Final answer:
Chymotrypsin's reaction mechanism involves a nucleophilic attack on peptide bonds by a serine residue in its active site, forming an acyl-enzyme intermediate followed by hydrolysis. The entire process is facilitated by the catalytic triad of serine, histidine, and aspartate.
Step-by-step explanation:
The reaction mechanism for chymotrypsin involves a series of steps in which this enzyme catalyzes the cleavage of peptide bonds adjacent to aromatic amino acids like phenylalanine, tyrosine, and tryptophan. Initially, chymotrypsin is secreted as an inactive precursor called chymotrypsinogen, which is then activated by another enzyme, trypsin, into its active form.
Once activated, chymotrypsin utilizes a serine residue in its active site to initiate a nucleophilic attack on the peptide bond, leading to an acyl-enzyme intermediate that is then resolved by water, releasing the cleaved peptide and regenerating the free enzyme.
A key feature of this reaction is the role of the serine hydroxyl group, which acts as the nucleophile in an acyl substitution reaction. This nucleophilic attack is facilitated by a catalytic triad within the enzyme, composed of serine, histidine, and aspartate, which work together to create a charged environment optimal for the reaction.
After forming the acyl-enzyme intermediate, water is brought into the reaction by histidine to hydrolyze this intermediate, resulting in the cleaved peptide and returning the enzyme to its original state ready for another catalytic cycle.