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Membrane vesicles derived from the tonoplast of Beta vulgaris L. possess two predominant phosphohydrolase activities: a Cl(-)-stimulated, NO(3) (-)-inhibited ATPase, and a K(+)-stimulated, Na(+)-inhibited inorganic pyrophosphatase (PPase). The solubilization of tonoplast vesicles with 2% (w/v) Triton X-100 containing 4 millimolar MgCl(2) and 1 millimolar ethylenediamine tetracetic acid, as protectants, gives high yields of both the ATPase and PPase in soluble form. Chromatography of the solubilized membranes on Sephacryl-400 results in the separation of the two enzymes. The PPase and ATPase are purified 4- and 17-fold, respectively, with quantitative recovery. The separated enzymes show negligible activity towards the other's substrate and the separated PPase only hydrolyzes pyrophosphate. The separated enzymes show mineral ion requirements identical to those of the corresponding pump and hydrolytic activities in native tonoplast and both solubilized enzymes are subject to phospholipid activation.
Rea et al. (Thu,) studied this question.