Effect of Cations on the Plasma-membrane-bound ATPase from the Yeast Metschnikowia reukaufii

Abstract

SUMMARY: Plasma membranes from osmotically lysed protoplasts of Metschnikowia reukaufii were concentrated 21- to 26-fold (using the recovery of [3H]dansyl chloride and ATPase activity at pH 6.5, as criteria). The contamination by mitochondria was approximately 10%. The plasma membrane ATPase was stimulated by K+ by up to 350% at pH 6.5; Na+ had a lesser effect, whereas Li+ had none. The stimulation by K+ was independent of Cl−, NO3 − or CO2 3 − as accompanying anions. The pH optimum of the ATPase was narrowed in the presence of 80 mM-KC1 to a distinct peak at pH 6.5. Under these conditions nucleoside triphosphates other than ATP were hydrolysed at rates less than 5% of that with ATP, and the K m of the ATPase for ATP was lowered from 1.3 to 0.6 mM. Orthovanadate (40 μM) and oligomycin (5 μg ml−1) inhibited the plasma membrane ATPase by 65% and by 20%, respectively. In contrast, the ATPase activity of the mitochondrial fraction had a sharp optimum at pH 8.5 and was not stimulated by added K+.