Methyl Acceptors for Protein Methylase II from Human‐Erythrocyte Membrane

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Abstract
Membrane proteins from human erythrocytes were methylated with purified protein methylase II (S‐adenosylmethionine: protein‐carboxyl O‐methyltransferase, EC.2.1.1.24). The methylated proteins were analyzed by dodecyl sulfate/polyacrylamide gel electrophoresis. Monomeric and dimeric glycophorin A (NaIO4/Schiff‐2 and NaIO4/Schiff‐1 positive bands) and ‘band 4.5’ were identified as two major classes of methyl‐acceptor polypeptides for protein methylase II. In rabbit erythrocyte membrane where glycophorin A is absent, ‘band 4.5’ was the only major methyl‐acceptor protein component. Extracted and purified glycophorin A from human erythrocytes was also found to be an excellent substrate for protein methylase II with a Km of 35.7 μM. The role of erythrocyte membrane protein methylation is discussed with regard to membrane function.