4.3 Enzyme inhibitors Flashcards
What is an inhibitor?
molecules that prevent enzymes from carrying out their normal function of catalysis
–> two types of enzyme inhibition: competitive vs non-competitive
Competitive inhibition
A molecule/ part of molecule that has a similar shape to the substrate of an enzyme can fit into active site of enzyme
–> blocking the substrate from entering active site and preventing the enzyme from catalysing the reaction
–> Enzyme cannot carry out its function (inhibited)
Competitive inhibitors
Substrate and inhibitor molecules present will compete with each other to bind to the active site of the enzyme
–> reduces no of substrate molecules binding to active sites in a given time (slows down rate of reaction)
–> thus name (actively competing to bind to active site)
Most only bind temporarily to active site (reversible)
Effect of competitive inhibitors on rate of reaction
- Reduces rate of reaction for given conc of substrate
- no change to V max
However, if substrate conc is increased enough, much more substrate than inhibitor, allowing Vmax to be reached
Examples of competitive inhibition
statins are competitive inhibitors of an enzyme used to synthesis cholesterol
–< helps reduce blood cholesterol conc.
Aspirin irreversibly inhibits active site of COX enzymes
–> prevents synthesis of prostaglandins and thromboxane (chemicals that produce pain and fever)
Non-competitive inhibition
Inhibitor binds to enzyme at a location other than active site (allosteric site), causing a change in the tertiary structure of the enzyme.
–> changes active site so no longer a complementary shape to substrate
–> substrate can no longer bind to enzyme= enzyme cannot carry out function
Non-competitive inhibitor
- does not actively compete with substrate for active site
Effect of non-competitive inhibitors on rate of reaction
Increasing conc of enzyme/substrate will not overcome effect of inhibitor
–> Increased conc of inhibitor= lower rate of reaction= lower Vmax
Examples of non-competitive inhibitors
binding can be reversible/ non-reversible
–> irreversible cannot be removed: often toxic
e.g Organophosphates used insecticides and herbicides irreversibly inhibit enzyme acetyl cholinesterase (used for nerve impulse transmission).
–> can lead to muscle cramps, paralysis & even death
Proton pump inhibitors can irreversibly block an enzyme system for secreting H+ ions into stomach
–> effective in reducing production of excess acid which could lead to stomach ulcers
End product inhibition
The product of a reaction will act as an inhibitor to the enzyme that produces it (negative feedback mechanism to ensure excess is not made
How does respiration use end product inhibition
Respiration= metabolic pathway in producing ATP. Glucose is broken down in multiple steps:
1. addition of two phosphate gorups to glucose ( second phosphate group is catalysed by enzyme phosphofructokinase PFK(inhibited by ATP)
Negative feed back when ATP levels are too high?
High ATP= more ATP binds to allosteric site on PFK
–> prevents addition of second phosphate group to glucose
–> glucose is not broken down and ATP is not produced at same rate
Negative feed back when ATP levels are too low?
Low ATP= less binding to PFK
–> enzyme can catalyse addition of second phosphate group to glucose
–> respiration resumes= production of more ATP
