title: Evidence that the enzymes involved in the methylation of phosphatidylethanolamine are on the external side of the microsomal vesicles.
abstract: The topology of the phosphatidylethanolamine (PE)-N-methyltransferase(s) on rat liver microsomes has been studied. The activity for the conversion of PE to phosphatidylcholine decreased by 50% after 2 min of exposure of the microsomes to trypsin and was virtually eliminated with 15 min. When exogenous monomethyl-PE or dimethyl-PE were incubated with microsomes, the formation of dimethyl-PE and phosphatidylcholine were also eliminated as a result of trypsin digestion. During the experiments the microsomes remained intact, since the latency of the mannose-6-phosphate phosphohydrolase remained approx. 90%. It is concluded that the active site(s) of the enzyme(s), or portions of the enzyme(s) indispensable to its activity, are present at the cytosolic side of the microsomes.
mesh_terms: D000818:Animals; D005260:Female; D008780:Methyltransferases / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology* / Q000648:ultrastructure; D010713:Phosphatidylcholines / Q000378:metabolism; D050918:Phosphatidylethanolamine N-Methyltransferase; D010714:Phosphatidylethanolamines / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D014357:Trypsin / Q000378:metabolism
chemical_list: D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C032000:phosphatidyl-N-monomethylaminoethanol; C026508:phosphatidyldimethylethanolamine; D008780:Methyltransferases; D050918:Phosphatidylethanolamine N-Methyltransferase; D014357:Trypsin