Lecture 2

• August 3, 2005

• Lehninger (4th Edition), Chapter 6,

ENZYME KINETICS

LNC Chapter 6

REACTANTS

SUBSTRATESPRODUCTS

kFirst order reactions: A P

kSecond order reactions: A + B P

A + A P

1st order: ln[A] = ln[Ao] - kt or [A] = [Ao] exp(-kt)

2nd order: 1/[A] = 1/[Ao] + kt

time

[A]

time

[A]

1

time

ln [A]

TRANSITION STATE THEORY

A C

B D

A C

B D

A C

B D

A catalyst serves in at least two ways:it binds and aligns the substratesit facilitates the redistribution of electrons (charges)

k1 k2

E + S ES Products k-1

CHAPTER 6

Enzymes and Enzyme Kinetics

Fig. 6-2

Fig. 6-3

Derivation of Michaelis-Mentenequation

• 1. equilibrium assumption: k-1 >> k2

• 2. steady state assumption: d[ES]/dt = 0

• Note: [E] = [E]total – [ES]

Hmmm..??

when [S] >> Km

then

v vmax and vmax = k 2 [E] T

k2 x [E]T x [S]v = ------------------------- Km + [S]

k -1 + k 2 Km =

k 1

d

Km Kd

when

k -1 >> k 2

Fig. 6-11

Fig. 6-12

1 Km 1 1 = x +vo v max [S] v max

y = ax + b

Lineweaver-Burk Plot

Double Reciprocal Plotbox. 6-1

- another definition:

v max

k2 = k cat = ------------ [E] T

TURNOVER NUMBER

molecules of substrate / molecule of enzyme / second

moles of substrate / mole of enzyme / second

Reactions with more than one substrate

(more typical)

Overall reaction:

S1 + S2 P1 + P2

Fig. 6-13

LNC 6-14 a

Lines intersect: ternary complex is formed in the reaction

LNC 6-13 b

This case is also referred to as the Ping-Pongor

double displacement mechanism

LNC 6-14 b

Lines do not intersect: no ternary complex is formed

Enzyme Inhibitors

Fig. 6-15a

Competitive Inhibition

= 1 + [I] / KI

box. 6-2.1

Fig. 6-15b

Uncompetitive Inhibition

’ = 1 + [I] / KI

box. 6-2.2

Fig. 6-15c

Mixed Inhibition

When = ’, then we also speak of noncompetitive inhibition

box 6-2.3

LNC 6-28

FEEDBACK INHIBITION

LNC 6-26

LNC 6-27

ASPARTATE TRANSCARBAMYLASE

LNC 6-29a

LNC 6-29b

LNC 6-29c

Part III

Bioenergetics and MetabolismChapter 13 in LNC

THE CARBON CYCLE

urea

THE NITROGEN CYCLE

Types of Organic Reactions

1) Group transferGlucose + ATP Glu-6-P + ADPH2O + ATP Pi + ADP

2) Oxidation-reduction reactionsEthanol + NAH+ acetaldehyde + NADH + H+

3) Eliminations, isomerizations, rearrangementsaldose ketose

4) reactions involving making or breaking of C-C bondsFru-1,6, bisphosphate dihydroxyacetone-phosphate

+ glyceraldehyde-3phosphate

• End of Lecture 2

• Aug. 3, 2005