Evidence for an active site persulfide residue in rabbit liver aldehyde oxidase.

The reduction of aldehyde oxidase (EC 1.2.3.1) by the substrate W-methylnicotinamide under anaerobic conditions is a biphasic reaction. In the present work we present evidence that this behavior is due to the presence, in standard preparations, of active and inactive enzyme, the former being responsible for the fast reaction and differing from the latter by the presence of a persulfide group. It is also demonstrated that the earlier reported inactivation of the enzyme by cyanide is due to cyanolysis of this persulfide group.