STIMULATION OF OXIDATIVE-PHOSPHORYLATION BY ELECTROPHORETIC K+ ENTRY ASSOCIATED TO ELECTRONEUTRAL K+ H+ EXCHANGE IN YEAST MITOCHONDRIA/

The effect of the addition of KCl, at constant osmolarity, was investi gated on oxidative phosphorylation in isolated yeast mitochondria. KCl stimulated both respiration and ATP synthesis rates without changing the ATP/O ratio. KCl did not change the relationships between respirat ion rates and the protonmotive force. Since the K+/H+ exchange activit y was active under these conditions, the stimulatory effect of respira tion could be explained by the net proton entry caused by the electrop horetic K+ entry/electroneutral K+/H+ exchange cycle. On the other han d, K+ entry stimulated phosphate accumulation and transport under non- phosphorylating conditions and decreased the kinetic control by phosph ate transport under phosphorylating conditions. Additionally, the stim ulation of ATP synthesis strongly depended on the activity of phosphat e transport. Taken together, these data showed that electrophoretic K-entry and electroneutral K+/H+ exchange occurred in phosphorylating y east mitochondria but did not promote any uncoupling between respirati on and ATP synthesis.