The catalytic activity of carboxypeptidase-degraded aldolase.

One approach to the general problem of the structure and function of enzymes involves proteolytic hydrolysis with examination of the structure, composition, and catalytic activity of the hydrolysis products. Fragments retaining partial enzyme activity have been obtained from trypsin and pepsin by autolysis (2, 3) and from trypsinogen by peptic digestion (4). Over half of the amino acid residues of papain may be removed by aminopeptidase without activity loss (5). Ribonuclease loses activity when a peptide of 20 residues is removed from the NH&erminal end, but regains activity when recombined with the peptide (6). Removal of COOH-terminal residues by carboxypeptidase has little effect on the activity of chymotrypsin (7), lysozyme (S), or ribonuclease (9, 10). In contrast, studies in this laboratory, preliminary to the investigations reported herein, (II), showed that treatment of muscle aldolase by crude trypsin or carboxypeptidase readily caused marked activity loss. The purpose of this paper is to present observations on the striking decrease in aldolase catalytic activity and concomitant change in specificity accompanying release of terminal tyrosine residues by carboxypeptidase digestion.