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

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