Lecture 16 - Enzyme Classes, Chymotrypsin

What are the seven major enzyme classes?

1. oxidoreductases

2. transferases

3. hydrolases

4. lyases

5. isomerases

6. ligases

7. translocases

Oxidoreductases

redox reaction to transfer e- between molecules

Transferases

transfer functional groups; catalyze bimolecular reactions

Hydrolases

cleave molecules by adding water

Lyases

double bonds; remove/add atoms or functional groups

Isomerases

move functional groups within a molecule; form isomers

Ligases

join two molecules together with ATP hydrolysis (glue)

Translocases

catalyze movement of ions/molecules across membranes

What is chymotrypsin?

enzyme helping to hydrolyze dietary proteins into small peptides for absorption by the small intestine

What is the substrate specificity of chymotrypsin?

cleaves preferentially on the C-terminus of bulky hydrophobic R groups (Phe, Met, Trp, Tyr, Ile)

What is the function of Asp 102 in chymotrypsin?

orients His 57 through H bonding and electrostatic interactions

What is the function of His 57 in chymotrypsin?

general acid-base catalyst, accepts an H from Ser 195 to generate an alkoxide ion (nucleophile). Initially acts as a general base (accepts H+)

What is the function of Ser 195 in chymotrypsin?

its Oxygen side chain acts as a nucleophile

What is the function of the oxyanion hole?

stabilizes the tetrahedral intermediate through H bonds

What kind of bimolecular reaction does chymotrypsin exhibit?

double displacement (ping-pong)

What class of enzyme is chymotrypsin?

hydrolase