STIMULATION OF THE CA2-ATPASE OF SARCOPLASMIC-RETICULUM BY DISULFIRAM()

Disufiram [bis(diethylthiocarbamoyl)disulphide] has been found to stim ulate reversibly the Ca2+-ATPase of skeletal muscle sarcoplasmic retic ulum. At pH 7.2, 2.1 mM ATP and 25 degrees C, ATPase activity was foun d to double on addition of 120 mu M disulfiram. Stimulation fitted to binding of disulfiram at a single site with a K-d of 61 mu M. Disulfir am had no effect on the Ca2+ affinity of the ATPase or on the rate of phosphorylation of the ATPase by ATP, but increased the rate of dissoc iation of Ca2+ from the phosphorylated ATPase (the transport step) and increased the rate of dephosphorylation of the phosphorylated ATPase. It also decreased the level of phosphorylation of the ATPase by P-i, consistent with a 7.5-fold decrease in the equilibrium constant of the phosphorylated to non-phosphorylated forms (E2PMg/E2P(i)Mg) at 80 mu M disulfiram. Disulfiram had no significant effect on the concentratio n of ATP resulting in stimulation of ATPase activity, suggesting that it does not bind to the empty nucleotide-binding site on the phosphory lated ATPase. Studies of the effects of mixtures of disulfiram and jas mone (another molecule that stimulates the ATPase) suggest that they b ind to separate sites on the ATPase.