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Biosynthesis and Degradation of Nucleotides:- Nucleoside Monophosphates Are Converted to Nucleoside Triphosphates

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  p868-869

2026-07-08

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Biosynthesis and Degradation of Nucleotides:- Nucleoside Monophosphates Are Converted to Nucleoside Triphosphates

Nucleotides to be used in biosynthesis are generally con verted to nucleoside triphosphates. The conversion pathways are common to all cells. Phosphorylation of AMP to ADP is promoted by adenylate kinase, in the reaction

ATP+AMP ⇌2ADP

The ADP so formed is phosphorylated to ATP by the glycolytic enzymes or through oxidative phosphorylation. ATP also brings about the formation of other nucleoside diphosphates by the action of a class of en zymes called nucleoside monophosphate kinases. These enzymes, which are generally specific for a particular base but nonspecific for the sugar (ribose or deoxyribose), catalyze the reaction

ATP+NMP⇌ ADP+NDP

The efficient cellular systems for rephosphorylating ADP to ATP tend to pull this reaction in the direction of products. Nucleoside diphosphates are converted to triphosphates by the action of a ubiquitous enzyme, nucleoside diphosphate kinase, which catalyzes the reaction

NTP_D+NDP_A⇌NDP_D+NTP_A

This enzyme is notable in that it is not specific for the base (purines or pyrimidines) or the sugar (ribose or deoxyribose). This nonspecificity applies to both phosphate acceptor (A) and donor (D), although the donor (NTPD) is almost invariably ATP, because it is present in higher concentration than other nucleoside triphosphates under aerobic conditions.