Lecture 12: Enzyme kinetics, inhibition and regulation II

Question 1

What is Vo or Vi?

Answer 1

Is the initial rate / velocity (at time zero) at a particular substrate concentration

Question 2

What are isoenzymes / isozymes?

Answer 2

• are different forms of a multi unit enzymes
• they differ in physical properties, kinetic properties and antigenic properties
• BUT they catalyse the SAME reaction

Question 3

What are zymogens?

How are they activated?

How does proteolytic cleavage regulate enzymes?

Answer 3

Zymogens are inactive forms of enzymes
Zymogens are activated by the cleavage of proteases to the zymogen polypeptide which removes a peptide/peptides to activate to the enzyme
- proteolytic cleavage activates zymogens

Question 4

How are enzymes regulated?

Answer 4

1. Allosteric effects
2. Covalent modification
3. Proteolytic cleavage

Question 5

How does allosteric effects regulate enzymes?

Answer 5

Activity can be regulated by binding of molecules away from the active site, which can inhibit or activate the enzyme
- These regulatory effects are achieved by conformation change in the protein when the effector molecule binds

Question 6

How does covalent modification regulate enzymes?

Answer 6

Is is the addition of molecule / group which changes its activity.

• are mostly reversible
• Phosphorylation/dephosphorylation involving sides chains of Ser, Thr or Tyr (R-OH)
• Enzymes involved are protein kinases and phosphates