Interactions between cyclic AMP-dependent protein phosphorylation and lipid transmethylation reactions in isolated porcine cardiac sarcolemma.

Premethylation of purified porcine cardiac sarcolemma (SL) in the presence of 0.15, 10 and 150 microM S-adenosyl-L-methionine (AdoMet) did not change the phosphorylation of SL proteins catalyzed either by intrinsic cyclic AMP-dependent protein kinase (cAK) or by added catalytic (C) subunit of this enzyme. On the other hand, membrane exhibited increased lipid methyltransferase activity after preincubation with MgATP and C subunit. Prephosphorylation of membranes stimulated the total [3H]-methyl incorporation into SL lipids assayed at 0.15 microM [3H]AdoMet due to an enhancement of Vmax and without changes in the Km value for AdoMet. Analysis of the methylated lipid products revealed an increased methyl group incorporation into a nonpolar lipid fraction whereas phosphatidylethanolamine-N-methylation was not affected by phosphorylation. The results suggest that the cyclic AMP-mediated signal transduction at the level of cardiac SL is not affected by methylation-induced modifications of the membrane lipid microdomains. On the other hand, an intrinsic SL lipid methyltransferase activity is apparently not related to the N-methylation of phospholipids, is modulated by cyclic AMP-dependent protein phosphorylation.