The salvaged bases and nucleosides can then be converted back into nucleotides.
The salvage pathway requires distinct substrates:
Uridine phosphorylase adds ribose-1-phospate to the free base uracil, forming uridine monophosphate. Uridine kinase then phosphorylates this nucleoside into its diphosphate and triphosphate forms. Deoxythymidine phosphorylase adds deoxyribose-1-phosphate to thymine, forming deoxythymidine monophosphate. Thymidine kinase can then phosphorylate this compound to deoxythymidine diphosphate and triphosphate.
Phosphoribosyltransferases add activated ribose-5-phosphate (called phosphoribosyl pyrophosphate or PRPP) to bases, creating nucleotide monophosphates. There are two types of phosphoribosyltransferases: adenosine phosphoribosyltransferase (APRT) and hypoxanthine-guanine phosphoribosyltransferase (HGPRT). Lesch-Nyhan syndrome is associated with a deficiency of HGPRT.
Nucleoside Enzyme Nucleotide hypoxanthine hypoxanthine/guanine phosphoribosyl transferase (HGPRT) IMP guanine hypoxanthine/guanine phosphoribosyl transferase (HGPRT) GMP adenine adenine phosphoribosyltransferase (APRT) AMP Metabolism (Catabolism, Anabolism) General Cellular respirationAerobic Respiration Specific pathsHumanNonhumanOtherNucleotide metabolismOther Purine metabolismAnabolism
R5P->IMP: Ribose-phosphate diphosphokinase · Amidophosphoribosyltransferase · Phosphoribosylglycinamide formyltransferase · AIR synthetase (FGAM cyclase) · Phosphoribosylaminoimidazole carboxylase · Phosphoribosylaminoimidazolesuccinocarboxamide synthase · IMP synthaseGMP: IMP dehydrogenase · GMP synthase · reverse (GMP reductase)Nucleotide salvageCatabolism
Pyrimidine metabolismAnabolismCatabolism Deoxyribonucleotides
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