Irreversible Inhibition of Hypoxanthine Phosphoribosyltransferase Further Studies on the Specificity of Periodate-Oxidized GMP

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Abstract
Inactivation of rat brain hypoxanthine phosphoribosyltransferase caused by periodate-oxidized GMP was irreversible, even under the conditions of polyacrylamide gel electrophoresis and during affinity chromatography on GMP-Sepharose. Partial binding of the inhibitor to the enzyme protein could be demonstrated on dodecyl-sulfate gel electrophoresis: The substrate, phosphoribosyl diphosphate in the presence of Mg2+, and the product GMP protected the enzyme against inactivation. Periodate-oxidized GMP, AMP and oxidized purine nucleosides did not influence ribosephosphate pyrophosphokinase, 5''-nucleotidase, purine-nucleoside phosphorylase and guanylate kinase. A variety of other purine nucleosides and nucleotides, tested in their periodate-oxidized form, did not lead to a compound comparable or superior to oxidized GMP in its effect on hypoxanthine phosphoribosyltransferase. In a human erythrocyte system it was clearly demonstrated that oxidized GMP could not act across an intact cell membrane.