The two human chymotrypsinogens. Purification and characterization.

The two chymotrypsinogens present in human pancreatic juice have been purified and characterized. The zymogens are two immunologically and electrophoretically different proteins. Chymotrypsinogen A, the major chymotryptic component (90% of the total potential N-acetyl-L-tyrosine ethylester activity) is stable in acidic medium. By its molecular weight (approx. 24 000), specific activity (530) and amino acid composition, human chymotrypsinogen A resembles chymotrypsinogens A and B form bovine and porcine pancreas. Chymotrypsinogen B is a minor chymotryptic component (7% of the total potential N-acetyl-L-tyrosine ethylester activity) unstable in acidic medium with a molecular weight slightly higher (approx. 27 000) and a specific activity slightly lower (300) than chymotrypsinogen A. The last 3% of the total potential N-acetyl-L-tyrosine ethylester activity corresponds to a proelastase that we have partially characterized.