Chimotrypsin

Chymotrypsin – a class of hydrolytic enzymes that break down food proteins into peptides in the intestine. It is well soluble in water and in a solution of table salt. The pancreas synthesizes inactive chymotrypsinogens A and B (cyclic peptides), from which several chymotrypsins α, δ, π are formed in the duodenum. Activation occurs by acting on trypsin and by autolysis. During autolysis, initially inactive chymotrypsin is formed, later – other various chymotrypsins, which differ in enzymatic activity, physical, and chemical properties. The amino acid sequence of chymotrypsinogen A is similar to that of trypsin. The molecular mass is about 24,000, composed of a single polypeptide chain containing 246 amino acids. When catalyzed by trypsin, a peptide bond in the chymotrypsinogen A molecule is cleaved, located between arginine and isoleucine (initial cleavage between the 15th and 16th amino acids). π-chymotrypsin is formed, which has the highest enzymatic activity. The remaining segment is α-chymotrypsin. By cleaving the dipeptide Ser-Arg-, δ-chymotrypsin is formed. Two dipeptides are cleaved as if from chymotrypsinogen at two sites. Three polypeptide chain fragments formed from chymotrypsin genes remain connected due to supporting disulfide bonds. Chymotrypsin, like trypsin, is most active in an alkaline environment (pH – 7.2-7.8); it has serine in the active center, therefore, like trypsin, it is a serine protease. Chymotrypsin has a broader substrate specificity than trypsin. It hydrolyzes not only peptides but also esters, amides, and other acyl derivatives. Most actively, it hydrolyzes peptide bonds involving aromatic amino acids (phenylalanine, tyrosine, tryptophan). When trypsin and chymotrypsin cleave polypeptides from the stomach into the duodenum, short peptides and few free amino acids are formed.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė