Studies on Xanthine Oxidase

Abstract

Out of 35 substances tested, using the methylene blue technique, the only ones oxidized by the xanthine oxidase of milk were: hypoxanthine, xanthine, aldehydes, and possibly ade-nine. The following can act as H acceptors in oxidizing hypoxanthine in presence of the xanthine oxidase: methylene blue, thionine, guaiacum blue, all Clark''s "reduction-potential indicators," oxygen, H2O2, nitrates, dinitrobenzene, picric acid, permanganate, iodine, alloxan, and quinone. The oxidase shows a high degree of specificity towards the H donator, but none at all towards the H acceptor. Caution must be exercised in the interpretation of results obtained by the application of Clark''s oxidation-reduction indicators to biological systems.