Isolation and partial characterization of a covalent intermediate between α-chymotrypsin and o-hydroxy-α-toluenesulfonic acid sultone

Abstract Reaction of α-chymotrypsin with o -[ 35 S]hydroxy-α-toluenesulfonic acid sultone ( I ) at pH 7 produces an intermediate which substantially decomposes over a period of 24 hr at pH 3 as determined by gel chromatography. Isolation of the intermediate at pH 3 followed by denaturation in urea, reduction of disulfide bonds, and SDS-urea gel electrophoresis resulted in separation of the three peptides which compose the enzyme. Radioactivity ( 35 S) was associated with the peptide which contains serine 195 and not with the peptide containing histidine 57. These results indicate that a covalent linkage is established between sultone I and α-chymotrypsin, presumably at serine 195.