Evidence is presented for specific enzymatic methylation of 21–23 kDa membrane proteins in intact neuroblastoma N1E 115 cells, which is increased in dimethylsulfoxide-induced differentiated cells. Methylation of these proteins has characteristics typical of enzymatic reactions in which base labile volatile methyl groups are incorporated into proteins, consistent with the formation of protein carboxyl methylesters. However, these methylesters of the 21–23 kDa proteins are relatively stable compared to other protein carboxyl methylesters. The 3-fold increase in methylated 21–23 kDa proteins in the differentiated cells suggest biological significance in differentiation of the cell membranes.
