Abstract
The transmethylation of phosphatidylethanolamine (PE) to phosphatidylcholine (PC) was studied in rat heart sarcolemmal membrane. Kinetically, three apparent K sub(m) values for S-adenosyl-L-methionine (AdoMet) were obtained when the total ( super(3)H)methyl groups incorporation into the phospholipids was examined in the presence of 0.01-250 mu M AdoMet. Under optimal conditions, the activities of all three methyltransferase sites were linear for at least 30 min of incubation and the sensitivity to the inhibitory effect of S-adenosyl-L-homocysteine was different for each site. Addition of exogenous PMME and PDME as substrates enhanced the synthesis of the corresponding methylated products by 3-5-fold and 3-8-fold, respectively. In contrast, exogenous PE failed to increase methyltransferase activity. These results provide evidence for the existence of three distinct methyltransferase active sites in rat heart sarcolemma.