Chymotrypsin

Question 1

Which side chains form the catalytic triad?

Answer 1

His57, Asp102, and Ser195

Question 2

What occurs in step 1?

Answer 2

• Substrate binds

- Side chain of the residue adjacent to the peptide bond to be cleaved enters the hydrophobic pocket

Question 3

What type of reaction occurs in step 2?

Answer 3

General base

Question 4

What occurs in step 2?

Answer 4

Electrons flow from catalytic triad to substrate

Question 5

What is formed after step 2?

Answer 5

First tetrahedral intermediate

Question 6

What causes the pKa to change in step 2 and what does it change to?

Answer 6

• Substrate binding compresses the bond between Asp102 and His57
• pKa of His57 becomes above 12

Question 7

What stabilizes the oxyanion hole?

Answer 7

H-bonding to groups in the protein

Question 8

What type of bond forms in the first tetrahedral intermediate?

Answer 8

Covalent bond between enzyme and substrate

Question 9

What occurs in step 3?

Answer 9

Electrons flow from substrate to general acid catalytic triad

Question 10

What stabilized the C-terminal peptide in step 4?

Answer 10

The donated proton

Question 11

When is the first product released?

Answer 11

In step 4

Question 12

What occurs in step 4?

Answer 12

• C-N bond is cleaved and the C-terminal peptide is released

- Product 1 is released and remaining substrate inside the enzyme is called the acyl-enzyme intermediate

Question 13

What occurs in step 5?

Answer 13

• A water molecule is activated by His57, creating a hydroxyl group
• Hydroxyl group that attacks the carbonyl carbon of the ES intermediate

Question 14

How is the N-terminus released?

Answer 14

Hydrolysis

Question 15

What occurs in step 6?

Answer 15

His57 acts as a general acid and protonates Ser195, causing the collapse of the 2nd tetrahedral intermediate

Question 16

What occurs in step 7?

Answer 16

• N-terminal product is released

- Catalytic triad is ready to receive another substrate