The active site of an enzyme is a specific region on the enzyme where the substrate binds, and the catalytic reaction takes place. The interaction between the enzyme's active site and its substrate involves several non-covalent interactions, such as hydrogen bonding, electrostatic interactions, and hydrophobic interactions. These interactions help to stabilize the enzyme-substrate complex and facilitate the catalytic reaction.Chymotrypsin is a serine protease enzyme that catalyzes the hydrolysis of peptide bonds, specifically at the carboxyl side of aromatic or large hydrophobic amino acids like tryptophan, tyrosine, and phenylalanine. The catalytic mechanism of chymotrypsin involves three key amino acid residues in its active site, which are part of the catalytic triad: serine Ser , histidine His , and aspartate Asp .Here is a step-by-step description of the catalytic mechanism for the hydrolysis of a peptide bond by chymotrypsin:1. Substrate binding: The substrate binds to the active site of chymotrypsin, with the peptide bond to be cleaved positioned near the catalytic triad. The enzyme's specificity pocket accommodates the side chain of the target amino acid, ensuring proper positioning for catalysis.2. Nucleophilic attack: The histidine residue in the catalytic triad acts as a base, abstracting a proton from the serine residue's hydroxyl group. This process generates a highly reactive alkoxide ion on serine, which acts as a nucleophile and attacks the carbonyl carbon of the peptide bond.3. Tetrahedral intermediate formation: The nucleophilic attack results in the formation of a tetrahedral intermediate, with the carbonyl oxygen now bonded to the serine residue. This intermediate is stabilized by hydrogen bonding with the histidine and a nearby backbone amide nitrogen oxyanion hole .4. Cleavage of peptide bond: The histidine residue donates the previously abstracted proton to the nitrogen of the peptide bond, leading to the cleavage of the peptide bond and the release of the first product the N-terminal portion of the substrate .5. Water molecule entry: A water molecule enters the active site and is deprotonated by the histidine residue, generating a hydroxide ion.6. Nucleophilic attack by water: The hydroxide ion acts as a nucleophile and attacks the carbonyl carbon of the acyl-enzyme intermediate, forming a second tetrahedral intermediate.7. Release of the second product: The histidine residue donates a proton to the serine residue, leading to the collapse of the tetrahedral intermediate and the release of the second product the C-terminal portion of the substrate .8. Enzyme regeneration: The enzyme returns to its original state, with the catalytic triad ready for another round of catalysis.In summary, the active site of chymotrypsin interacts with its substrate through non-covalent interactions, and the catalytic mechanism for the hydrolysis of a peptide bond involves a catalytic triad consisting of serine, histidine, and aspartate residues.