Abstract
The proton-translocating, plasma membrane ATPase was purified from tomato roots. At the final stage of purification approximately 80% of the protein was found in a single band with an apparent molecular weight of 90 kilodaltons. Cross-linking studies indicated that the ATPase normally exists as a trimer of catalytic subunits. No evidence was found for any additional subunits. The pH optimum for ATP hydrolysis by the purified protein was 6.5. Activity was stimulated by K(+), especially at low pH, and inhibited by vanadate, N,N'-dicyclohexylcarbodiimide, and diethylstilbestrol; nitrate was weakly inhibitory. Activity was stimulated by lysolecithin but inhibited by sonicated phospholipids. The inhibition by lipids could be prevented if octylglucoside was added with the lipids; the combination of octylglucoside and lipids actually stimulated activity. The purified protein could be reconstituted into liposomes and catalyzed ATP-dependent, vanadate-sensitive proton translocation.