Final Answer:
The three key amino acid residues present in the active site of chymotrypsin are histidine (His-57), aspartic acid (Asp-102), and serine (Ser-195).
Step-by-step explanation:
Chymotrypsin, a digestive enzyme, belongs to the serine protease family and contains an active site formed by three crucial amino acid residues: histidine (His-57), aspartic acid (Asp-102), and serine (Ser-195). The mechanism of chymotrypsin involves a catalytic triad where these residues collaborate in a series of reactions. Initially, His-57 acts as a general base and extracts a proton from Ser-195, which activates Ser-195 and creates a nucleophilic alkoxide ion. This highly reactive intermediate attacks the peptide substrate, leading to the formation of an acyl-enzyme intermediate.
Following this, Asp-102, through its negative charge, stabilizes the intermediate formed by Ser-195. This stabilization facilitates the cleavage of the peptide bond within the substrate molecule. The resulting products are released from the enzyme, regenerating the initial state of the enzyme to continue catalyzing further reactions. The synergy among these three residues is essential for the catalytic activity of chymotrypsin, enabling the enzyme to efficiently break down proteins into smaller peptide fragments during digestion.
Understanding the roles played by His-57, Asp-102, and Ser-195 in the catalytic mechanism of chymotrypsin is crucial in comprehending enzymatic processes. Their coordinated actions highlight the significance of specific amino acid residues in enzyme function, showcasing the intricate nature of biochemical reactions catalyzed by enzymes like chymotrypsin in biological systems.