Chymotrypsin
I.U.B.: 3.4.21.1
Chymotrypsin preferentially catalyzes the hydrolysis of peptide bonds involving L-isomers of tyrosine, phenylalanine, and tryptophan. It also readily acts upon amides and esters of susceptible amino acids.
Characteristics of Chymotrypsin from Bovine Pancreas:
Forms: A pancreas extract contains equal amounts of two forms of the zymogen: Chymotrypsinogen A, with a molecular weight of 25,000 and and isoelectric point of 9.1, and Chymotrypsinogen B (E.C.3.4.4.6), with an isoelectric point of 5.2. Together, the zymogens represent 32% of the protein content of pancreatic extracts. Dependent upon the conditions, chymotrypsinogen A may be activated to α-, π-, δ-, β-, or γ-chymotrypsin. Desnuelle (1960) has provided a review of the activation and properties of chymotrypsin. The covalent strucuture of chymotrypsinogen A is given by Meloun et al. (1966).
Extinction coefficient: = 20.4.
Specificity: In addition to bonds involving aromatic amino acids, chymotrypsin catalyzes at a high rate the hydrolysis of bonds of leucyl, methionyl, asparaginyl, and glutamyl residues. A recent study has been made by Berezin and Martinek (1970) and Baumann et al. (1970).
Inhibitors: The enzyme is inhibited by heavy metals, the natural trypsin inhibitors to various degrees (Birk 1961), an inhibitor from potato (Ryan and Balls 1962), and organophosphorus compounds. Gel filtration of chymotrypsin removes autolysis products and other contaminants (Yapel et al. 1966). The specificity of α-chloroketone as α-chymotrypsin inhibitor has been studied by Kumar and Hein (1970). Erlanger et al. (1970) report phenothiazine-N-carbonyl chloride to be specific for chymotrypsin inhibition.
Stability: The enzyme is stable for days in solution at pH 3.0 and for years as a dry powder when stored refrigerated.