THE ROLE OF PLASMA-MEMBRANE OXIDOREDUCTASE ACTIVITY IN PROTON TRANSPORT

Inside-out plasma membrane vesicles were obtained after partition of t he freeze/thawed right-side out vesicles from cucumber roots in a two phase system. A sidedness of the plasma membrane vesicles was determin ed by the latency of vanadate-sensitive ATPase and trypsin digestion o f the enzyme. In experiments with ferricyanide-loaded vesicles a low t ransplasma membrane electron transport with NADH as an electron donor was generated. However, introduction of Triton X-100 into the reaction medium increased the rate of NADH oxidation several times. During inc ubation with ATP of both unloaded vesicles and vesicles loaded with fe rricyanide, the decrease in acridine orange absorbance was observed. D CCD and sodium orthovanadate added to the reaction mixture diminished distinctly the changes of acridine absorbance. These results indicate that in vesicles the ATP-dependent H+ pump is active. Incubation of th e ferricyanide-loaded vesicles with NADH caused a small increase of ac ridine absorbance that was deteriorated in the presence of quinacrine. The contribution of the plasma membrane NADH-ferricyanide oxidoreduct ase in the H+ transport is discussed.