PHOSPHOLIPID METABOLISM IN INTACT AND MODIFIED ERYTHROCYTE MEMBRANES

Abstract

Erythrocyte membranes incorporated labeled phosphate from γ-adenosine triphosphate (AT32P) into phosphatidic acid and the polyphosphoinositides. Inositol-3H and palmitate-14C were also incorporated into the phospholipids but α-glycerophosphate-32P was not. The incorporation of γ-AT32P into phospholipids was increased when the erythrocyte ghosts were incubated in hypotonic media which lysed the cells. Lysis had little or no effect on the incorporation of inositol-3H and palmitate-14C into the phospholipids. If erythrocyte membranes were prepared in 1 mM ethylenediaminetetraacetate (EDTA), instead of 1 mM MgCl2, then the tonicity of the incubating medium did not influence the incorporation of γ-AT32P into the phospholipids. Erythrocyte ghosts, prepared by lysis in water, EDTA, or 1 mM calcium, lead, mercury, zinc, or cadmium, failed to reconstitute when placed in isotonic medium, inasmuch as they did not retain potassium against a chemical gradient. Ghosts prepared by lysis in 1 mM magnesium, barium, or strontium could be reconstituted. Ghosts which failed to reconstitute incorporated more labeled phosphate from γ-AT32P into the phospholipids than did intact or reconstituted ghosts. The larger incorporation of labeled phosphate by leaky ghosts was not due to a greater entrance of γ-AT32P into those cells. Primaquine phosphate and digitonin, at concentrations which are known to cause cells to form smaller vesicles or to lyse cells by removing cholesterol, did not increase the incorporation of labeled phosphate into the phospholipids. It is suggested that the increased metabolism of phospholipids may be involved in a membrane repair mechanism.