Page 200 - Color Atlas of Biochemistry

Nucleotide Metabolism 191

A. Nucleotide synthesis: overview

1. Purine Precursors 2. Pyrimidine Precursors
1. nucleotides 2. nucleotides
De novo synthesis De novo synthesis
3
AMP IMP GMP UMP dUMP dTMP
4 4 4 4
1 1 1 1
dADP ADP GDP dGDP dCDP CDP UDP dUDP dTDP

5 5 5 5 5 5 5
2
dATP ATP GTP dGTP dCTP CTP UTP dTTP

DNA RNA RNA DNA DNA RNA RNA DNA

Ribonucleoside 2 CTP synthase 6.3.4.2 4 Nucleoside phosphate kinase 2.7.4.4
1 diphosphate
reductase 1.17.4.1 3 Thymidylate synthase 2.1.1.45 5 Nucleoside diphosphate kinase 2.7.4.6

B. Ribonucleotide reduction

NADPH N A N A NADP NTP NTP
+H P
a a
P
R1 R1
6 ATP ATP
dATP dATP
b b
S SH S S S S Substrate
Thio- S SH Thio- (NDP)
redoxin redoxin O O
(oxidized) (reduced) R2 R2
Tyrosine
radical

2. Ribonucleotide reductase
1
HS SH S S R CH 2 Base R CH 2 Base
O O
H H 1 H
H H H H
H O OH OH OH OH
2
NDP Radical
P P O Base P P O Base
O O 2
H H H H O OH H

NDP HO OH dNDP
HO
H O
H
2
Nucleoside Deoxyribonucleoside
diphosphate diphosphate R CH 2 Base R CH 2 Base
O O
H H H
H H 3 H H
1 Ribonucleoside diphosphate reductase 1.17.4.1
OH H OH
6 Thioredoxin reductase [FAD] 1.6.4.5 2e , H
dNDP
1. Overview 3. Reaction mechanism

Koolman, Color Atlas of Biochemistry, 2nd edition © 2005 Thieme
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