NADH-FERRICYANIDE OXIDOREDUCTASE IS PRESENT ON BOTH SIDES OF PLANT PLASMA-MEMBRANE

The activity of MgATPase (EC 3.6.1.35) and NADH-ferricyanide oxidoredu ctase was studied in plasma membrane vesicles purified from soybean (G lycine max L. cv. Williams) hypocotyls by aqueous polymer two-phase pa rtitioning. The enzyme activities were measured at 21 degrees C in the absence and presence of Triton X-100 and in the presence of varying c oncentrations of sucrose between 10 mM and 1 M. In the absence of Trit on X-100, both enzyme activities decreased with increasing sucrose con centrations. However, the sucrose dependent patterns were very differe nt. In the presence of 0.015% (w/v) Triton X-100, the MgATPase and the NADH-ferricyanide oxidoreductase activities remained constant below a nd sharply decreased above 0.3 M and 0.5 M sucrose, respectively. It i s concluded that (a) the latency of both enzyme activities depended on the concentration of sucrose, (b) the latency of MgATPase was less va riable with sucrose concentration than that of NADH-ferricyanide oxido reductase, and (c) the NADH-ferricyanide oxidoreductase activity is pr esent on both sides of the plant plasma membrane.