title: Differential membrane protein carboxyl-methylation of intact human erythrocytes by exogenous methyl donors.
abstract: The patterns of membrane protein carboxyl-methylation by protein methylase II (S-adenosylmethionine: protein-carboxyl O-methyltransferase, EC 2.1.1.24) in intact human erythrocytes were shown to differ markedly whether the methyl donor, S-adenosyl-L-[methyl-3H]methionine, was supplied exogenously or formed intracellularly via exogenously added L-[methyl-3H]methionine. The differences include the following. (1) The methylation of cytoskeletal components (band 2.1 and 4.1) occurs only in the case of the L-[methyl-3H]methionine-labelled cells. (2) The methionine-mediated methylation was much less sensitive to S-adenosyl-L-homocysteine inhibition than the adenosylmethionine-mediated methylation (22% versus 95% inhibition at 10 microM). (3) The membrane protein methylation mediated by exogenous adenosylmethionine and methionine differed markedly in their alkali labilities; at pH 6.0, 30% of the adenosylmethionine-mediated protein methyl esters were hydrolysed after 30 min (37 degrees C) while the methionine-mediated esters were stable. At pH 7.4, the respective labilities were 60% and 30% for the 30 min incubation. To explain these results, a possible involvement of cytoskeletal structure associated with the intact erythrocyte is discussed.
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D008565:Membrane Proteins / Q000097:blood*; D008715:Methionine / Q000097:blood*; D008745:Methylation; D011497:Protein O-Methyltransferase / Q000097:blood; D012435:S-Adenosylhomocysteine / Q000494:pharmacology; D012436:S-Adenosylmethionine / Q000097:blood*
chemical_list: D008565:Membrane Proteins; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D008715:Methionine; D011497:Protein O-Methyltransferase