INCREASED CA2+-ATPASE ACTIVITY ASSOCIATED WITH METHYLATION OF PHOSPHOLIPIDS IN HUMAN-ERYTHROCYTES

Ca2+-ATPase activity in human erythrocytes is increased by the enzymatic methylation of membrane phospholipids. Erythrocyte membranes incubated in the presence of the methyl donor, S-adenosyl-L-methionine, demonstrate increased Ca2+ stimulated ATP hydrolysis, increased [45Ca2+] efflux from erythrocyte ghosts and synthesis of phosphatidyl-N-monomethylethanolamine. The increase in Ca2+-ATPase activity is due to an increase in Vmax, and not due to changes in affinity for ATP or Ca2+. The concentration of S-adenosyl-L-methionine needed to stimulate Ca2+-ATPase closely matches that needed for the methylation of phosphatidylethanolamine. Both the stimulation of Ca2+-ATPase and the methylation of phospholipids are inhibited by the methyltransferase inhibitor, S-adenosyl-L-homocysteine. Membrane fluidity is increased by phospholipid methylation, which may be the mechanism for Ca2+-ATPase stimulation. © 1979.