upon repeating the experiment with [ s- [ 13c ] methylmethionine-192 ] -alpha chymotrypsin , we isolated in 40 % yield a protein which was identified as [ [ epsilon-13c ] methionine-192 ] -alpha-chymotrypsin by a combination of 13c nmr and chemical criteria .
C0042889
methylmethionine
C0025646
methionine