Lecture 10 Flashcards
What is the lower limit for catalytic perfection?
10^8 s^-1 M^-1
What is an enzyme inhibitor?
A compound that binds to an enzyme and reduces its activity
Why are enzyme inhibitors important?
Natural inhibitors regulate metabolism; many drugs, poisons and toxins are inhibitors; they can be used to study enzyme mechanisms and metabolic pathways
What are the two classes of inhibitor?
Irreversible and reversible inhibitors
What is an irreversible inhibitor?
An inhibitor that binds covalently to the enzyme in order to permanently inactivate it
What does an irreversible inhibitor react with?
Covalently with a specific amino acid side chain, usually in the active site
What is a reversible inhibitor?
Inhibitor that is non-covalently bound to the enzyme and can be subsequently released, leaving the enzyme in its original condition
What does a reversible inhibitor change?
The kinetic parameters of the enzyme
What are the two forms of reversible inhibitors?
Competitive and non-competitive
What is a competitive inhibitor?
A inhibitor that competes directly with the substrate, for the active site
What is the change in the kinetic parameters of a competitive reversible inhibitor?
An increased Km, more substrate needed in order to reach V = Vm/2
What is a biological example of a competitive reversible inhibitor?
Transition state analogues e.g. Lipitor competing with the inhibitor Anastrozole. This is a treatment for some forms of breast cancer
What is a non-competitive inhibitor?
An inhibitor that binds at a different site than the substrate, therefore the enzyme can bind to substrate, inhibitor or both
What does a non-competitive reversible inhibitor do to the enzyme?
Slows does the ability of the substrate to react
What is the change in the kinetic parameters of a non-competitive reversible inhibitor?
Vmax is decreased and therefore V is too.
