Revertant of the yeast Schizosaccharomyces pombe with modified alpha subunits of mitochondrial ATPase-ATPsynthase: impaired nucleotide interactions with soluble and membrane-bound enzyme.

A partial revertant from a mutant with modified alpha subunits of mitochondrial ATPase-ATPsynthase has been obtained for the first time from the yeast Schizosaccharomyces pombe. The purified F1 contains a lower amount of endogenous nucleotides as compared to the wild-strain enzyme. In contrast to the wild-type, the F1 ATPase activity from the revertant does not exhibit bicarbonate-sensitive negative cooperativity. The revertant Michaelis constant for Mg-ATP is very similar to that of normal F1 in the presence of bicarbonate while the Vm is slightly lower. The revertant enzyme is much less sensitive to inhibitions by ADP and by azide. It is proposed that the lack of negative cooperativity of revertant F1 ATPase activity is due to lower affinity for ADP, the release of which is no longer the rate-limiting step.