ATPase activity of isolated plasma membrane vesicles of leaves of Elodea as affected by thiol reagents and NADH/NAD+ ratio

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Abstract
The goal of this study was to test the hypothesis that the plasma membrane‐bound ATPase activity is influenced by the redox poise of the cytoplasm. Purified plasma membrane vesicles from leaves of Elodea canadensis Michx. and E. nuttallii (Planch.) St. John were isolated using an aqueous polymer two‐phase batch procedure. The distribution of marker enzyme activities confirmed the plasma membrane origin of the vesicles. The vesicles exhibited NADH‐ferricyanide reductase activity, indicating the presence of a redox chain in the plasma membrane. The K+, Mg2+‐ATPase activity associated with these vesicles was inhibited by the sulfhydryl reagents N‐ethylmaleimide and glutathione (GSSG). Furthermore the activity was inhibited by NAD+. This inhibition by NAD+ was relieved by increasing the NADH/NAD+ ratio. The possibility that the ATPase activity is regulated by the cytoplasmic NAD(P)H/ NAD(P)+ ratio is discussed, as well as the role of a plasma membrane‐bound redox chain.