Phospholipid dependence of the Hymenolepis diminuta mitochondrial NADPH:NAD transhydrogenase

The mitochondrial, membrane-associated, nonenergy -linked NADPH:NAD transhydrogenase of adult Hymenolepis diminuta exhibited a phospholipid dependence. This lipid dependence was suggested when mitochondrial membranes were subjected to organic solvent or phospholipase treatments. Although hexane extraction of lyophilized membranes enhanced transhydrogenase activity, subsequent aqueous acetone extraction significantly inhibited the transhydrogenase. An acetone/water-dependent extraction of phospholipids was reflected in the phosphorus content of released material. Incubation of mitochondrial membranes with phospholipase A2 or C markedly reduced transhydrogenase activity, and phospholipase A2 treatment resulted in the greater reduction in activity. The mitochondrial, membrane-associated, NADH-utilizing oxidase and fumarate reductase activities were diminished significantly by hexane as well as phospholipase treatments. Phospholipase A2 caused the greater inhibition of the NADH-utilizing systems. Thus, in contrast to the transhydrogenase, neutral lipids and phospholipids apparently were required by the electron transport-coupled activities. The transhydrogenase activity of organic solvent- or phospholipase-treated membranes was not stimulated effectively by phospholipid addition. However, phospholipid-dependent stimulation of transhydrogenase was accomplished employing a partially lipid-depleted preparation of the enzyme obtained by detergent treatment and ammonium sulfate precipitation. Of the phospholipids tested, only phosphatidylcholine significantly stimulated transhydrogenase activity. The stimulation noted with phosphatidylcholine was not duplicated by cholate or deoxycholate.