Intermolecular Reaction during Photolysis of Diazoacetyl α-Chymotrypsin

Photolysis of 14C-labeled diazoacetyl α-chymotrypsin incorporates radiocarbon into the protein; O-carboxymethyl-tyrosine had previously been found in the hydrolysate of the photolysis product. Now this tyrosine residue has been identified as number 146 in the amino acid sequence by partial degradation of the protein, followed by enzymic release of the labeled residue. It has been further identified by showing that photolysis of diazoacetyl δ-chymotrypsin (where the carboxyl end of tyrosine 146 is not free) yields little if any carboxymethyltyrosine. These and other data suggest that the reaction with tyrosine 146 occurs in the chymotrypsin dimer, between one subunit and its neighbor.