Calmodulin regulation of phospholipid and fatty acid methylation by rat liver microsomes

The addition of micromolar Ca2+ in the presence of ATP (10 microM) to rat liver microsomes stimulates phospholipid methylation and the formation of fatty acid methyl esters. Our data indicate that calmodulin mediates the effect of Ca2+ on both phospholipid and fatty acid methylation. This evidence includes: 1) chlorpromazine, an inhibitor of Ca2+ effects mediated through calmodulin, prevented the activation by Ca2+ plus ATP of the methylation reactions; 2) isolation of the microsomes in the presence of ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (5 mM), to remove endogenous calmodulin also prevented Ca2+ plus ATP stimulation of both phospholipid and fatty acid methylation; 3) the addition of exogenous calmodulin to microsomes isolated in the presence of 5 mM ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid restored Ca3+ plus ATP stimulation of both classes of lipids: and 4) pre-incubation of liver microsomes with an antiserum against calmodulin prevented the activation of lipid methylation by Ca2+ plus ATP.