SOME PROPERTIES OF A FUNCTIONAL RECONSTITUTED PLASMALEMMA H-ATPASE ACTIVATED BY FUSICOCCIN()

Fusicoccin was shown to stimulate the ATP-driven, intravesicular acidi fication of liposomes reconstituted with crude fusicoccin receptors an d the H+-translocating ATPase, both solubilized from maize (Zea mays L .) plasma membrane. The present paper reports optimal conditions for d ual reconstitution and fusicoccin activation as well as the biochemica l characterization of the effect of fusicoccin on this system. Fusicoc cin stimulation of proton pumping was dependent on pH and fusicoccin c oncentration. Its specificity was demonstrated by the positive effect of two cotylenins that have a high affinity for fusicoccin receptors a nd by the negative response to 7,9-epideacetylfusicoccin, an inactive fusicoccin derivative. Kinetic measurements at different ATP concentra tions showed that fusicoccin increases the V(max) of the enzyme. Fusic occin stimulation of maize H+-ATPase was also maintained when receptor s from maize were substituted by those from spinach (Spinacia oleracea L.).