Chymotrypsinogen is synthesized in the body in the pancreas. It is activated by

Question

Chymotrypsinogen is synthesized in the body in the pancreas. It is activated by trypsin, which cleaves out a dipeptide from chymotrypsinogen to make chymotrypsin. Why is chymotrypsin not synthesized directly in the pancreas? Removal of the dipeptide by trypsin would normally cleave the protein in half. Why does it not fall apart? How might this change allow for the protein to perform its intended function? Chymotrypsin tends to cleave amino acid chains at tyrosine, tryrptophan and phenylalanine. Explain this selective tendency of this enzyme.

Explanation / Answer

a)Several proteases are synthesized in the pancreas. But two major pancreatic proteases trypsin and chymotrypsin are synthesized and packaged into secretory vesicles as inactive proenzymes trypsinogen and chymotrypsinogen.

Chymotrypsin is dangerous enzyme to have in cells, and packaging of an inactive precursor is a way for the cells to safely handle these enzymes. The secretory vesicles also contain a chymotrypsin inhibitor which serves as an additional safeguard.

Once chymotrypsinogen is released into the lumen of the small intestine, it must be converted into its active forms in order to digest proteins.

b) Removal of di peptide by trypsin would normally cleave the protein into half. It does not due to presence of a positively charged residue in the S1 binding pocket.

c) Chymotrypsin is a digestive enzyme belonging to serine proteases. It uses an active serine residue to perform hydrolysis on the C-terminus of the aromatic amino acids of other proteins. Chymotrypsin is a protease enzyme that cleaves on the C-terminal phenylalanine, tryptophan, and tyrosine on peptide chains. It shows specificity for aromatic amino acids because of its hydrophobic pocket. It cleaves polypeptides, and its specificity allows it to act only on the carboxy-terminal of aromatic residues.

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