The reduction of cytochrome c by hypoxanthine and xanthine oxidase

Abstract

The ability of oxidized cytochrome c to act as a H acceptor in the hypoxanthine-xanthine oxidase system was confirmed. In all the prepns. studied the anaerobic rate of reduction of cytochrome c was greater than that under-aerobic conditions. It was considered that O and oxidized cytochrome c compete with one another as H acceptors in the xanthine oxidase system. The cytochrome c of heart-muscle prepn. was found to be reduced by hypoxanthine in the presence of purified milk xanthine oxidase more slowly than the purified, extracted pigment. Phosphate, glyoxaline and glycine buffers, pH 7.3, and NaCl and KC1 inhibited the rate of reduction of cytochrome c by hypoxanthine and xanthine oxidase considerably. Phosphate buffer, pH 7.3, 3 x 10-3 [image], inhibited the anaerobic reduction by 44%. The possibility that reduced xanthine oxidase is not oxidized directly by oxygen in animal tissues was discussed.