4.3 Enzyme Inhibitors Flashcards
Why do enzymes need to be inhibited
Controlling the activity of enzymes at crucial points in these multi step reaction pathways regulates the rate and quantity of product formation.
What activates enzymes? What inactivates enzymes?
Activated with cofactors. Inactivated with inhibitors
What is an inhibitor?
Molecule that prevents enzyme from varying out its normal function of catalysis (or slows it down)
Types of enzyme inhibition
Competitive and non competitive
Ways that competitive inhibition works
Molecule or part of a molecule that has a similar shape to the substrate of an enzyme can fit into the active site
This blocks substrate from entering active site, preventing enzyme from catalysing the reaction
Enzyme cannot carry out its function and is said to be inhibited.
Why are they called competitive inhibitors
Nonsubstrate molecule that binds to the active site is a type of inhibitor
Substrate and inhibitor molecules present in a solution will compete w each other to bind to active sites of the enzymes catalysing the reaction
Reduces number of substrate molecules binding to active sites in a given time and slows down rate of reaction
What does the degree of inhibition rely on?
Relative concentrations of substrate, inhibitor and enzyme
Competitive inhibitors effect in rates of reaction
Reduced rate of reaction for a given concentration of substrate but does not change the Vmax of the enzyme it inhibits.
If substrate concentration is raised enough then there’ll be enough substrate for the Vmax to still be reached
Examples of competitive inhibition
Statins - competitive inhibitor of enzyme used in synthesis of cholesterol. Regularly prescribed to help people reduce blood cholesterol concentration. High blood cholesterol levels can result in heart disease
Aspirin - irreversibly inhibits active site of COX enzymes preventing synthesis of prostaglandins and thromboxane (chemicals responsible for producing pain and fever)
How does non competitive inhibition work
Inhibitor binds to enzyme at a location other than the active site (allosteric site)
Binding if inhibitor causes tertiary structure of enzyme to change - active site changes shape
Active site is no longer having a complementary shape to the substrate so it is unable to bind to the enzyme
Enzyme cannot carry out its function - inhibited
Why are they called non competitive inhibitors
Does not compete with substrate for active site
Non competitive inhibition effect on rate of reaction
Increasing concentration of enzyme or substrate will not overcome effect of a non competitive inhibitor. Increasing concentration of inhibitor will decrease reaction as more active sites become unavailable
Examples of irreversible non competitive inhibitors
Organophosphates - insecticides and herbicides irreversibly inhibit enzyme acetyl cholinesterase. This enzyme is necessary for nerve impulse transmission. This can lead to muscle cramps, paralysis, and even death if accidentally ingested.
Proton pump inhibitors (PPIs) - treat long term indigestion. Irreversibly block an enzyme system responsible for secreting H ions into the stomach. Makes PPIs effective in reducing production of excess acid which if untreated could least to stomach ulcers
What is End product inhibition
Used for enzyme inhibition that occurs when product of reaction acts as an inhibitor to enzyme that produces it
Why end product inhibition is useful
Serves as a negative feedback control mechanism for the reaction.
Excess products are not made and resources are not wasted
