Incorporation of mitochondrial L-glycerol-3-phosphate dehydrogenase into liposomes; effect of sodium oleate and calcium ions

FAD-linked L-glycerol-3-phosphate dehydrogenase purified from liver mitochondria of hyperthyroid rats was incorporated into unilamellar phospholipid liposomes. The incorporation influenced both Vmax,app and Km,app values of the enzyme for its substrate, L-glycerol 3-phosphate. The Km,app for the electron acceptor remained unchanged with a simultaneous slight enhancement of the corresponding Vmax,app value. The steady-state fluorescence anisotropies of the fluorescein isothiocyanate and trimethylammoniumdiphenylhexatriene labels were affected by sodium oleate and calcium ions in the case of both solubilized and liposome-incorporated L-glycerol-3-phosphate dehydrogenase. These results indicate that calcium ions cause a significant alteration of the enzyme conformation. Sodium oleate (used as a model of free fatty acids), besides its direct action on the enzyme itself, affects the enzyme indirectly as well, via alteration of the physical properties of the membrane.