Role of sulfhydryl groups in phospholipid methylation reactions of cardiac sarcolemma.
The effect of reagents that modify sulfur-containing amino acid residues in the phosphatidylethanolamine N-methyltransferase was studied in the isolated rat cardiac sarcolemma by employing S-adenosyl-L-[methyl-3H]methionine as a methyl donor. Dithiothreitol protected the sulfhydryl groups in the membrane and caused a concentration- and time-dependent increase of phospholipid N-methylation at three different catalytic sites. This stimulation was highest (9-fold) in the presence of 1 mM MgCl2 and 0.1 microM S-adenosyl-L-[methyl-3H]methionine at pH 8.0 (catalytic site I), and was associated with an enhancement of Vmax without changes in Km for the methyl donor. Thiol glutathione was less stimulatory than dithiothreitol; glutathione disulfide inhibited the phosphatidylethanolamine N-methylation by 50%. The alkylating reagents, N-ethylmaleimide and methylmethanethiosulfonate, inhibited the N-methylation with IC50 of 6.9 and 14.1 microM, respectively; this inhibition was prevented by 1 mM dithiothreitol. These results indicate a critical role of sulfhydryl groups for the activity of the cardiac sarcolemmal phosphatidylethanolamine N-methyltransferase and suggest that this enzyme system in cardiac sarcolemma may be controlled by the glutathione/glutathione disulfide redox state in the cell.
Vetter
R
R
Division of Cardiovascular Sciences St. Boniface General Hospital Research Centre, Winnipeg, Canada.
Dai
J
J
Mesaeli
N
N
Panagia
V
V
Dhalla
N S
NS
D000818:Animals; D002458:Cell Fractionation; D004229:Dithiothreitol / Q000494:pharmacology*; D006352:Heart Ventricles; D007700:Kinetics; D008297:Male; D008563:Membrane Lipids / Q000378:metabolism*; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D010743:Phospholipids / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012436:S-Adenosylmethionine / Q000378:metabolism; D012508:Sarcolemma / Q000378:metabolism* / Q000648:ultrastructure; D013438:Sulfhydryl Compounds / Q000378:metabolism
D008563:Membrane Lipids; D010743:Phospholipids; D013438:Sulfhydryl Compounds; D012436:S-Adenosylmethionine; D008780:Methyltransferases; D004229:Dithiothreitol