Purine nucleoside phosphorylase assays

The dialkoxyphosphinydifluoromethyllithium reagent has also been used in the preparation of bioactive compounds such as 2-amino-7,7-difluoro-7-phos-phonoheptanoic acid for evaluation in the -methyl-D-aspartic acid binding assay [265], 9-(5,5-difluoro-5-phosphonopentyl)quanine as a multisubstrate analog inhibitor of purine nucleoside phosphorylase [266], fluorinated phosphoserine analog [267, 268] (Scheme 91) and nucleoside 5 -deoxy-5 -di-fluoromethylphosphonates [267,269] (Scheme 92). 

The activity of hypoxanthine-guanine phosphoribosyltransferase, adenine phos-phoribosyltransferase, adenosine deaminase, and purine nucleoside phosphorylase can be determined in dried blood spots using an HPLC-linked assay [3]. 

Melki, R., Fievez, S., and Carlier, M.-F. (1996). Continuous monitoring of Pi release following nucleotide hydrolysis in actin or tubulin assembly using 2-amino-6-mer-capto-7-methylpurine ribonucleoside and purine-nucleoside phosphorylase as an enzyme-linked assay. Biochemistry 35, 12038-12045. 

The most recent application of RPLC to the analysis of enzymes has been reported by Halfpenny and Brown (HI). An assay for purine nucleoside phosphorylase, a key mediator in the purine salvage pathway, has been developed and optimal conditions for the analysis determined. Figure 20 illustrates the simultaneous separation of the substrate, inosine, and products, uric acid and hypoxanthine. In another analysis. Halfpenny and Brown (H2) developed an assay for hypoxanthine-guanine phos-phoribosyltransferase. Deficiency of this enzyme has been associated with Lesch-Nyhan syndrome as well as primary gout. The activity of the enzyme is determined by measurement of the decrease of the substrate, hypoxanthine, and increase in the product, inosine-5 -monophosphoric acid. A major advantage of using HPLC for enzyme assays is that the simultaneous measurement of both substrate and product reduces the error due to interference from competing enzymes. 

In a commercially available assay, serum NTP catalyzes the hydrolysis of IMP to yield inosine, which is then converted to hypoxanthine by purine-nucleoside phosphorylase (EC 2.4.2.1). Hypoxanthine is oxidized to urate with xanthine oxidase (EC 1.2.3.2). Two moles of hydrogen peroxide are produced for each mole of hypoxanthine liberated and converted to uric acid. The formation rate of hydrogen peroxide is monitored by a spectrophotometer at 510nm by the oxidation of a chromogenic system. The effect of ALPs on IMP is inhibited by p-glycerophosphate. This material is substrate for ALP but not for NTP, and by forming substrate complexes with the former enzyme, it reduces the proportion of the total ALP activity that is directed to the hydrolysis of the NTP substrate, IMP. ... 

Purine nucleoside phosphorylase was assayed in erythrocyte lysates with 450 M [8- c] inosine. ... 

Indirect Assay for Purine Nucleoside Phosphorylase-and Purine Deoxynucleoside Phosphorylase Activity... 

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