Characterization and Localization of the ATPase Associated with Pea Chloroplast Envelope Membranes

Abstract

Chloroplast envelope membranes isolated from P. sativum seedlings contain a Mg-ATPase activity (specific activity 50-175 nmol/min .cntdot. mg-1 protein). The ATPase had a broad pH optimum between 7.0 and 9.5. The activity was neither inhibited by oligomycin, N,N''-dicyclohexylcarbodiimide, ouabain or antibodies directed against chloroplast coupling factor 1; nor was the activity stimulated by monovalent cations. The ATPase was inhibited by vanadate, molybdate and adenylyl imidodiphosphate. The ATPase hydrolyzed a broad range of nucleoside triphosphates, but did not hydrolyze ADP, AMP or pyrophosphate. The Km for Mg-ATPase was 0.2 mM. The ATP was distinct from ADPase and pyrophosphatase activities also present in pea envelope membranes. The ATPase was located on the inner membrane of the envelope after resolution of inner and outer membranes by sucrose density gradient centrifugation.