15-Ch 6 chymotrypsin CHEM 481

What does Chymotrypsin specifically cleave in proteins?

Chymotrypsin cleaves peptide bonds on the C-terminal side of bulky aromatic or hydrophobic residues like tyrosine, phenylalanine, and tryptophan.

What is the function of the catalytic triad in chymotrypsin?

The catalytic triad (Ser195, His57, Asp102) activates serine, forming a nucleophile that attacks the carbonyl carbon of the substrate's peptide bond.

What role does the hydrophobic pocket play in chymotrypsin's mechanism?

The hydrophobic pocket provides substrate specificity by binding and positioning the aromatic side chain of the substrate.

How does the oxyanion hole contribute to enzyme catalysis in chymotrypsin?

The oxyanion hole stabilizes the negative charge on the oxygen atom of the tetrahedral intermediate during the reaction.

What happens when a suicide inhibitor modifies Ser195 in chymotrypsin?

The modification irreversibly inactivates chymotrypsin, preventing it from catalyzing further reactions.

What is the general function of an enzyme's active site?

The active site binds the substrate and catalyzes the chemical reaction, often using a combination of binding specificity and catalytic residues.

What is the significance of Ser195 in chymotrypsin?

Ser195 is unusually reactive for a serine residue because it is part of the catalytic triad and is activated by His57 and Asp102 to act as a nucleophile.

How does chymotrypsin lower the activation energy of amide bond hydrolysis?

Chymotrypsin stabilizes the transition state through interactions like the oxyanion hole and promotes substrate binding and positioning.

What does the term "substrate specificity" refer to in the context of chymotrypsin?

It refers to chymotrypsin’s preference for cleaving bonds next to aromatic or bulky hydrophobic residues, facilitated by its hydrophobic pocket.

Why can't chymotrypsin efficiently cleave bonds N-terminal to proline residues?

Proline’s unique ring structure prevents the formation of the required transition state for cleavage.

What is the purpose of the catalytic triad's charge relay system?

The charge relay system helps to deprotonate Ser195, making it a strong nucleophile that attacks the peptide bond carbonyl.

What does chymotrypsin use to stabilize the negative charge on the tetrahedral intermediate?

The enzyme uses the oxyanion hole, a region of the active site with partial positive charges that stabilize the negatively charged intermediate.

What are the two main kinetic steps in chymotrypsin’s catalysis?

The two main steps are the formation of the acyl-enzyme intermediate and the subsequent hydrolysis of this intermediate to release the second product.

How does enzyme catalysis differ from non-catalyzed reactions in terms of activation energy?

Enzyme catalysis significantly lowers the activation energy by stabilizing transition states and bringing substrates together in the correct orientation.

What role does His57 play in the catalytic mechanism of chymotrypsin?