -4.48E-01 1.87E-16 5.02E-17 -2.01E-17 3.01E-17 -1.00E-17 -8.03E-171.28E-01 -4.34E-02 2.66E-03 -1.66E-01 -1.49E-01 -5.71E-01 2.75E-01 -1.66E-16 -1.44E-02 1.49E-02 2.76E-01 -5.06E-01 -3.18E-01 2.63E-01 -7.39E-02 -7.28E-02 -6.70E-02 6.70E-02 -9.15E-02
-1.28E-01 3.53E-02 -2.82E-02 6.28E-02 3.88E-01 3.41E-01 4.06E-02 -5.77E-01 -1.69E-01 3.06E-02 -8.19E-02 -7.39E-02 -4.87E-01 2.63E-01 -7.39E-02 -7.28E-02 -6.70E-02 6.70E-02 -9.15E-021.25E-01 1.92E-02 8.38E-02 1.57E-01 -6.01E-01 5.17E-02 -2.65E-01 -1.94E-15 -3.77E-02 7.98E-02 -2.33E-01 2.54E-01 -6.39E-02 5.25E-01 -1.48E-01 -1.46E-01 -1.34E-01 1.34E-01 -1.83E-01
-8.64E-03 -3.13E-03 -3.36E-02 -8.17E-02 3.93E-01 -5.47E-02 3.39E-01 5.77E-01 -3.72E-01 1.27E-01 -2.81E-01 2.33E-01 -3.91E-02 2.63E-01 -7.39E-02 -7.28E-02 -6.70E-02 6.70E-02 -9.15E-02-7.26E-02 -3.42E-01 -1.64E-01 -3.92E-01 2.93E-01 -1.38E-01 -2.15E-01 1.08E-14 5.72E-01 -1.83E-01 5.97E-02 2.89E-01 7.33E-03 2.63E-01 -7.39E-02 -7.28E-02 -6.70E-02 6.70E-02 -9.15E-021.32E-01 2.21E-01 3.18E-02 4.22E-01 2.32E-01 -1.29E-01 -4.77E-02 -9.36E-17 -7.90E-03 -4.89E-01 1.49E-01 -6.78E-03 2.09E-01 1.77E-01 1.79E-01 1.87E-01 -3.72E-01 3.72E-01 3.71E-02
-8.06E-02 4.11E-02 1.89E-01 -4.61E-01 -2.50E-01 2.50E-01 2.24E-01 -3.12E-15 -1.85E-01 -1.67E-01 3.60E-01 2.93E-01 -1.36E-01 -7.07E-02 4.40E-01 -4.95E-02 -1.76E-01 1.76E-01 -8.98E-025.55E-03 -9.29E-03 -4.79E-01 2.88E-01 -3.27E-02 -2.94E-02 1.66E-01 5.20E-15 2.77E-01 5.40E-01 4.55E-02 9.44E-02 -8.66E-02 -7.07E-02 4.40E-01 -4.95E-02 -1.76E-01 1.76E-01 -8.98E-021.07E-01 -6.08E-02 5.09E-01 -8.15E-02 2.18E-01 9.31E-02 -1.82E-01 1.54E-15 6.79E-02 3.84E-01 3.68E-02 -2.59E-01 2.88E-01 -1.34E-01 -2.71E-02 -2.75E-01 -2.46E-01 2.46E-01 -3.33E-01
-6.41E-02 2.66E-01 -3.10E-01 -2.54E-01 -6.21E-02 -1.77E-01 -2.39E-01 -2.46E-15 -9.00E-02 -2.54E-01 -4.85E-01 -1.37E-01 -1.50E-01 -3.96E-01 4.67E-02 -2.02E-01 -1.79E-01 1.79E-01 -2.42E-01-9.36E-03 -1.93E-01 1.72E-01 2.22E-01 -9.67E-02 1.69E-01 5.05E-01 6.79E-15 3.35E-01 -3.61E-01 -3.30E-01 -1.54E-01 6.16E-02 1.44E-02 1.88E-01 -3.09E-01 1.29E-01 -1.29E-01 -2.18E-01-5.15E-01 2.32E-01 1.24E-02 -8.70E-02 -9.17E-02 3.92E-02 1.47E-01 3.21E-15 1.44E-01 7.73E-02 -5.19E-02 -1.16E-01 1.72E-01 1.24E-01 -1.10E-01 5.77E-01 -3.36E-03 3.36E-03 -4.57E-015.15E-01 -2.32E-01 -1.24E-02 8.70E-02 9.17E-02 -3.92E-02 -1.47E-01 -3.26E-15 -1.44E-01 -7.73E-02 5.19E-02 1.16E-01 -1.72E-01 -1.24E-01 1.52E-01 3.41E-01 1.92E-01 -1.92E-01 -5.84E-015.06E-02 -3.29E-01 -2.40E-01 -2.39E-01 -3.13E-02 2.23E-01 -1.70E-01 -3.91E-15 -2.29E-01 -4.35E-03 -1.95E-01 -4.49E-01 3.07E-01 3.26E-01 3.94E-01 1.52E-01 3.01E-03 -3.01E-03 1.52E-01
-1.07E-01 7.67E-02 4.98E-01 -1.06E-02 8.24E-02 -3.15E-01 -1.72E-01 1.89E-15 1.45E-01 1.21E-01 -3.59E-01 6.86E-02 -2.94E-01 6.31E-02 4.68E-01 2.25E-01 7.00E-02 -7.00E-02 2.43E-019.98E-02 4.58E-01 -5.96E-02 -8.61E-02 1.05E-01 8.47E-03 -7.79E-02 1.50E-15 6.20E-02 1.38E-02 1.06E-01 -1.53E-02 1.25E-01 2.13E-01 1.65E-01 -2.08E-01 7.19E-01 2.81E-01 -9.76E-02
-9.98E-02 -4.58E-01 5.96E-02 8.61E-02 -1.05E-01 -8.47E-03 7.79E-02 -1.50E-15 -6.20E-02 -1.38E-02 -1.06E-01 1.53E-02 -1.25E-01 -2.13E-01 -1.65E-01 2.08E-01 2.81E-01 7.19E-01 9.76E-025.73E-01 2.71E-01 8.66E-03 -2.85E-01 -2.73E-02 2.76E-01 2.51E-01 6.73E-15 3.23E-01 7.91E-02 -2.15E-01 -6.14E-02 -6.93E-02 -1.44E-02 -1.88E-01 3.09E-01 -1.29E-01 1.29E-01 2.18E-01
Col(S) Left Null(S)

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46
Σ4.059613 0 0 0 0 0 0 0 0 0 0 0 0 0
0 2.851793 0 0 0 0 0 0 0 0 0 0 0 00 0 2.120736 0 0 0 0 0 0 0 0 0 0 00 0 0 1.979295 0 0 0 0 0 0 0 0 0 00 0 0 0 1.878411 0 0 0 0 0 0 0 0 00 0 0 0 0 1.715997 0 0 0 0 0 0 0 00 0 0 0 0 0 1.667575 0 0 0 0 0 0 00 0 0 0 0 0 0 1.414214 0 0 0 0 0 00 0 0 0 0 0 0 0 1.377889 0 0 0 0 00 0 0 0 0 0 0 0 0 1.171902 0 0 0 00 0 0 0 0 0 0 0 0 0 1.082776 0 0 00 0 0 0 0 0 0 0 0 0 0 0.953417 0 00 0 0 0 0 0 0 0 0 0 0 0 0.603711 00 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0
r = 13, i.e., 13 linearly, independent relationships between compounds and reactions

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47
V4.56E-01 -9.62E-02 -8.89E-03 -2.13E-01 6.42E-03 -4.48E-01 3.18E-01 -4.08E-01 -1.32E-01 3.08E-02 -3.17E-02 -2.93E-02 -4.71E-01 1.62E-01
-6.30E-02 2.76E-02 -1.45E-02 1.16E-01 2.86E-01 5.31E-01 -1.41E-01 -4.08E-01 -1.12E-01 1.34E-02 -3.30E-01 4.53E-01 -2.79E-01 1.62E-014.57E-01 -7.31E-02 4.52E-02 -8.68E-03 -4.43E-01 -5.36E-02 -2.09E-01 4.08E-01 1.21E-01 -2.24E-02 -2.42E-01 5.23E-01 1.47E-02 1.62E-01
-5.08E-02 -1.28E-01 -1.33E-01 -3.19E-01 6.85E-01 -1.42E-01 2.33E-01 4.08E-01 1.73E-01 -1.16E-01 1.03E-02 2.81E-01 5.33E-02 1.62E-01-1.58E-02 -1.19E-01 -6.14E-02 -1.57E-01 -5.33E-02 -4.84E-02 -3.32E-01 -4.08E-01 6.85E-01 -2.65E-01 3.15E-01 5.92E-02 7.68E-02 1.62E-012.28E-01 7.29E-01 1.53E-01 3.01E-01 8.15E-02 4.57E-02 2.60E-01 1.82E-15 6.95E-02 -1.66E-01 2.61E-01 6.45E-02 1.26E-01 3.24E-01
-3.06E-01 9.95E-02 8.58E-02 -5.34E-01 -3.54E-01 2.66E-01 3.39E-01 1.79E-15 8.04E-02 4.07E-01 9.94E-02 7.10E-02 -6.62E-04 3.24E-012.12E-02 -1.77E-02 -3.15E-01 3.79E-01 1.16E-01 -1.63E-01 -3.52E-02 6.07E-15 3.35E-01 6.03E-01 -2.91E-01 -2.09E-01 8.13E-02 3.24E-01
-1.32E-03 8.83E-03 7.01E-01 -1.92E-01 1.77E-01 -1.12E-01 -3.12E-01 -1.18E-15 -4.64E-02 -2.96E-02 -3.40E-01 -2.99E-01 1.34E-01 3.24E-01-4.37E-01 1.82E-01 -3.79E-01 -3.10E-02 -2.32E-01 -2.72E-01 -8.84E-03 -3.37E-15 -1.40E-01 -4.80E-01 -3.80E-01 -5.18E-02 -4.05E-02 3.24E-01-1.77E-01 -5.78E-01 2.80E-01 4.71E-01 -1.16E-01 3.12E-02 3.89E-01 -1.19E-16 -1.59E-02 -1.82E-01 1.46E-01 7.91E-02 5.00E-02 3.24E-014.34E-01 -2.10E-01 -3.56E-01 -1.71E-01 2.26E-02 4.29E-01 -2.42E-02 -4.14E-15 -2.46E-01 -1.71E-01 4.92E-02 -3.64E-01 3.11E-01 3.24E-01
-2.94E-02 1.35E-02 2.54E-03 7.30E-02 -2.54E-03 2.31E-01 -1.79E-01 4.08E-01 1.47E-01 -8.26E-02 1.84E-01 -3.22E-01 -7.41E-01 1.62E-01-1.39E-01 -2.74E-02 -8.52E-02 3.17E-02 6.60E-02 -2.59E-01 -4.53E-01 -9.55E-15 -4.77E-01 2.40E-01 5.03E-01 2.26E-01 1.28E-02 3.24E-01
1 -9.76E-10 -3.19E-10 6.62E-10 -1.89E-11 3.06E-10 -6.16E-12 -2.86E-10 2.38E-10 1.28E-10 6.45E-12 -3.61E-10 7.65E-11 -2.34E-101 -5.12E-10 -6.94E-11 -3.04E-10 -3.12E-10 -2E-10 -1.22E-10 6.17E-11 4.35E-10 2.74E-10 -3.97E-11 -2.35E-11 -1.52E-10
Row(S) Null(S)

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48
Eigen-reaction
( ) ( )
( ) ( )vvxu
vVΣxU
vVUΣUxU
vVUΣSvx
TT
TT
TTT
T
:rkfor
kkk
dtd
dtd
dtd
dtd
σ=
≤
=
=
== ( )( )
∑∑>
<
>
<
∑ −⎯⎯←⎯→⎯
∑
−
−+++=
+++=
0for
0for
0for
0for
2211T
2211T
:reactionEigenpathway
pool
ki
kj
kj
ki uiki
vjkj
vjkj
uiki
nknkkk
mkmkkk
xu
vv
vv
xu
vvvvvv
xuxuxu
L
L
vv
xu

1st Mode (σ = 4.060)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 5 10 15 20
v8 2.12E-02v6 2.28E-01v12 4.34E-01
dhap -0.008642 v1 4.56E-01 2pg 0.005551lac-L -0.00936 v3 4.57E-01 pi 0.050597pyr -0.064063 nadh 0.099802g3p -0.072627 pep 0.1073193pg -0.08055 fdp 0.125139nad -0.099802 v9 -1.32E-03 g6p 0.127779h2o -0.107144 v5 -1.58E-02 13dpg 0.131546glc-D -0.119502 b1 -2.94E-02 adp 0.514654f6p -0.128144 v4 -5.08E-02 h 0.573352atp -0.514654 v2 -6.30E-02
b2 -1.39E-01v11 -1.77E-01v7 -3.06E-01v10 -4.37E-01
0
0.05
0.1
0.15
0.2
0.25
0 5 10 15
h
atpadp
u2 v2
v3 v1
v10 v12

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Mode 1

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Mode 2

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Null spaces
glc-D + atp -> g6p + adp + h v1 0.1622 1g6p <-> f6p v2 0.1622 1f6p + atp -> fdp + adp + h v3 0.1622 1fdp <-> dhap + g3p v4 0.1622 1dhap <-> g3p v5 0.1622 1g3p + pi + nad <-> 13dpg + nadh + h v6 0.3244 213dpg + adp <-> 3pg + atp v7 0.3244 23pg <-> 2pg v8 0.3244 22pg <-> pep + h2o v9 0.3244 2pep + adp + h -> pyr + atp v10 0.3244 2pyr + nadh + h <-> lac-L + nad v11 0.3244 2atp + h2o -> adp + pi + h v12 0.3244 2glc-D[e] <-> glc-D b1 0.1622 1lac-L + h <-> h[e] + lac-L[e] b2 0.3244 2
Conserved metabolite pools Steady state flux balance

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A0≤v1 ≤10
0≤v2 ≤6
0≤v3 ≤8( ) ⎟
⎟
⎠
⎞
⎜⎜
⎝
⎛−−==
3
2
1111
vvv
dtdA
dtd Svx
( )( )
A
vvv
A
vv
v
⎯⎯⎯⎯⎯ ⎯←⎯⎯⎯⎯⎯ →⎯
−−=
⋅=
−
+ 32
1
5774.05774.0
5774.0
321T1
T1
0
pathway5774.05774.05774.0
pool1:reactionEigen
vv
xu
( )( ) 0788702113057740211307887057740577405774057740
001.73211 =⎟⎟⎠
⎞⎜⎜⎝
⎛
−−−−
=.........
S

LKN/2009 Winter School in Mathematical & Computational Biology
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80601007887.02113.0
5774.0
2113.07887.05774.0
321
21
≤≤∧≤≤∧≤≤
⎟⎟⎠
⎞⎜⎜⎝
⎛−+⎟
⎟⎠
⎞⎜⎜⎝
⎛
−=
=
vvv
wwSS
SS
v
0Sv
Orthonormal basis for Null(S)
A0≤v1 ≤10
0≤v2 ≤6
0≤v3 ≤8
8060100101
011
321
21
≤≤∧≤≤∧≤≤
⎟⎟⎠
⎞⎜⎜⎝
⎛+⎟⎟⎠
⎞⎜⎜⎝
⎛=
vvv
ααSSv Convex basis for Null(S)

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100:100 211 ≤+≤≤≤ ααv
60:60 12 ≤≤≤≤ αv
80:80 23 ≤≤≤≤ αv
8060100101
011
321
21
≤≤∧≤≤∧≤≤
⎟⎟⎠
⎞⎜⎜⎝
⎛+⎟⎟⎠
⎞⎜⎜⎝
⎛=
vvv
ααSSv Convex basis for Null(S)
Since all vi≥0 and all basis elements positive: αi ≥0

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α1
0 2 4 6 8 10
α2
0
2
4
6
8
10
12
0
5
10
15
20
25
0
2
4
6
8
10
02
46
8
v 1
v 2
v3

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Linear vs convex spacesLinear space• Described by linear equations
• Vector space defined by set of linearly independent basis vectors (bi)
v = Σwibi -∞< wi <+∞
• Every point uniquely described by linear combination of bi
• Number of basis vectors equals dim(Null(S))
• Infinite number of bases can span space
Convex space• Described by linear equations
and inequalities• Convex polyhedral cone
defined by conically independent generating vectors (pi)
v = Σ αipi 0≤ αi <+∞
• Every point described by non-negative, linear combination of pi (non-unique)
• Number of generation vectors may exceed dim(Null(S))
• Unique set of generating vectors

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Extreme pathways• vss = Σ αipi 0≤ αi < αi,max• Pi’s are unique & correspond to edges in (n-r)-
dimensional cone; αi’s not unique• Correspond to pathways on a flux map • Termed extreme pathways, since they define edges of
bounded null space in its conical representation

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ExPa classificationp1 pn
v1
b1
c1
Cur
renc
yP
rimar
y
Internal fluxes
Exchange fluxes
Type IPrimary pathways
Type IIFutile cycles
Type IIIInternal cycles
≠0
≠0 ≠0
=0 =0
=0
Type I Type II Type III

v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 b1 b2 b3 b4 c1 c2 c3 c4 c5 c6 c7glc-D -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0g6p 1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 b1f6p 0 1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 glc-Dfdp 0 0 0 1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v1
dhap 0 0 0 0 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 g6pg3p 0 0 0 0 1 -1 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v2 v33pg 0 0 0 0 0 0 0 0 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 f6ppep 0 0 0 0 0 0 0 0 0 0 1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v4pyr 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 fdp
accoa 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 1 0 0 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 v5 v6acp 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 -1 1 0 0 0 0 0 0 0 0 0 0 0 dhap g3plac 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 -1 0 0 0 0 0 0 0 0 0 v7/v8 v9/v10
etoh 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 -1 0 0 0 0 0 0 0 0 3pgac 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 0 -1 0 0 0 0 0 0 0 v11/v12for 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 -1 0 0 0 0 0 0 pepatp -1 0 0 -1 0 0 0 0 1 -1 0 0 1 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 -1 0 0 0 0 0 v13adp 1 0 0 1 0 0 0 0 -1 1 0 0 -1 0 0 0 0 0 0 0 -1 1 0 0 0 0 0 0 -1 0 0 0 0 pyr lacpi 0 0 0 0 0 0 0 0 -1 1 0 0 0 0 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 0 0 0 v14 v17/v18 b2
nadh 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 0 -1 1 -2 2 0 0 0 0 0 0 0 0 0 0 -1 0 0 accoa etohnad 0 0 0 0 0 0 0 0 -1 1 0 0 0 0 0 0 1 -1 2 -2 0 0 0 0 0 0 0 0 0 0 0 -1 0 v15/16 v19/v20 b3coa 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 1 -1 0 0 1 -1 0 0 0 0 0 0 0 0 0 0 0 0 -1 acp ac
v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 b1 b2 b3 b4 c1 c2 c3 c4 c5 c6 c7 v21/v22 b4
v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 b1 b2 b3 b4 c1 c2 c3 c4 c5 c6 c7Type 3 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0glc-lac 1 1 0 1 1 0 1 0 2 0 2 0 2 0 0 0 2 0 0 0 0 0 1 2 0 0 0 2 -2 -2 0 0 0Type 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0lac-etoh 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 1 0 0 0 0 -1 1 0 1 0 0 0 -1 1 0glc-etoh 1 1 0 1 1 0 1 0 2 0 2 0 2 2 0 0 0 0 2 0 0 0 1 0 2 0 2 2 -2 -2 -2 2 0Type 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0ac-etoh 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 1 0 0 1 -1 0 -1 1 1 -2 2 0etoh-ac 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 1 0 0 0 -1 1 0 1 -1 -1 2 -2 0lac-ac 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1 0 0 1 0 0 -1 0 1 1 1 -1 -1 1 -1 0glc-ac 1 1 0 1 1 0 1 0 2 0 2 0 2 2 2 0 0 0 0 0 2 0 1 0 0 2 2 4 -4 -4 2 -2 0

v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 b1 b2 b3 b4 c1 c2 c3 c4 c5 c6 c7glc-D -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 b1g6p 1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 glc-Df6p 0 1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v1fdp 0 0 0 1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 g6p
dhap 0 0 0 0 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v2 v3g3p 0 0 0 0 1 -1 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 f6p3pg 0 0 0 0 0 0 0 0 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v4pep 0 0 0 0 0 0 0 0 0 0 1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 fdppyr 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v5 v6
accoa 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 1 0 0 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 dhap g3pacp 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 -1 1 0 0 0 0 0 0 0 0 0 0 0 v7/v8 v9/v10lac 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 -1 0 0 0 0 0 0 0 0 0 3pg
etoh 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 -1 0 0 0 0 0 0 0 0 v11/v12ac 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 0 0 0 0 1 -1 0 0 0 -1 0 0 0 0 0 0 0 pepfor 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 -1 0 0 0 0 0 0 v13atp -1 0 0 -1 0 0 0 0 1 -1 0 0 1 0 0 -2 0 0 0 0 1 -1 0 0 0 0 0 -1 0 0 0 0 0 pyr lacadp 1 0 0 1 0 0 0 0 -1 1 0 0 -1 0 0 2 0 0 0 0 -1 1 0 0 0 0 0 0 -1 0 0 0 0 v14 v17/v18 b2pi 0 0 0 0 0 0 0 0 -1 1 0 0 0 0 -1 2 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 0 0 0 accoa etoh
nadh 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 0 -1 1 -2 2 0 0 0 0 0 0 0 0 0 0 -1 0 0 v15 v19/v20 b3nad 0 0 0 0 0 0 0 0 -1 1 0 0 0 0 0 0 1 -1 2 -2 0 0 0 0 0 0 0 0 0 0 0 -1 0 acp accoa 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 1 -1 0 0 1 -1 0 0 0 0 0 0 0 0 0 0 0 0 -1 v21/v22 b4
v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 b1 b2 b3 b4 c1 c2 c3 c4 c5 c6 c7
v16
v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 b1 b2 b3 b4 c1 c2 c3 c4 c5 c6 c7Type 3 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Type 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0glc-lac 1 1 0 1 1 0 1 0 2 0 2 0 2 0 0 0 2 0 0 0 0 0 1 2 0 0 0 2 -2 -2 0 0 0ac-etoh 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 1 -1 0 -2 2 2 -2 2 0Type 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0lac-etoh 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 1 0 0 0 0 -1 1 0 1 0 0 0 -1 1 0glc-etoh 1 1 0 1 1 0 1 0 2 0 2 0 2 2 0 0 0 0 2 0 0 0 1 0 2 0 2 2 -2 -2 -2 2 0Type 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0
Futile cycle 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 0 0 -1 1 1 0 0 0etoh-ac 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 1 0 0 0 -1 1 0 1 -1 -1 2 -2 0lac-ac 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1 0 0 1 0 0 -1 0 1 1 1 -1 -1 1 -1 0glc-ac 1 1 0 1 1 0 1 0 2 0 2 0 2 2 2 0 0 0 0 0 2 0 1 0 0 2 2 4 -4 -4 2 -2 0
glc-etoh/ac 2 2 0 2 2 0 2 0 4 0 4 0 4 4 2 0 0 0 2 0 2 0 2 0 2 2 4 6 -6 -6 0 0 0

v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 v23 b1 b2 b3 b4 b5glc-D -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 b1g6p 1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 glc-Df6p 0 1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v1fdp 0 0 0 1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 g6p
dhap 0 0 0 0 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v2 v3g3p 0 0 0 0 1 -1 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 f6p3pg 0 0 0 0 0 0 0 0 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v4pep 0 0 0 0 0 0 0 0 0 0 1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 fdppyr 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 -1 1 0 0 0 0 0 0 0 0 0 0 v5 v6
accoa 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 1 0 0 -1 1 0 0 0 0 0 0 0 0 dhap g3pacp 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 -1 1 0 0 0 0 0 0 v7/v8 v9/v10lac 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 0 -1 0 0 0 3pg
etoh 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 -1 0 0 v11/v12ac 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 0 0 0 0 1 -1 0 0 0 0 -1 0 pepfor 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 v13atp -1 0 0 -1 0 0 0 0 1 -1 0 0 1 0 0 -2 0 0 0 0 1 -1 -1 0 0 0 0 0 pyr lacadp 1 0 0 1 0 0 0 0 -1 1 0 0 -1 0 0 2 0 0 0 0 -1 1 1 0 0 0 0 0 v14 v17/v18 b2pi 0 0 0 0 0 0 0 0 -1 1 0 0 0 0 -1 2 0 0 0 0 0 0 1 0 0 0 0 0 accoa etoh
nadh 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 0 -1 1 -2 2 0 0 0 0 0 0 0 0 v15 v19/v20 b3nad 0 0 0 0 0 0 0 0 -1 1 0 0 0 0 0 0 1 -1 2 -2 0 0 0 0 0 0 0 0 acp accoa 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 1 -1 0 0 1 -1 0 0 0 0 0 0 0 0 v21/v22 b4
v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 v23 b1 b2 b3 b4 b5
v16
t3 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0t3 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0t3 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0t3 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0t3 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0t3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0t3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0t3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0
glc-lac 1 1 0 1 1 0 1 0 2 0 2 0 2 0 0 0 2 0 0 0 0 0 2 1 2 0 0 0glc-lac 1 1 0 1 1 0 1 0 2 0 2 0 2 0 2 2 2 0 0 0 2 0 0 1 2 0 0 0
lac-etoh/ac 0 0 0 0 0 0 0 0 0 0 0 0 0 2 1 0 0 2 1 0 1 0 1 0 -2 1 1 2lac-etoh/ac 0 0 0 0 0 0 0 0 0 0 0 0 0 2 2 1 0 2 1 0 2 0 0 0 -2 1 1 2glc-etoh/ac 1 1 0 1 1 0 1 0 2 0 2 0 2 2 1 0 0 0 1 0 1 0 3 1 0 1 1 2glc-etoh/ac 1 1 0 1 1 0 1 0 2 0 2 0 2 2 4 3 0 0 1 0 4 0 0 1 0 1 1 2
v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 v23 b1 b2 b3 b4 b5

v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 v23 b1 b2 b3 b4 b5glc-D -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0g6p 1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 b1f6p 0 1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 glc-Dfdp 0 0 0 1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v1
dhap 0 0 0 0 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 g6pg3p 0 0 0 0 1 -1 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v2 v33pg 0 0 0 0 0 0 0 0 1 -1 -1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 f6ppep 0 0 0 0 0 0 0 0 0 0 1 -1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v4pyr 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 -1 1 0 0 0 0 0 0 0 0 0 0 fdp
accoa 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 1 0 0 -1 1 0 0 0 0 0 0 0 0 v5 v6acp 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 -1 1 0 0 0 0 0 0 dhap g3plac 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 0 -1 0 0 0 v7/v8 v9/v10
etoh 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 -1 0 0 3pgac 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 0 0 0 0 1 -1 0 0 0 0 -1 0 v11/v12for 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 pepatp -1 0 0 -1 0 0 0 0 1 -1 0 0 1 0 0 -2 0 0 0 0 1 -1 -1 0 -1 0 0 0 v13adp 1 0 0 1 0 0 0 0 -1 1 0 0 -1 0 0 2 0 0 0 0 -1 1 1 0 1 0 0 0 pyr lacpi 0 0 0 0 0 0 0 0 -1 1 0 0 0 0 -1 2 0 0 0 0 0 0 1 0 1 0 0 0 v14 v17/v18 b2
nadh 0 0 0 0 0 0 0 0 1 -1 0 0 0 0 0 0 -1 1 -2 2 0 0 0 0 0 0 0 0 accoa etohnad 0 0 0 0 0 0 0 0 -1 1 0 0 0 0 0 0 1 -1 2 -2 0 0 0 0 0 0 0 0 v15 v19/v20 b3coa 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 1 -1 0 0 1 -1 0 0 0 0 0 0 0 0 acp ac
v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 v23 b1 b2 b3 b4 b5 v21/v22 b4
v16
v1 v2 v3 v4 v5 v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 v23 b1 b2 b3 b4 b51 1 0 1 1 0 1 0 2 0 2 0 2 0 0 0 2 0 0 0 0 0 0 1 2 0 0 01 1 0 1 1 0 1 0 2 0 2 0 2 2 1 0 0 0 1 0 1 0 3 1 0 1 1 21 1 0 1 1 0 1 0 2 0 2 0 2 2 4 3 0 0 1 0 4 0 0 1 0 1 1 2

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v ∈ ℜ(n) v ∈ subspace of ℜ(n)
Sv = 0
StoichiometryLinear algebra
Eigenreactions
v = Σαipi , αi ≥ 0convex cone
ExPa
Reaction directionConvex analysis
v ≥ 0

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Pathway matrix, P, and Binary P
Binary P
( ) ( )
⎭⎬⎫
⎩⎨⎧
≠===
==
0 if1ˆ0 if0ˆ
:ˆ
|||
ijij
ijij
pppp
P
pppP 321 K
PPP)) T
LM = Pathway length matrixDiagonal elements = # reactions in each ExPaOff-diagonal elements = # shared reactions between two ExPa
TPM PPR ˆˆ= Reaction participation matrix
Diagonal elements = # ExPa in which a given reaction is found Off-diagonal elements = # ExPa that contains given pair of reactions

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JAK-STAT signaling network• Input
– 15 receptors with ligands• Output
– 7 STAT homo- and heterodimers• 297 reactions
– 216 internal– 81 irreversible exchange
• 147 extreme pathways

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Reaction participation
168 reactions participate in only one extreme pathwayVery specific function, i.e., ideal drug targets

Cross-talk• Cross-talk
– 147 ExPAs– 10,731 pairwise
comparisons
• Observations– All pathways have single
output– 99.8% disjoint output– 0.2% identical output– 63.9% deterministic– 14.8% classical cross talk

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Correlated reaction sets

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v ∈ ℜ(n) v ∈ subspace of ℜ(n)
Sv = 0
StoichiometryLinear algebra
Eigenreactions
v = Σαipi , αi ≥ 0convex cone
ExPa
Reaction directionConvex analysis
v ≥ 0

COBRA = Constraint-based reconstruction and analysis of
metabolic and regulatory networks

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v ∈ ℜ(n) v ∈ subspace of ℜ(n)
Sv = 0
StoichiometryLinear algebra
Eigenreactions
v = Σαipi , αi ≥ 0convex cone
ExPa
Reaction directionConvex analysis
v ≥ 0

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Link to real world• Defines feasible solution space in terms of balanced
pathways• Thermodynamic, regulatory, kinetic constraints
– Delete unfeasible ExPas to see true solution space• Gene KO and upregulation
– Removes all ExPas that use particular gene– Identify KO candidates among genes not required in desired
ExPas– Identify upregulation candidates among genes with high
coefficients or that are unique in desired ExPas• Max yields
– Yields calculated for individual ExPa(s)– Trade-off between biomass vs product

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v ∈ ℜ(n) v ∈ subspace of ℜ(n)
Sv = 0
StoichiometryLinear algebra
Eigenreactions
v = Σαipi , αi ≥ 0convex cone
ExPa
Reaction directionConvex analysis
v ≥ 0
Union of convex subsets
RegulationThermoKinetics

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Link to real world• Defines feasible solution space in terms of balanced
pathways• Thermodynamic, regulatory, kinetic constraints
– Delete unfeasible ExPas to see true solution space• Gene KO and upregulation
– Removes all ExPas that use particular gene– Identify KO candidates among genes not required in desired
ExPas– Identify upregulation candidates among genes with high
coefficients or that are unique in desired ExPas• Max yields
– Yields calculated for individual ExPa(s)– Trade-off between biomass vs product

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In silico E. coli model
Network:71 reactions- 21 reversible55 internal metabolites13 external metabolites
Captures:- Substrate uptake- Glycolysis- PPP, EDP, TCA-Cycle- Anaplerosis- Respiration- Fermentation- Biomass formation- 4 different pathways
for product formation

LKN/2009 Winter School in Mathematical & Computational Biology
773HP
4 natural pathways for 3HP production (KEGG)

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Left (1) Right (2) Center(3) Center-right (4)
3-HP Yield (aerobic)
95.8 % 96.6 % 84.2 % 100 % **
3-HP Yield (anaerobic)
100 % 100 % *(50%)
85.7 % 100 % **
Yields are given in C‐mol / C‐mol [%]
In general the yields are higher under anaerobic conditions
The second pathway is strongly dependent on a reversible acetate kinase.
The third pathway underperforms the other in both scenarios.
Two unknown enzymes in the fourth pathway
Effect on product formation (anaerobic, aerobic)

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3HP
#product synthesis ‐ left pathwayR54 : OAA + GLU = ASP + 2‐OXOR55 : ASP = bALA + CO2R56 : bALA + 2‐OXO = 3‐OXOPRO + GLUR57 : 3‐OXOPRO + NADH = 3‐HPA + NAD
In silico analysis of β-alanine pathway for the production of 3-HP in E. coli

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Carbon yield for 3-HP
Car
bon
yiel
d fo
r bio
mas
s 16881 elementary modes2292 make the desired product
Mode #11048Max P with X>0
AnaerobicDoes not form acetate
Does not require PEP-carboxylase and GPIHighly dependent on malic enzyme (NADPH)
Elementary mode analysis

LKN/2009 Winter School in Mathematical & Computational Biology
81Carbon yield for 3-HP
Car
bon
yiel
d fo
r bio
mas
s
464 elementary modes126 make the desired product
Knock-out of GPI, PEP-C and Acetate kinaseAnaerobic conditions

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v ∈ ℜ(n) v ∈ subspace of ℜ(n)
Sv = 0
StoichiometryLinear algebra
Eigenreactions
v = Σαipi , αi ≥ 0convex cone
ExPa
Reaction directionConvex analysis
v ≥ 0
v = Σαipi , αi ≥ 0Bounded convex cone0 ≤ αi ≤ αi,max
Capacity constraintsv ≤ vmax
Union of convex subsets
RegulationThermoKinetics

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Linear programming
nivvv
vwZ
iii
ii
,,1,and subject tomaximize
max,min, K=≤≤=
=⋅= ∑0Sv
vw Objectives• Linear
– Max growth (μ)– Max product (π)– Min substrate (σ)– Max w1μ+w2π
• Nonlinear– Min ||v||2 (QP)

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LP solutions• Shadow price (dual)
– Increase in objective function for a unit increase in a constraint
• Reduced cost– Increase in objective
function for unit increase in flux
Unique
Degenerate
Unbounded

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ExPa vs LP• ExPa
– Define all feasible points – Define all extreme points in unbounded problem
• Degenerate solutions are linear combinations of ExPas with identical objective function
– Does not define all points in bounded problem• Length constrained by capacities
– Computationally challenging• LP
– Computationally inexpensive even for large problems– Give one extreme solution point, reconstructing all more difficult– Many approaches developed

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Mixed integer programming
(binary)integer
,,1,0,,1,
and
subject to
maximize
max,min,
i
ji
iii
y
mjnynivvv
Z
K
K
=≤≤
=≤≤≥=≤
⎥⎦⎤
⎢⎣⎡
⎥⎦⎤
⎢⎣⎡⋅=
byvA
yvw

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PhPP

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Phenotypic phase plane
Ibarra et al, Nature 420, 186 - 189 (2002)

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AraGEMGene-reaction-association entries 5253ORFs (unique) 1419Metabolites 1748Unique reactions 1567
Cytosolic reactions 1265Mitochondrial reactions 60Plastidic reactions 159Peroxisomal reactions 98
Modified reactions 36Biomass drains and transporters 148
Biomass drains 47Transporters (Intercellular) 18Transporters (Inter-organelle) 83
Gaps (unique reactions ID) filled by manual curation 75Singleton metabolites 446

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AssumptionsInputs, outputs and constraints Case 1 Case 2Photons uptake (free flux) + +Glutamine transporter (mitochondria) - -Glutamate transporter(mitochondria) - -Glutamine transporter (plastid) - -Glutamate transporter (plastid) + +RuBisCO; EC 4.1.1.39 (carboxylation:oxygenation; 3:1)
- +
Fd-GOGAT ; EC 1.4.7.1 (plastid) + +NADH-GOGAT; EC 1.4.1.14 (plastid) - -Optimization: minimize uptake of Photons PhotonsBiomass rate (estimated and fixed) Leaf Leaf

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RuBisCO 3:1 C:O: ~40% increase in photon requirements (litt 30-50%)