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

The activity of MgATPase (EC 3.6.1.35) and NADH-ferricyanide oxidoreductase was studied in plasma membrane vesicles purified from soybean (Glycine max L. cv. Williams) hypocotyls by aqueous polymer two-phase partitioning. The enzyme activities were measured at 21 degrees C in the absence and presence of Triton X-100 and in the presence of varying concentrations of sucrose between 10 mM and 1 M. In the absence of Triton X-100, both enzyme activities decreased with increasing sucrose concentrations. However, the sucrose dependent patterns were very different. In the presence of 0.015% (w/v) Triton X-100, the MgATPase and the NADH-ferricyanide oxidoreductase activities remained constant below and sharply decreased above 0.3 M and 0.5 M sucrose, respectively. It is concluded that (a) the latency of both enzyme activities depended on the concentration of sucrose, (b) the latency of MgATPase was less variable with sucrose concentration than that of NADH-ferricyanide oxidoreductase, and (c) the NADH-ferricyanide oxidoreductase activity is present on both sides of the plant plasma membrane.