Metabolism of nucleotides

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Metabolism of Nucleotides
R. C. Gupta Department of Biochemistry National
Institute of Medical Sciences Jaipur, India
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Digestion
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Synthesis of nucleotides
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De novo synthesis of purine nucleotides
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Formation of ATP and GTP
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Regulation of de novo synthesis
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PRPP glutamyl amidotransferase catalyses the
first reaction unique to purine nucleotide
synthesis
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This is the main regulatory enzyme
It is allosterically inhibited by GMP
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Synthesis of purine nucleotides by salvage
pathway

• Pre-existing purine bases and nucleosides may be
  salvaged to form new nucleotides
• Conversion of purine bases into nucleotides is
  catalysed by two enzymes

Adenine phosphoribosyl transferase (APRT)
Hypoxanthine-guanine phosphoribosyl
transferase (HGPRT)
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Regulation of salvage pathway
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Catabolism of purines
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NH2
N
Adenosine
Purine nucleoside phosphorylase
N
deaminase
H2O
NH3
Pi
Ribose-1-P
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N
N

Ribose
R C G
Adenosine
Inosine
Hypoxanthine
Xanthine oxidase
Xanthine oxidase
H2O2
H2O2
O2 H2O
O2 H2O
Xanthine
Uric acid
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Guanine
R C G
Guanosine
H2O
Guanase
NH3
Xanthine oxidase
H2O2
O2 H2O
Xanthine
Uric acid
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De novo synthesis of pyrimidine nucleotides
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Second reaction
Aspartate transcarbamoylase
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Pi
Carbamoyl phosphate
Carbamoyl aspartate
Aspartate
Carbamoyl group transferred to aspartate
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Fourth reaction
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Dihydro-orotate
Orotate
Dihydro-orotate oxidized to orotate
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Thymidylate
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Regulation of de novo synthesis
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Synthesis of pyrimidine nucleotides by salvage
pathway
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Formation of deoxyribonucleotides
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Catabolism of pyrimidines
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Thank you