The specificity of xanthine oxidase

Abstract

The evidence in the literature against identity of xanthine oxidase and the Schardinger enzyme was investigated but not substantiated. These enzymes have now apparently been proved identical, and the name Schardinger enzyme should be dropped. The specificity of the enzyme was studied with the following results. Four purines were added to the existing list of 5 activated by xanthine oxidase and the rates of their oxidation detd.: they are 8-hydroxypurine, 2:8-dihydroxypurine. 6-amino-2-hydroxypurine and 6-amino-8-hydroxypurine. The direct activation of the 2 aminopurines is proved, and of adenine confirmed, by demonstrating that previous deamination does not occur. Cozymase is destroyed by a nucleosidase in the enzyme preparation, but not, as stated in the literature, by xanthine oxidase itself. The destruction is independent of oxidation. A list of 35 aldehydes activated was compiled. Because formaldehyde and piperonal compete for the enzyme, it is suggested that only the one enzyme is concerned in the activation of all. Substances related to aldehydes[long dash]mannose, glucosone, gluconate. chloral hydrate, butyl chloral hydrate, paraldehyde[long dash]do not combine with the enzyme. Because all aldehydes so far tested (representing widely different members of the series) are activated, while related substances are not, it is concluded that in addition to purines all true aldehydes[long dash]but only true aldehydes[long dash]are activated.