Evidence for three catalytic sites in heart sarcolemmal phospholipid N-methylation.
Conversion of phosphatidylethanolamine to phosphatidylcholine through sequential transmethylation reactions was studied in rat cardiac sarcolemmal membrane prepared by the hypotonic shock-LiBr treatment method. Three catalytic sites were identified on the basis of their requirement for divalent cations and kinetic parameters. Site I (Km = 0.1 +/- 0.01 microM) required Mg2+ as a cofactor and had a very high affinity for [3H]-S-adenosyl-L-methionine (AdoMet). Sites II (Km = 2.9 +/- 0.3 microM) and III (Km = 112 +/- 6 microM) did not require any divalent cation and showed comparatively lower affinities for AdoMet. Developmental-related differences were found to exist among these three catalytic sites when phospholipid methylation was carried out in 1- to 12-week-old rats. The results suggest that three distinct methyltransferase sites are involved in cardiac sarcolemmal phospholipid methylation.
D000818:Animals; D002384:Catalysis; D055598:Chemical Phenomena; D002621:Chemistry; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D008297:Male; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology*; D010713:Phosphatidylcholines / Q000096:biosynthesis*; D010714:Phosphatidylethanolamines / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012436:S-Adenosylmethionine / Q000378:metabolism; D012508:Sarcolemma / Q000201:enzymology*
D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C032000:phosphatidyl-N-monomethylaminoethanol; C026508:phosphatidyldimethylethanolamine; D012436:S-Adenosylmethionine; D008780:Methyltransferases; D008274:Magnesium