Nucleoside phosphorylase, coupling

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... 

Figure 9. Coupling of phosphopentomutase with nucleoside phosphorylase.

Scheme 5.5 Phosphate sensing based on coupled purine nucleoside phosphorylase/XO activity.

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) ... 

Coupling of purine nucleoside phosphorylase and thymidine phosphorylase in proliferating E. coli cells is demonstrated in the data of Fig. 

The simultaneous determination of sulfite and phosphate in wine was proposed by Yao et al. (1994), where a FI A system was coupled with amperometric detection. In this approach two different reactors with immobilized sulfite oxidase and co-immobilized purine nucleoside phosphorylase-xanthine oxidase were incorporated in a parallel configuration. The enzymatically generated hydrogen peroxide was selectively detected on a poly(l,2-diaminobenzene)-coated platinum electrode. Because of the different residence times at each channel, two different peaks could be obtained, the first corresponding to sulfite and the second to phosphate. Using this system, the analytes could be simultaneously analyzed with a linear range of 1 x 10 -2 x 10 M (sulfite) and 2 x 10 -5 x 10 M (phosphate) and a sample throughput of 30 Mb... 

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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