PEPTIDES CONTAINING THE FUNCTIONAL TYROSYL RESIDUES OF THE ACTIVE CENTER OF BOVINE PANCREATIC CARBOXYPEPTIDASE A

Abstract

The active region of bovine pancreatic carboxypeptidase A has been reported to contain functional tyrosyl residues. By iodinating two portions of the enzyme, one with I131-labeled iodine in the presence of the inhibitor, [beta]-phenylpropionate, and the other with I125-labeled iodine in the absence of the inhibitor and then analyzing the ratio of I125/I131 for the iodinated peptides isolated from a peptic digest of a mixture of the two preparations, it is shown here that the extents of iodination of more than one of the tyrosine residues of the enzyme are changed in the presence of the inhibitor relative to their extents without the inhibitor. Such tyrosine residues would appear to be those associated with the active site of the enzyme. There remains the possibility that conformational changes, if associated with binding of inhibitor, could alter the iodination rate of tyrosine residues elsewhere on the enzyme molecule and these are the ones isolated here.