NADH-ASCORBATE FREE-RADICAL AND NADH-FERRICYANIDE REDUCTASE ACTIVITIES REPRESENT DIFFERENT LEVELS OF PLASMA-MEMBRANE ELECTRON-TRANSPORT

Plasma membranes isolated from rat liver by two-phase partition exhibi ted dehydrogenase activities for ascorbate free radical (AFR) and ferr icyanide reduction in a ratio of specific activities of 1 : 40. NADH-A FR reductase could not be solubilized by detergents from plasma membra ne fractions. NADH-AFR reductase was inhibited in both clathrin-deplet ed membrane and membranes incubated with anti-clathrin antiserum. This activity was reconstituted in plasma membranes in proportion to the a mount of clathrin-enriched supernatant added. NADH ferricyanide reduct ase was unaffected by both clathrin-depletion and antibody incubation and was fully solubilized by detergents. Also, wheat germ agglutinin o nly inhibited NADH-AFR reductase. The findings suggest that NADH-AFR r eductase and NADH-ferricyanide reductase activities of plasma membrane represent different levels of the electron transport chain. The inabi lity of the NADH-AFR reductase to survive detergent solubilization mig ht indicate the involvement of more than one protein in the electron t ransport from NADH to the AFR but not to ferricyanide.