Hepatic Aldehyde Oxidase

Previous reports on rabbit liver aldehyde oxidase described the purification and some properties of the enzyme (1) and the differential inhibition of electron transfer to various acceptors (2). The latter study furnished evidence for the participation of several electron carriers in the internal electron transport sequence of the enzyme. The present communication summarizes the results of studies designed to elucidate the nature of the substrate-binding site of hepatic aldehyde oxidase and the manner of interaction with substrate. In 1946, Knox (3) presented evidence for the identity of the quinine oxidase of rabbit liver with the aldehyde oxidase of the same tissue. The ability of a crude preparation of the enzyme to catalyze oxidation of a group of aldehydes as well as that of diverse nitrogen-containing aromatic heterocyclic compounds was evident from these studies. The same dual specificity is also exhibited by the highly purified enzyme (1). Subsequently, the ability of the enzyme to oxidize phenazine methosulfate was also demonstrated (4). In the present studies, the substrate specificity of the enzyme has been further investigated. In addition, the inhibition, by several compounds, of enzyme-substrate interaction has been studied. The results suggest the presence of a reactive sulfhydry1 group and of molybdenum at the substrate-binding site of the enzyme. Comparative studies have also been made with the somewhat similar xanthine oxidase.