3. metab purin- pirimidin.ppt
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RETNO SINTOWATI
Purin, Pirimidin, Asam nukleat
I. Pendahuluan II. Basa Purin dan Basa Pirimidin III. Nukleosida IV. Nukleotida V. Asam Nukleat
Kepentingan biomedis
kemampuan nukleotid menyerap sinar UV menjadikan sinar UV sbg unsur mutagen yg potent
senyawa analog purin & pirimidin disintesis secara kimiawi digunakan untuk terapi penyakit kanker
Sel yg akan membelah, selnya mengalami replikasi
Katabolisme purin xantin asam urat
I. PendahuluanNukleoprotein
protein majemuk terdapat dalam inti sel penyusun material inti sel tersusun atas : protein: histon / protamin
gugus non protein semua sel hidup mengandung nukleoprotein
KromatinKonstituen penting dalam sel, tersusun atas
nukleoprotein kelainan pembentukan nukleoprotein
perubahan dlm pertumbuhan /reproduksi sel
sebab kromatin pembelahan sel
Nukleosida Purin
Adenosin Guanosin adenosin deaminase purin nukleosida fosforilase
NH3 Inosin Guanin purin nukleosida
fosforilase Hipoxantin Xantin oksidase
Xantin + O2 asam urat urin Xantin oksidase
Penyelamatan Purin Untuk pembentukan nukleotida bbrp jaringan
manusia tgt pd purin /purin ribonukleosida eksogen Ada 2 jalan penyelamatan :1. Fosforibosilasi purin bebas dgn enzim yang
membutuhkan PRPP sbg donor ribosa fosfat2. Fosforilasi nukleosida purin pd gugus 5’-
hidroksi oleh enzim adenosin kinaseContoh :1. Adenin menjadi AMP dg enzim adenin
fosforibosa transferase2. Hipoxantin dan Guanin menjadi IMP dan GMP
dengan enzim hipoxantin-guanin fosforibosa transferase
Nukleosida pirimidin Sitidin Deoksisitidin deaminasi Uridin deaminasi
Deoksiuridin Deoksitimidin
fosforilse
Urasil dan Timin degradasi
-alanin + NH4+ +CO2 degradasi
As. -amino isobutirat + NH4+ +CO2
urine
Banyak tdp pd penderita tumor yang dikhemoterapi ( DNA degradasi )
II. Basa Purin Dan Basa Pirimidin
Basa PurinBasa heterosiklis , molekul planar , aromatik sebag. besar tdp. dlm sel dlm. bentuk asam
nukleatdisintesis secara de novo, dg sumber :
N1 dari as. Aspartat, C6 dr CO2 respirasi, N7 dari glisin, C8 dari N5,N10-metenilFH4,
N3 dan N9 dari nitrogen amida der. Glutamin danC2 dari N-formil -tetrahidroksi folat
Diberi nomor mulai atom N1 kearah kebalikan jarum jam
Basa Pirimidinnama lebih panjang dari purin ttp hy
mgd 6 atom yang heterosiklis, sedang purin
nama pendek mgd 9 atom heterosiklis
Sitosin (S): tdp dlm semua asam nukleat,
kecuali DNA virus ttt
Timin (T) : trtm tdp dlm as nukleatyg mgd gula deoksiribosa (DNA);
sedikit tdp dlm tRNA Urasil (U): tdp dalam RNA
Nitrogenous BasesPlanar, aromatic, and heterocyclicDerived from purine or pyrimidineNumbering of bases is “unprimed”
Nucleic Acid BasesPurines Pyrimidines
SugarsPentoses (5-C sugars)Numbering of sugars is “primed”
Sugars D-Ribose and 2’-Deoxyribose
*Lacks a 2’-OH group
NucleosidesResult from linking one of the sugars with a
purine or pyrimidine base through an N-glycosidic linkage
Purines bond to the C1’ carbon of the sugar at their N9 atoms
Pyrimidines bond to the C1’ carbon of the sugar at their N1 atoms
Nucleosides
Phosphate GroupsMono-, di- or triphosphates
Phosphates can be bonded to either C3 or C5 atoms of the sugar
NucleotidesResult from linking one or more
phosphates with a nucleoside onto the 5’ end of the molecule through esterification
III. Nukleosida dan nukleotidaNukleosida:
- tdr dari basa + d-ribosa gula ribosa terikat
pada N9 basa purin dan pada N1 basa
pirimidin (kecuali U pd C5 ikatan C-C) dan semuanya mrpk ikatan -N-glikosidik
- Nukleosida yang dimanfaatkan untuk menghambat pertumbuhan sel:
- 5-fluorourasil - 5’-iodo-2’-deoksiuridin
- 6-tioguanin - 6-merkaptopurin- 6-azauridin - arabinosil sitosin
NukleotidaMrpk unit struktural as nukleat, mrpk komponen seluler yg mudah dpt diketahui krn menyerap kuat sinar UV, der. basa
purin absorbsinya lebih kuat dari der. basa pirimidinTersusun: - basa purin/ basa pirimidin
- gula (ribosa atau 2-deoksiribosa), - asam fosfatPengikatan fosfat: RNA pd at C3’ dari gulanya DNA pd at C5’ dari gulanya
Basa Nukleosida Nukleotida Singkatan RNA DNA
Adenin Adenosin Asam adenilat A dA
Guanin Guanosin Asam guanilat G dG
Sitosin Sitidin Asam Sitidilat C dCUrasil Uridin Asam uridilat U
dUTimin Timidin Asam timidilat T
dT
Lanjutan nukleotida
- bentuk nukleotida lebih mudah larut dalam air dp nukleosida dan basa bebasnya
Fungsi nukleotida 1. Berperan dlm metabolisme energi
Contoh: ATP - bentuk energi kimia yang diperlukan untuk sel, dihasilkan dari fosforilasi oksidatif atau fosforilasi tingkt
substrat - terlibat dalam kontraksi otot - transport aktif - mempertahankan gradien/ion - membantu sbg donor fosfat untuk
sin- tesis nukleosida 5’-trifosfat substrat untuk reaksi yg dikatalisis oleh RNA dan DNA polimerase
Lanjutan fungsi nukleotida
2. Monomer unit asam nukleat: DNA dan RNA3. Mediator fisiologik: nukleosida dan nukleotida
membantu sbg kunci mediator fisiologik proses metabolik:
- adenosin penting dlm kontrol aliran darah koroner - ADP critical dlm agregasi platelet dan koagulasi darah - cAMP & cGMP: bekerja sbg second messenger - GTP: diperlukan untuk capping mRNA4. Precursor function: GTP adalah prekursor pemben- tukan kofaktor, tetrahidrobiopterin, untuk reaksi
hidroksilasi dan generasi oksida nitrat5. Komponen koenzim: NAD, NADP, FAD
Lanjutan fungsi nukleotida6. Activated intermediate
- nukleotida membantu sbg kunci activated intermediate, diperlukan untuk berbagai reaksi
- UDP-glukosa-kinase intermidiate sintesis glikogen, glikoprotein dll.
7. Allosteric effectors pd metabolisme nukleotida
Sintesis nukleotida - Di dalam sel mamalia disintesis secara de novo- Tidak semua sel mampu mensintesis nukleotid
purin Contoh; sel-sel darah merah- Pada akhir reaksi menghasilkan ITP
prekursor adenosin 5’-monofosfat (AMP) dan guanosin 5’-mono-
- Fosfat (GMP)
Lanjutan sintesis nukleotida
- IMP AMP energinya dari GTP- IMP GMP energinya dari ATP- Apabila terjadi defek dlm reaksi metabolik
menyebabkan kehilangan pengaturan sintesis nukleotida purin over produksi purin asam urat meningkat
Artritis gout Pembentukan deoksi ribonukleotida
- pada keadaan sel tidak proliferasi rendah
- pada saat replikasi sintesis DNA sintesis deoksiribonukleotida meningkat untuk mensuport sintesis DNA
IV. Asam nukleat (Polinukleotid)dibentuk dari ikatan fosfodiester yg
terikat pada C3’- dan C5’ monomer yg berdekatan
ada mol. yg berakhir 5’ dan 3’masing-masing mol. memp. struktur
primernya, contoh 5’-3’p Gp Gp Ap Tp Cp A
Ada 2 macam asam nukleat besar: DNA & RNA
Nucleotide MetabolismPURINE RIBONUCLEOTIDES: formed de novo
i.e., purines are not initially synthesized as free basesFirst purine derivative formed is Inosine Mono-
phosphate (IMP) The purine base is hypoxanthine AMP and GMP are formed from IMP
Purine NucleotidesGet broken down into Uric Acid (a purine)
Buchanan (mid 1900s) showed where purine ring components came from:
N1: Aspartate AmineC2, C8: FormateN3, N9: GlutamineC4, C5, N7: GlycineC6: Bicarbonate Ion
Formyl-THFFormyl-THF
N
NC
CC
CC
N
NH
H
H
H
H
H
Glutamine Glutamine
Aspartate
CO2
Glycine
HN
N
C
C
C
CC
N
NH
H
H
H
H
H
Purine
N
NC
CC
C
H
H
H
H
Pyrimidine
H
H
GlycineGlutamine (2)AspartateN10-Formyl-THF (2)CO2
GlutamineAspartateCO2
(C5H7N4) (C4H6N2)
Purine Nucleotide Synthesis
OH
H
H
CH2
OH OH
H HO
O2-O3P
-D-Ribose-5-Phosphate (R5P)
O
H
H
CH2
OH OH
H HO
O2-O3P
5-Phosphoribosyl--pyrophosphate (PRPP)
P
O
O
O P
O
O
O
ATP
AMP
RibosePhosphatePyrophosphokinase
H
NH2
H
CH2
OH OH
H HO
O2-O3P
-5-Phosphoribosylamine (PRA)
AmidophosphoribosylTransferase
Glutamine + H2O
Glutamate + PPi
H
NH
H
CH2
OH OH
H HO
O2-O3P
CO
H2C NH2
Glycinamide Ribotide (GAR)
GAR Synthetase
Glycine + ATP
ADP+ Pi
H2C
CNH
O
CH
HN
O
Ribose-5-Phosphate
Formylglycinamide ribotide (FGAR)
H2C
CNH
O
CH
HN
HN
Ribose-5-Phosphate
Formylglycinamidine ribotide (FGAM)
THFN10-Formyl-THF
GAR Transformylase
ATP +Glutamine +H2O
ADP +Glutamate + Pi
FGAM Synthetase
HC
CN
CH
N
H2N
Ribose-5-Phosphate
4
5
5-Aminoimidazole Ribotide (AIR)
ATP
ADP + Pi
AIR Synthetase
C
CN
CH
N
H2N
OOC
Ribose-5-Phosphate
4
5
Carboxyamidoimidazole Ribotide (CAIR)
ATP+HCO3
ADP + PiAIR Car boxylase
Aspartate+ ATP
ADP+ Pi
SAICAR Synthetase
AdenylosuccinateLyase
Fumarate
C
CN
CH
N
NH
Ribose-5-Phosphate
4
5
5-Formaminoimidazole-4-carboxamideribotide (FAICAR)
CH2N
O
CH
O
C
CN
CH
N
H2N
Ribose-5-Phosphate
4
5
5-Aminoimidazole-4-carboxamideribotide (AICAR)
CH2N
O
C
CN
CH
N
H2N
CNH
O
HC
COO
CH2
COO
Ribose-5-Phosphate
4
5
5-Aminoimidazole-4-(N-succinylocarboxamide)ribotide (SAICAR)
THF
AICAR Transformylase
N10-Formyl-
THF
Inosine Monophosphate (IMP)
HN
HCN
C
CC
N
CH
N
O
4
5
HH
CH2
OH OH
H HOO2-O3P
IMPCyclohydrolase
H2O
Ribose-P
HCN
C
CC
N
N
CH
N
NH2
Ribose-P
CN
C
CC
HN
N
CH
N
O
HO
Ribose-P
CN
C
CC
HN
N
CH
N
O
H2N
Ribose-P
HCN
C
CC
HN
N
CH
N
O GTPAspartate
GDP + Pi
Fumarate
ATPGlutamine
ADP + Pi
Glutamate
H2O + NAD+
NADH + H+
AMP
GMP
IMP is converted to AMP or GMP
IMP
XMP
Regulatory Control of Purine Nucleotide Biosynthesis
GTP is involved in AMP synthesis and ATP is involved in GMP synthesis (reciprocal control of production)
PRPP is a biosynthetically “central” molecule (why?)ADP/GDP levels – negative feedback on Ribose Phosphate
Pyrophosphokinase Amidophosphoribosyl transferase is activated by PRPP levelsAPRT activity has negative feedback at two sites
ATP, ADP, AMP bound at one site GTP,GDP AND GMP bound at the other site
Rate of AMP production increases with increasing concentrations of GTP; rate of GMP production increases with increasing concentrations of ATP
Regulatory Control of Purine BiosynthesisAt level of IMP production:
Independent controlSynergistic controlFeedforward activation by PRPP
Below level of IMP productionReciprocal control
Total amounts of purine nucleotides controlled
Relative amounts of ATP, GTP controlled
Purine Catabolism and SalvageAll purine degradation leads to uric acid (but it
might not stop there)Ingested nucleic acids are degraded by pancreatic
nucleases, and intestinal phosphodiesterases in the intestine
Group-specific nucleotidases and non-specific phosphatases degrade nucleotides into nucleosidesDirect absorption of nucleosides Further degradation
Nucleoside + H2O base + ribose (nucleosidase) Nucleoside + Pi base + r-1-phosphate (n. phosphorylase)
NOTE: MOST INGESTED NUCLEIC ACIDS ARE DEGRADED AND EXCRETED.
Intracellular Purine CatabolismNucleotides broken into nucleosides by action
of 5’-nucleotidase (hydrolysis reactions)Purine nucleoside phosphorylase (PNP)
Inosine HypoxanthineXanthosine XanthineGuanosine GuanineRibose-1-phosphate splits off
Can be isomerized to ribose-5-phosphate
Adenosine is deaminated to Inosine (ADA : Adeosine deaminase)
Intracellular Purine CatabolismXanthine is the point of convergence for
the metabolism of the purine bases
Xanthine Uric acidXanthine oxidase catalyzes two reactions
Purine ribonucleotide degradation pathway is same for purine deoxyribonucleotides
Adenosine Degradation
Xanthosine Degradation
• Ribose sugar gets recycled (Ribose-1-Phosphate R-5-P ) – can be incorporated into PRPP (efficiency)• Hypoxanthine is converted to Xanthine by Xanthine Oxidase• Guanine is converted to Xanthine by Guanine Deaminase• Xanthine gets converted to Uric Acid by Xanthine Oxidase
GMP AMP ↓ ↓ Guanosin IMP ↓ ↓ ↓ Inosin
↓ Guanin Hipoxantin
↓ ٭↓ Xantin ٭ ↓
Asam urat URIN tmp kerja xantin oxidase, dihambat oleh ٭
Alopurinol
Uric Acid ExcretionHumans – excreted into urine as insoluble crystalsBirds, terrestrial reptiles, some insects – excrete
insoluble crystals in paste form (hewan urikotelik)Excess amino N converted to uric acid
Others – further modification :
Uric Acid Allantoin Allantoic Acid Urea Ammonia
Ekskresi asam urat total man 400-600mg/24jamAspirin dosis tinggi hambat ekskresi & reabsorpsi urat.
Purine Salvage(Jalur penyelamatan purin)Adenine phosphoribosyl transferase (APRT)
Adenine + PRPP AMP + PPi
Hypoxanthine-Guanine phosphoribosyl transferase (HGPRT)
Hypoxanthine + PRPP IMP + PPi
Guanine + PRPP GMP + PPi
(NOTE: THESE ARE ALL REVERSIBLE REACTIONS)
AMP,IMP,GMP do not need to be resynthesized de novo !
Di hati : nukleotida defosforilasi nukleosida
Sering nukleosida diputus basa bebas + gula
nukleosida & basa dibawa ke jar lain refosforilasi mjd nukleotida
Basa bebas diselamatkan dg mereaksikan dg PRPP nukleotida baru
Enzim penghemat basa tsb HGPRTReaksi analog juga terjadi utk pirimidin
A CASE STUDY : GOUTA 45 YEAR OLD MAN AWOKE FROM SLEEP WITH A
PAINFUL AND SWOLLEN RIGHT GREAT TOE. ON THE PREVIOUS NIGHT HE HAD EATEN A MEAL OF FRIED LIVER AND ONIONS, AFTER WHICH HE MET WITH HIS POKER GROUP AND DRANK A NUMBER OF BEERS.
HE SAW HIS DOCTOR THAT MORNING, “GOUTY ARTHRITIS” WAS DIAGNOSED, AND SOME TESTS WERE ORDERED. HIS SERUM URIC ACID LEVEL WAS ELEVATED AT 8.0 mg/dL (NL < 7.0 mg/dL).
THE MAN RECALLED THAT HIS FATHER AND HIS GRANDFATHER, BOTH OF WHOM WERE ALCOHOLICS, OFTEN COMPLAINED OF JOINT PAIN AND SWELLING IN THEIR FEET.
A CASE STUDY : GOUTTHE DOCTOR RECOMMENDED THAT THE MAN
USE NSAIDS FOR PAIN AND SWELLING, INCREASE HIS FLUID INTAKE (BUT NOT WITH ALCOHOL) AND REST AND ELEVATE HIS FOOT. HE ALSO PRESCRIBED ALLOPURINOL.
A FEW DAYS LATER THE CONDITION HAD RESOLVED AND ALLOPURINOL HAD BEEN STOPPED. A REPEAT URIC ACID LEVEL WAS OBTAINED (7.1 mg/dL). THE DOCTOR GAVE THE MAN SOME ADVICE REGARDING LIFE STYLE CHANGES.
Impaired excretion or overproduction of uric acid
Uric acid crystals precipitate into joints (Gouty Arthritis), kidneys, ureters (stones)
Lead impairs uric acid excretion – lead poisoning from pewter drinking gobletsFall of Roman Empire?
Xanthine oxidase inhibitors inhibit production of uric acid, and treat gout
Allopurinol treatment – hypoxanthine analog that binds to Xanthine Oxidase to decrease uric acid production
ALLOPURINOL IS A XANTHINE OXIDASE INHIBITOR
A SUBSTRATE ANALOG IS CONVERTED TO AN INHIBITOR, IN THIS CASE A “SUICIDE-INHIBITOR”
Pyrimidine Ribonucleotide Synthesis Uridine Monophosphate (UMP) is
synthesized firstCTP is synthesized from UMP
Pyrimidine ring synthesis completed first; then attached to ribose-5-phosphate
N1, C4, C5, C6 : AspartateC2 : HCO3
-
N3 : Glutamine amide Nitrogen
2 ATP + HCO3- + Glutamine + H2O
CO
O PO3-2
NH2
Carbamoyl Phosphate
NH2
CNH
CH
CH2
C
COOO
HO
O
Carbamoyl Aspartate
HN
CNH
CH
CH2
C
COOO
O
Dihydroorotate
HN
CNH
C
CHC
COOO
O
Orotate
HN
CN
C
CHC
COOO
O
HH
CH2
OH OH
H HO
O2-O3P
Orotidine-5'-monophosphate(OMP)
HN
CN
CH
CHC
O
O
HH
CH2
OH OH
H HO
O2-O3P
Uridine Monophosphate(UMP)
2 ADP +Glutamate + Pi
CarbamoylPhosphateSynthetase II
AspartateTranscarbamoylase(ATCase)
Aspartate
Pi
H2O
Dihydroorotase
Quinone
ReducedQuinone
DihydroorotateDehydrogenase
PRPP PPi
Orotate PhosphoribosylTransferase
CO2
OMP Decarboxylase
Pyrimidine Synthesis
UMP UTP and CTPNucleoside monophosphate kinase
catalyzes transfer of Pi to UMP to form UDP; nucleoside diphosphate kinase catalyzes transfer of Pi from ATP to UDP to form UTP
CTP formed from UTP via CTP Synthetase driven by ATP hydrolysis
Glutamine provides amide nitrogen for C4 in animals
Regulatory Control of Pyrimidine SynthesisAnimals – regulation at carbamoyl phosphate
synthetase IIUDP and UTP inhibit enzyme; ATP and PRPP
activate itUMP and CMP competitively inhibit OMP
Decarboxylase
*Purine synthesis inhibited by ADP and GDP at ribose phosphate pyrophosphokinase step, controlling level of PRPP also regulates pyrimidines
Caused by defect in protein chain with enzyme activities of last two steps of pyrimidine synthesis
Increased excretion of orotic acid in urine
Symptoms: retarded growth; severe anemia
Only known inherited defect in this pathway (all others would be lethal to fetus)
Treat with uridine/cytidine HOW DOES URIDINE AND CYTIDINE
ADMINISTRATION WORK TO TREAT OROTIC ACIDURIA?
Degradation of PyrimidinesCMP and UMP degraded to bases similarly to
purines DephosphorylationDeaminationGlycosidic bond cleavage
Uracil reduced in liver, forming -alanine Converted to malonyl-CoA fatty acid
synthesis for energy metabolism
Deoxyribonucleotide FormationPurine/Pyrimidine degradation are the same
for ribonucleotides and deoxyribonucleotidesBiosynthetic pathways are only for
ribonucleotide production Deoxyribonucleotides are synthesized from
corresponding ribonucleotides Pd tingkat difosfat,gugus ribosa direduksi mjd
deoksiribosa o/ enz Ribonukleotida reduktase.ex. CTP defosforilasi CDP reduksi dCDP
dCTP defosforilasi dan deaminasi dUMP
Katabolisme pirimidin menghasilkan metabolit yg dpt larut dalam air, yaitu : CO2, NH3, B-alanin, B-aminoisobutirat
Produk katab purin tidak begitu mudah larut, kelarutan ditingkatkan dg alkalinisasi.
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