Influence of enzymatic phospholipid cleavage on the permeability of the erythrocyte membrane. II. Protein-mediated transfer of monosaccharides and anions.

In order to investigate the influence of membrane lipids on transport via the protein domain of the erythrocyte membrane, a number of facilitated diffusion processes was studied by tracer flux techniques in whole cells after cleavage of up to 65% of the phosphatidylcholine or the sphingomyelin by phospholipase A2 from Naja naja or bee venom, or by sphingomyelinase, respectively. The mediated fluxes of L-arabinose, which is transported by the glucose carrier, and of L-lactate, which uses a specific monocarboxylate carrier, were markedly inhibited by cleavage of either phosphatidylcholine or sphingomyelin. These phospholipid dependencies are in line with earlier data on cholesterol dependencies (Deuticke, B. (1977) Rev. Physiol. Biochem. Pharmacol. 78, 1-97). They can only in part be explained by changes of membrane fluidity. More specific interactions of the degradation products with the carrier proteins seem also to play a role. Sulfate and oxalate transfer, which proceed via the inorganic anion-exchange system, are essentially unaffected by cleavage of phosphatidylcholine and less sensitive to sphingomyelin cleavage than the two other processes. This also agrees with earlier data on cholesterol independency of sulfate transfer. The inorganic anion-exchange protein thus seems to be less dependent on the surrounding lipids in its conformation and its mode of action than the two other carriers.