Chicken liver purine nucleoside phosphorylase activity dependency of the redox state of sulfhydryl groups

Abstract

1. 1. Double reciprocal plots (1/v vs 1/S) for nucleoside substrates of chicken liver purine nucleoside phosphorylase were non linear at high inosine or deoxyinosine concentrations (>0.1 mM). The appearance of downward curvatures may be correlated with the oxidation of sulfhydryl groups of the enzyme. 2. 2. 5,5′-Dithiobis-(2-nitrobenzoic acid) reacts with four sulfhydryl groups in the native enzyme, but upon denaturation with sodium dodecilsulfate six sulfhydryl groups react with this reagent. 3. 3. Inosine, ribose-1-phosphate, hypoxanthine and orthophosphate partially protect sulfhydryl groups from the reaction with Ellman's reagent. 4. 4. Inhibition of purine nucleoside phosphorylase by p-chloromercuribenzoate and 5,5′-dithiobis-(2-nitrobenzoic acid) follows a second order reaction kinetics.