MODULATION OF HYDROLYTIC ACTIVITY OF PLASMALEMMA H-ATPASE AT VARIOUS TEMPERATURES BY K+-DIFFUSION POTENTIAL DELTA-PSI()

Influence of valinomycin-induced K+-diffusion potential (Delta psi(D)) on hydrolytic activity of H+-ATPase at 24 degrees C and 6 degrees C w as studied on plasma membranes (PM) isolated from pumpkin (Cucurbita p epo L.) stem cells. Shifting Delta psi(D) from 0 to 41 and 87 mV accel erated hydrolysis of ATP. This stimulation by Delta psi(D) was manifes ted in quantitative rather than qualitative changes, most prominent at an early stage after ATP addition (from 0 to 0.5 min). It was likely related to a conformational mobility of H+-ATPase. Restriction of conf ormational mobility of the enzyme at 6 degrees C was accompanied by an increase in the potential-dependence of ATP hydrolysis. The continual diffusion model was employed to discuss the potential-dependence of A TP hydrolysis in relation to conformational mobility of H+-ATPase in t he membrane. We conclude that Delta psi(D) has an ordering effect on A TP hydrolysis.