METABOLISM OF MAMMALIAN ERYTHROCYTES: V. ROLE OF CATALASE IN THE OXIDATION OF RIBOSE-5-PHOSPHATE BY THE ERYTHROCYTE

Abstract

Ribose-5-phosphate has been found to be rapidly oxidized by the stroma-free hemolyzate of human, rat, and rabbit erythrocytes in the presence of ferricyanide under anaerobic conditions, or in the presence of methylene blue under aerobic conditions. Compounds resembling R-5-P, such as ribose, arabinose, xylose, glucose, glucose-6-phosphate, fructose-6-phosphate, and hexose diphosphate are not oxidized under these conditions. The oxidation does not involve DPN or TPN and it is completely inhibited by cyanide. The Ks is about 2 × 10−2 M. Under anaerobic conditions, in the presence of ferricyanide, the enzyme responsible for the oxidation is catalase. Purified catalase from beef liver or from rabbit erythrocytes yields the same results as the SFH from human, rat, or rabbit erythrocytes with respect to specificity, cyanide sensitivity, and the Ks value. Under aerobic conditions, catalase is responsible also for the oxidation of R-5-P, but the mechanism involves the peroxidase action of catalase. Catalase catalyzes the oxidation of R-5-P by hydrogen peroxide in the presence of a system which slowly generates hydrogen peroxide, such as the glucose–glucose oxidase or the hemoglobin – methylene blue systems.