High purity preparations of higher plant vacuolar H+-ATPase reveal additional subunits. Revised subunit composition

Abstract

A fast protein liquid chromatography procedure for purification of the V-type H+-ATPase from higher plant vacuolar membrane to yield near-homogeneous enzyme with a specific activity of 20-25 mumol/mg.min is described. When precautions are taken to ensure the quantitative recovery of protein before sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the preparation is found to be constituted of seven major polypeptides of 100, 67, 55, 52, 44, 32, and 16 kDa, respectively, and two minor components of 42 and 29 kDa. The 52-, 44-, and 32-kDa polypeptides do not cross-react with antisera raised to the 67- and 55-kDa subunits of the enzyme, and two independent sample preparation procedures yield the same apparent subunit composition. The additional polypeptides are not breakdown products or aggregates of the previously identified subunits of the ATPase. The ATPase of tonoplast vesicles is subject to MgATP-dependent cold inactivation, and the conditions for inactivation are identical to those for the bovine chromaffin granule H+-ATPase (Moriyama, Y., and Nelson, N. (1989) J. Biol. Chem. 264, 3577-3582). Cold inactivation is accompanied by the detachment of five major polypeptides of 67, 55, 52, 44, and 32 kDa from the membrane, and all five components co-migrate with the corresponding polypeptides of the purified ATPase upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The 100- and 16-kDa polypeptides of the ATPase are not removed from the membrane during cold inactivation, but the latter can be purified to homogeneity by chloroform:methanol extraction of the fast protein liquid chromatography-purified enzyme. It is concluded that the tonoplast H+-ATPase is constituted of 6-7 major polypeptides organized into a peripheral sector comprising the 67-, 55-, 52-, 44-, and 32-kDa components and an integral sector consisting of the 100- and 16-kDa polypeptides. The V-type H+-ATPase from animal endomembranes and higher plant vacuolar membranes therefore have remarkably similar subunit compositions and gross topographies.