Mechanism of Chymotrypsin ( protein hydrolysis ):
- The enzyme-substrate complex is formed by the formation of hydrogen bonds between the carbonyl group of the potential peptide bond and the amide hydrogen of Ser-196 and Gly-193.
- After the formation of the enzyme-substrate complex, the pKa of His-57 is increased, which activates the imidazole ring so that it can receive a proton from the hydroxyl of Ser-195. (General base catalysis)
- As a result, His-57 absorbs protons from the serine and makes the serine more nucleophilic.
- The nucleophilic serine attacks the carboxyl group of the substrate / protein and forms an oxynion intermediate.
- Asp-102 polarizes His-57 and stabilizes it through hydrogen bonds.
- The protons adopted by His are transferred to the amide nitrogen of the substrate / protein to form protonated amines.
- Then the protonated amine breaks down the amine part of the protein by breaking the CN bond.
- The subsequent arrival of H2O occurs. The OH ions of H2O attack the carbonyl carbon. And the H + ion of the water molecule is accepted by His.
- Ser-O-carbonyl breaks the bond with carbon and returns the proton from His-57, leaving the C-terminal portion of the substrate, and chymotrypsin returns to its former state to break up another new protein molecule.
How Chymotrypsin is activated:
Several proteolytic enzymes are involved in protein digestion that occur in the duodenum. Of all pancreatic zymogens. Trypsin acts as a general activating enzyme. The combined activation of these proteases is achieved by the action of trypsin. An enzyme called enteropeptides secreted from the duodenum converts trypsin from its inactive form trypsinogen to the active form trypsin. Enteropeptides hydrolyze a unique lysine-isolyucine peptide bond to produce active trypsin. Trypsin cleaves the peptide binding to Arg-15 and Isoleucine-16, converting chymotrypsinogen to fully activated chymotrypsin. This active chymotrypsin is called π chymotrypsin. This π chymotrypsin later works on another π chymotrypsin molecule. As a result alpha-chymotrypsin is produced. Two dipeptides are removed from π chymotrypsin to produce alpha chymotrypsin which is a more stable form of the enzyme chymotrypsin.
Chymotrypsin (its structure and properties) :
Chymotrypsin is a digestive enzyme that is produced in pancreatic acinar cells and is stored inside membrane-bound particles. Chymotrypsin contains a single polypeptide chain consisting of residues of 245 amino acids, virtually free from enzymatic activity. Chymotrypsin contains both alpha-helical and beta-sheath domains. The two domains are folded into an elliptical structure. Asp 102, His-57, Ser-195 form an enzymatic triad. The side chain of Ser 195 is attached to the imidazole ring of His -57 by hydrogen bonding. The NH group in the imidazole ring is in turn bound to the carboxylate group of Asp-102.
- Molecular weight of chymotrypsin is 25.6 kDa
- Optimal pH 7.8-8.0
- Optimal temperature 40-50 degree celcius
- Isoelectric points 8.52 (chymotrypsinogen) and 8.33 (chymotrypsin)
- Extinction coefficient 51840/cmM
The enzyme Chymotrypsin catalyzes two important reactions:
- Hydrolysis of peptide bonds
- Hydrolysis of ester bonds
Functions of Chymotrypsin :
- Helps in digestion
- Treats inflammation
- Reducing swelling
- Excretion of mucus
- Killing digestive worms and parasites
- Acting as a wound cleaner
- Used to treat ulcers, acne
- Helps in the treatment of asthma, bronchitis, lung diseases, sinus infections
- Treatment of fractures and burns
- Cure pelvic inflammatory disease