Nucleoside phosphorylase, coupling reactions

Mincer, J.S., Nunez, S. and Schwartz, S.D. (2004). Coupling protein dynamics to reaction center electron density in enzymes an electronic protein promoting vibration in human purine nucleoside phosphorylase. J. Theor. Comp. Chem. 3, 501-509... 

For example, intact Ehrlich ascites tumor cells, or extracts therefrom, transfer the ribosyl group of uridine to hypoxanthine and thereby catalyze the net synthesis of inosine this reaction depends upon the coupled actions of uridine phosphorylase and purine nucleoside phosphorylase (89). Similar ribosyl transfers have been demonstrated with bacterial cells and extracts. Krenitsky has studied the kinetics of exchange between uracil-2- C and nonisotopic uridine catalyzed by highly purified uridine phosphorylase (30) ... 

Purine-pyrimidine deoxyribosyl transfer reactions result when reactions (1) and (2) are catalyzed by the joint actions of purine nucleoside phosphorylase and thymidine phosphorylase, that is, when the activities of these enzymes are coupled. For example, the following reaction is catalyzed by extracts of human leukocytes (18) ... 

Much of the motivation for the study of XO electrochemistry is the development of amperometric biosensors. Commercially available bovine XO is invariably the enzyme of choice used in these applications. High levels of hypoxanthine are linked with asphyxia in newborns, SIDS and hypoxia in general. Coupled with other enzymes, such as purine nucleoside phos-phorylase, XO can be used to determine phosphate coneentrations in clinical, food and waste samples. Purine nueleoside phosphorylase catalyzes the phosphorylation of inosine liberating hypoxanthine and ribose-l-phosphate (Scheme 5.5). In the presence of XO, hypoxanthine is oxidized to xanthine and produces one equivalent of H2O2. Thus due to the stoichiometry of the reaction one equivalent of H2O2 is produced for every phosphate anion present. ... 

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