Lecture 18 Mechanism of Enzyme Action

Mechanism of Catalysis

a. By proximity
b. Covalent catalysis
c. General acid base catalysis
d. Metal ion catalysis
e .Low barrier hydrogen bonds

Proximity

enzyme brings substrate

Near attack complexes

Reacting atoms 3.2A and approach angle of +-15 degrees of the bonding angle in the transition state.
Alcohol dehydrogenase

Protein motions are essential to enzyme catalysis

a. Proteins are constantly moving-bonds are vibrating side chains are rotating
b. Active site conformation can change

Active site conformation can change

i. Assist substrate binding
ii. Bring catalytic groups into position
iii. Induce formation of NAC (near attack complexes)
iv. Assist in bond making and bond breaking
iiv. Facilitate conversion of substrate to product

Covalent Catalysis

a. Active sites form from temporary covalent bond with the substrate★
b. Occurs due to nucleophilic attack by amino acid side chains★
c. Can involve prosthetic groups
d. Facilitate electron transfer★
Most have unknown mechanisms

Double Displacement

a .two substrates binding and reacting separately in a ping pong manner★
b. E' is a covalently modified enzyme intermediate ★