Selective methyl esterification of erythrocyte membrane proteins by protein methylase II

Abstract

Methyl esterification of [rat] erythrocyte membrane proteins was demonstrated by incubating the isolated membrane with purified protein methylase II (S-adenosyl-methionine:protein-carboxyl 0-methyltransferase, EC 2.1.1.24) and S-adenosyl-L-[methyl-14C]methionine. Methyl esterification of membrane-bound proteins occurred selectively to proteins corresponding to bands 3 (MW 97,000), 4 (MW 75,000) and 4.5 (MW 48,000) as identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Mild alkali treated depleted vesicles which lacked bands 1, 2, 5 and 6 had a higher methyl accepting capacity (500 pmol of methyl groups/mg of depleted vesicle proteins vs. 200 pmol of methyl groups/mg of intact membrane proteins). Alkali-extractable membrane components were not methylated.