Disulfiram Inhibition of the Alternative Respiratory Pathway in Plant Mitochondria

Disulfiram (tetraethylthiuram disulfide) was found to be a potent and selective inhibitor of the alternative respiratory path of plant mitochondria. The onset of inhibition by disulfiram takes several minutes and the inhibition is not readily reversed by washing, nor by metal ions. By contrast, thiols such as dithiothreitol not only reverse, but also prevent, disulfiram inhibition. Inhibition by disulfiram and by hydroxamic acids are not mutually exclusive. Structural analogs of disulfiram are far less potent inhibitors, with the exception of bisethyl xanthogen. Inhibition is due to disulfiram, per se, and not to its reduction product, diethyldithiocarbamate, a powerful chelator. Accordingly, the inhibitory effect of disulfiram is considered to involve the formation of mixed disulfides with one or more sulfhydryl groups in the alternative path. Disulfiram does not act as an electron sink diverting electron flow from oxygen.Disulfiram inhibition was observed only with isolated mitochondria or submitochondrial particles. In intact cells or tissues either a failure to absorb disulfiram, or its dissipation in the cytosol, precludes inhibition. In vitro, bovine serum albumin reduces disulfiram inhibition by complexing free inhibitor.The binding of (35)S-disulfiram by cyanide-resistant mitochondria displays the same kinetics as disulfiram inhibition. A comparison was made of (35)S-disulfiram binding by cyanide-sensitive and cyanide-resistant potato mitochondria. Cyanide-resistant mitochondria were obtained from ethylene-treated potato tubers. Incorporation of label proved essentially the same in both types of mitochondria, suggesting that the disulfiram-sensitive component of the alternative path is present in untreated potato tubers, and is not induced by ethylene.