Interaction of human cytoplasmic aldehyde dehydrogenase E1 with disulfiram

Two equivalents of symmetrically labeled [14C]-disulfiram (tetraethylthiuram disulfide, Antabuse) interact with human liver cytoplasmic aldehyde dehydrogenase (ALDH) E1 (E.C. 1.2.1.3) inhibiting ca. 90% of total catalytic activity. Inhibition occurs without labeling of the enzyme but is associated with disappearance of four SH groups per molecule of enzyme. Inhibition is reversible by treatment with 2-mercaptoethanol suggesting that disulfiram oxidizes vicinal enzyme SH groups to disulfides. The radioactivity from disulfiram is recovered as diethyldithiocarbamate. SDS gel electrophoresis indicates that vicinal SH groups involved in the interaction with disulfiram occur on the same subunits. This is also consistent with the fact that introduction of disulfide bonds by disulfiram is not accompanied by a major conformational change as evidenced by fluorescence polarization or circular dichroism. Experiments with o-iodosobenzoate suggest the presence of a third SH group in the vicinity of the two interacting with disulfiram. Inhibition of aldehyde dehydrogenase by disulfiram is not easily reversible by glutathione which might explain why new protein synthesis is required to regain enzyme activity in vivo.