INTERRELATIONSHIPS BETWEEN ALDEHYDE DEHYDROGENASE OF ACINETOBACTER-CALCOACETICUS AND MEMBRANE-LIPIDS .2. RECONSTITUTION IN ARTIFICIAL MEMBRANE-VESICLES

Purified aldehyde dehydrogenase (NADP+-dependent) of intracytoplasmic membranes of Acinetobacter calcoaceticus could be incorporated from micelles formed during the purification procedure into liposomal membranes. Both the cholate dilution method and the ultrasonication method were suitable to produce enzyme liposomes. In unilamellar liposomes produced by phosphatidyl choline, the enzyme activity decreased to 1% (or less) of the original activity. In contrast, about 10% of the original activity could be preserved in unilamellar liposomes prepared from bacterial phospholipids. The destruction of the enzyme liposomes induced by detergents (lauroyl sarcosinate) was followed by measuring the wavelength dependence of turbidity, which allowed us to draw conclusions on size and stability of the particles in the suspension. In addition these measurements demonstrated that decanal and NADP+ did not destroy the liposomal structure at concentrations necessary for the determination of enzyme activity. The liposomal enzyme was inactivated to a lesser degree by proteinase K than the micellar enzyme. Both phospholipase A2 and D inactivated the enzyme incorporated into the liposomal membranes to about 50%. After treatment with phospholipase A2, the enzyme could be reactivated by bacterial phospholipids. After treatment with phospholipase D, no reactivation was possible by bacterial phospholipids.