1. Enzyme Mechanisms: Serine Proteases
C483 Spring 2013

2. Questions
1. The substrate specificity of serine proteases is primarily due to
A) a specificity pocket in the protein.
B) the positions of specific side chains of serine, histidine, and aspartate.
C) distinct backbone conformations of the individual proteins.
D) A and B.
E) A, B and C.
2. The role of serine at the active site of serine proteases is to act as a(n) ________ catalyst, while the histidine residue serves as a(n) ________ catalyst.
A) strong; weak
B) weak; strong
C) acid-base; covalent
D) covalent; acid-base
E) anionic; ionic
3. Experiments on the bacterial serine protease subtilisin show that even when all three residues of the catalytic triad are mutated, the catalytic rate of the enzyme is still 3000 times the uncatalyzed reaction rate. Which mode of catalysis is likely responsible for this remaining catalytic activity?
A) Acid-base catalysis.
B) Covalent catalysis.
C) Induced fit.
D) Hydrophobic effects.
E) Transition-state stabilization.

3. Proteases Role in Digestion Zymogens Serine Proteases Homology
Chymotrypsin
Trypsin
Elastase
Homology

4. Selectivity of Serine Proteases

5. Mechanism of Serine Proteases: Catalytic Triad

6. Chemical Mechanism Substrate binding affects Histidine base strength
Covalent catalysis
Oxyanion hole
Covalent intermediate

7. Chemical Mechanism Read from bottom! General acid-base catalysis
Oxyanion hole
Return to initial state
Compare/contrast to Main Protease

8. Answers A D E