On the relationship between ATPase and fusicoccin binding capacity of crude and partially-purified microsomal preparations from maize coleoptiles

Abstract

The behaviour of ATPase activity and of in vitro binding of fusicoccin (FC) in particulate and partially solubilised microsomal preparations from maize coleoptiles was investigated. In the particulate system diethylstilbestrol (DES) and Cercospora beticola toxin (CBT) parallely inhibited FC binding and dicyclohexy-carbodiimide (DCCD)-sensitive ATPase activity. Among the solubilising treatments sodium deoxycholate (DOC) and trypsin solubilised equal fractions of bound FC and of ATPase activity, while sodium perchlorate, incubation at pH 8.8 and EDTA in the absence of Mg 2+ were much more active in solubilising the ATPase than the bound FC. Disc gel electrophoresis of the microsomal perchlorate extract led to the separation of the FC-receptor complex from the ATPase activity. The sensitivity of ATPase to DCCD and to DES was not influenced by solubilisation with DOC, but was almost completely suppressed by that with perchlorate, while solubilisation by incubation at pH 8.8 suppressed the sensitivity to DCCD but not that to DES. These data suggest the presence in the plasma membrane of a multi-unit ATPase system coordinating distinct components, some of which would be able to interact with FC and with the inhibitors in such a way as to influence the activity of the catalytic sub-unit.