Modifications of oxidative phosphorylations in mitochondria isolated from a mutant of Saccharomyces cerevisiae. Possible alterations of the phosphate transport.

Mutants of Saccharomyces cerevisiae were isolated which supported two unlinked nuclear mutations conferring thermosensitivity and cold sensitivity respectively, and a mitochondrial one conferring paromomycin sensitivity. Mitochondria isolated from such a mutant exhibited modifications of several phosphate-requiring functions: (a) kinetic parameters of the phosphate dependence of ATP synthesis were modified; (b) in the absence of phosphate the inner mitochondrial membrane exhibited a high proton leakage; (c) mutant mitochondria always exhibited a poor respiratory control and required tenfold more phosphate to reach a maximal state 3 of respiration; (d) phosphate transport, as measured by swelling experiments, was mersalyl-insensitive and, consequently, state 3 of the respiration and ATP synthesis remained less mersalyl-sensitive than in wild-type mitochondria. Analysis of the mitochondrial metabolism of diploid and segregant strains indicates that these modifications are related to the cryosensitive phenotype; however, at present, a cooperative effect of the mitochondrial mutation cannot be eliminated. It is proposed that the phosphate carrier itself or a regulatory element was modified.