FIII: Lecture Slides 58 - 68 Flashcards
What are inactivators?
Act on an enzyme irreversibly
What does inactivation result from?
Inactivation results from a covalent chemical reaction between the inactivator and the enzyme
Why is inactivation irreversible?
Due to the reaction destroying catalytic activity and the enzyme being used up.
What is the simple stoichiometric equation between the inactivator and the enzyme?
2 umol inactivator and 3 umol enzyme = 1 umol of active enzyme left
What are inactivators considered to be?
Extremely toxic (Example: nerve gases have the ability to inactivate acteylcholinesterase which then interferes with nerve impulses)
What are inhibitors?
Bind to enzymes irreversibly
What can an inhibitor do?
Decrease enzyme activity without destroying the catalytic function of enzyme molecule
What happens when the inhibitor concentration is removed?
The enzyme activity is restored
What type of reaction is inhabitation?
Binding equilibrium, as it can be reversed.
Competitive Inhibition
Where the inhibitor binds to the active site on the enzyme, where the substrate would bind (competing with substrate for active site)
Non-competitive Inhibition
Inhibition affects the catalytic rate, the inhibitor binds at an allosteric site separate from the active substrate binding site
What are inhibitors main job?
To regulate enzyme activity in a cell.
What is an example of two drugs that are inhibitors?
Aspirin and Advil:
Both drugs inhibit the cyclooxyrgenase enzyme that make prostaglandins: affect inflammatory response.
When can competitive inhibitors bind?
When the enzyme E is unoccupied (not with a substrate)
What is the inhibitor binding constant?
Ki
What does Ki equal?
[E][I]/[EI]
What is the reaction of an enzyme plus an inhibitor?
E + I —-> (rev) EI
Represented by Ki
What does the formation of the EI complex mean?
The formation means that there is less enzyme available to bind substrate
What can high [S] do?
Outcompete the competitive inhibitor
Why might the substrate and inhibitor have resemblance?
Because they share the same binding site, they may resemble each other in terms of chemical structure.
What happens when you graph enzyme behaviour in presence of competitive inhibitor vs. substrate when you keep [I] constant
The Km of the inhibitor is increased.
What is the equation for Km of Inhibitor?
Km’ = Km(1 + [I]/Ki)
What is Ki?
A characteristic constant for each inhibitor
What is the inhibition factor?
1 + [I]/Ki