the aim of this investigation was to find a nucleophile that would displace a methyl group from the sulfonium cation of [ s- [ 13c ] methylmethionine-192 ] -alpha-chymotrypsin without disrupting the five disulfide bridges of the protein , thereby producing [ [ epsilon-13c ] methionine-192 ] -alpha-chymotrypsin , an isotopically enriched version of the native enzyme desirable for 13c nmr studies .
C0042889
methylmethionine
C0025646
methionine