REGULATION OF ROSE CELL PLASMA-MEMBRANE ATPASE ACTIVITY BY GLUTATHIONE

In suspension-cultured rose cells (Rosa damascena Mill. cv. Gloire de Guilan) irradiated with UV-C, the concentration of oxidized glutathion e (GSSG) inside the cells increases, and the membrane potential decrea ses. Using purified plasma membrane vesicles, we show that GSSG irreve rsibly inhibits ATPase activity. Inhibition of the enzyme by cystine, p-chloromercuribenzoate (PCMB), p-chloromercuribenzene sulfonate, but not reduced glutathione or cysteine, is consistent with the interpreta tion that GSSG oxidizes thiol groups of the ATPase protein. In contras t to reports of results with other plant plasma membrane ATPases, N-et hylmaleimide (NEM) and diethylmaleate were not inhibitory, nor did NEM protect ATPase from inhibition by PCMB. ATPase protein was located on two-dimensional gel electropherograms using a specific antibody. NEM did protect the ATPase protein from the change in electrophoretic mobi lity caused by treatment with didansyl-L-cystine. We suggest that the ATPase protein contains two kinds of thiols, which have different reac tivities with NEM. Using purified right-side-out vesicles and inside-o ut vesicles, it was determined that GSSG inhibition of ATPase activity on the cytoplasmic side of the plasma membrane was stronger than that at the external side. We suggest that the inhibition of ATPase by GSS G is one of the mechanisms by which UV-C irradiation effects a long-te rm decrease in the membrane potential of rose cells.