6-KETOCHOLESTANOL ABOLISHES THE EFFECT OF THE MOST POTENT UNCOUPLERS OF OXIDATIVE-PHOSPHORYLATION IN MITOCHONDRIA

The effect of a keto-derivative of cholesterol, namely, 6-ketocholesta nol (5 alpha-cholestan-3 beta-ol-6-one; kCh) on the uncoupling of oxid ation and phosphorylation by various uncouplers was studied in rat hea rt mitochondria. kCh was found to completely abolish the uncoupling ef fect (the increase in the respiration rate under the respiratory contr ol conditions and the decrease in the membrane potential) caused of FC CP, CCCP and SF6847 and partially by TTFB at low concentrations of unc ouplers. It was without effect on the uncoupling by PCP, DNP and palmi tate. Carboxyatractylate, a specific inhibitor of the ADP/ATP-antiport er, was shown to almost completely abolish the uncoupling induced by p almitate and partially by low concentration of TTFB, PCP and DNP. Effe cts of high concentrations of all these uncouplers as well as of any c oncentrations of gramicidin proved to be kCh- and carboxyatractilate-i nsensitive. The data are discussed in terms of the hypothesis on the p rotein-mediated mechanism of the protonophorous uncoupling.