Detergent activity of NADH oxidase in vesicles derived from the plasmamembrane of Cucurbita pepo L.

In microsomes from Cucurbita hypocotyls a duroquinone (DQ) stimulated NADH oxidase was found which is strongly activated by addition of 0.01–0.1% Triton X-100. After density gradient centrifugation and polyethyleneglycol (PEG) fractionation this enzyme occurs in membranes carrying plasma membrane markers. Another NADH oxidase localized at the endoplasmic reticulum (e.r.) is not activated but inhibited by Triton. The data are consistent with closed and outside-out plasma membrane vesicles where the NADH site becomes accessible only after detergent permeabilization. A role of the enzyme in transmembrane transport of electrons and/or protons is discussed.