RADIOACTIVE METHIONINE INCORPORATION INTO PEPTIDE CHAINS BY ENZYMATIC MODIFICATION

Enzymatic peptide modification was carried out using L-methionine-S-methyl-14C methyl ester hydrochloride and L-3H methionine ethyl ester hydrochloride in the reaction mixture. The experimental results revealed that part of the L-methionine-S-methyl-14 C methyl ester was bound as methionine to enzymatic hydrolysates of casein and serum albumin in the presence of α-chymotrypsin, interestingly in the highest molecular weight fraction of the product protein. A maximum curve was found to describe the relation between α -chymotrypsin-induced incorporation of methionine and the ratio of L-3H methionine ethyl ester to protein hydrolysate. The covalent nature of amino acid incorporation was supported by SDS polyacrylamide gel electrophoresis in the presence of urea. The isoelectric focusing patterns of the products indicate that transpeptidation plays an essential role in the EPM reaction. These experimental findings suggest that enzymatic peptide modification is a suitable method for the production of proteins of designed amino acid composition.