title: Rabbit erythrocyte purine nucleoside phosphorylase. Initial-velocity studies.
abstract: 1. Concave-downward double-reciprocal plots were obtained for rabbit erythrocyte purine nucleoside phosphorylase when the concentration of Pi was varied over a wide range at a fixed saturating concentration of either inosine or deoxyinosine. Similar behaviour was also displayed by the calf spleen enzyme. 2. The degree of curvature of double-reciprocal plots was greatly modified by the presence of SO42-, introduced into the assay mixture with the linking enzyme xanthine oxidase; competitive inhibition by SO42- was observed over a narrow range of high Pi concentrations. 3. Partial inactivation with 5,5'-dithiobis-(2-nitrobenzoic acid) resulted in a marked alteration in the kinetic properties of the enzyme when Pi was the variable substrate. 4. Initial-velocity data are expressed in the form of Hill plots, and the significance of such plots is discussed.
mesh_terms: D000818:Animals; D002417:Cattle; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004912:Erythrocytes / Q000201:enzymology*; D007700:Kinetics; D010430:Pentosyltransferases / Q000097:blood*; D010710:Phosphates / Q000378:metabolism; D011683:Purine-Nucleoside Phosphorylase / Q000037:antagonists & inhibitors / Q000097:blood*; D011817:Rabbits; D013154:Spleen / Q000201:enzymology; D013431:Sulfates / Q000494:pharmacology
chemical_list: D010710:Phosphates; D013431:Sulfates; D004228:Dithionitrobenzoic Acid; D010430:Pentosyltransferases; D011683:Purine-Nucleoside Phosphorylase