An oligomycin-resistant adenosine triphosphatase and its effects on cellular growth, mitochondrial oxidative phosphorylation and respiratory proton translocation in Saccharomyces cerevisiae

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Abstract
Mutations at the OLI1 or OLI2 loci of mitochondrial DNA in S. cerevisiae are associated with a diminished growth rate in nutritionally suboptimal cultures supplemented with an oxidizable C source. In the case of mutant .**GRAPHIC**. (OLI1) there is a 35% loss of mitochondrial protein during fractionation in vitro, suggesting that the mutationally altered ATPase confers some instability on the mitochondrial membrane. The possibility is discussed that this reflects an unstable mitochondrial population in vivo, leading to the observed growth deficiency. Mitochondria from mutant .**GRAPHIC**. at the OLI1 locus show a relatively oligomycin-resistant State-3 respiration, but the same ADP/O and respiratory-control quotients as the isonuclear wild-type. A slightly lowered QO2 [oxygen quotient] with NADH-linked substrates was observed and is discussed. For both strains the apparent H+/O ratios were close to 4 with pyruvate, ethanol and .alpha.-oxoglutarate, but consistently lower with succinate and citrate. For each substrate a characteristic t1/2 (time for half-decay of the transmembrane pH differential) range was found, consistent with the view that the substrates effectively carry the protons back across the membrane. As expected, H+/O ratios were independent of t1/2 for all substrates, with the exception of .alpha.-oxoglutarate in the case of the wild-type, where an inverse correlation was found. The lack of this correlation in the case of the mutant was the only apparent difference in the translocation parameters observed. A hypothesis relating this to the functioning of the oligomycin-resistant ATPase is proposed.

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