Energy Dependent Bivalent Cation Translocation in Rat Liver Mitochondria

Abstract

1 The initial rates of Ca++, Sr++, Mn++, and Ba++, accumulation into rat liver mitochondria were measured by a cation sensitive indicator, murexide. 2 The rates of oxidation of cytochrome b induced by these bivalent cations were determined. 3 The presence of Mn++ retards the Ca++ induced cytochrome b oxidation rate, while the presence of Ca++ accelerates the Mn++ induced cytochrome b response. 4 Praseodymium (Pr+++) inhibits specifically at a concentration less than 0.1 nmole per mg protein the reactions of Ca++, Sr++, Ba++ and Mn++ with the mitochondrial membrane and their accumulation into the mitochondria. The Mn++ translocation was, however, stimulated at a concentration of 0.02 nmole praseodymium per mg protein. 5 Mg++ and K+ have an inhibitory effect on the bivalent cation translocation. In the case of Mn++, however, Mg++ and K+ have a slight activating effect at low concentrations.