Question

Please describe how chymotrypsin, the model serine protease enzyme, uniquely uses a catalytic triad to catalyze the hydrolysis of a protein chain.

a. Types of amino acids at the active site and why that combination is important in this example.

b. Which of the three mechanisms for enzyme catalysis are demonstrated by this enzyme (strain, add charges, orient correctly)?

c. Summary of the mechanism of the catalytic process. No need to mention specific orbitals, just in general what does each amino acid do to facilitate the cleavage of the peptide bond?

d. Does this enzyme contribute to anabolism or catabolism? Relate this to condensation or hydrolysis

e. What would happen if we changed aspartic acid to isoleucine? Explain why

Answer 1

Question

a. Chymotrysin is an enzyme involved in the breaking of peptide bonds present in the protein. The three amino acids which are present in the active site of the enzyme are involved in the breaking of peptide bonds and are known as catalytic-triad. These amino-acid are aspartic acid at 102 position, histidine at 57 position and serine at 105 position. These 3 amino acid break the peptide bond by forming oxyanion hole.

b. The mechanism for the hydrolysis involved in the chymotrysin is by adding charges.

c. The aspartic -acid in this catalytic triads polarizes the base (histidine amino acid)which further activate base that activates the nucleophile which is serine. Thus, this catalytic triads forms a catalytic triads that break the protein into smaller peptides.

Figure: Role of each amino acid

d. This enzyme relate to the catabolism because this enzyme break the protein into small peptides.

e. The function of chymotrysin will changed if aspartic acid mutated to isoleucine because aspartic acid is a acidic amino acid and isoleucine is a basic amino acid.