Week 10: Enzyme inhibition and reaction kinetics Flashcards
What is an enzyme inhibitor?
A substance that inhibits the catalytic action of the enzyme.
Give an example of an enzyme inhibitor.
For example, irreversible inhibitors, or catalytic poisons decrease the activity of the enzyme to zero.
This is the method of action of cyanide, and many nerve gases.
How do enzymes work?
An enzyme molecule is usually a large protein, considerably larger than the substrate molecule whose reaction is catalysed.
Embedded in the large enzyme protein are one or more active sites, to which the substrate can bind to form the complex.
An enzyme catalyses a single reaction, or substrates with similar structures.
Why do enzymes only affect a single reaction?
This is believed to be a steric property of the enzyme that results from the three dimensional shape of the enzyme allowing it to fit in a “lock and key” fashion with a corresponding substrate molecule.
What are the two types of enzyme inhibitors?
competitive
allosteric
How do competitive inhibitors work?
If another molecule has a shape similar enough to that of the substrate molecule, it may also bind to the active site, preventing the binding of a substrate molecule, thus o
inhibiting the reaction.
Because the inhibitor competes with the substrate molecule for the active site, it is called a competitive inhibitor.
How do allosteric inhibitors work?
If the enzyme molecule has other binding sites, distinct from the active site, the binding of which affects the activity of the enzyme of the active site.
These binding sites are called allosteric sites or regulatory sites, binding of which can regulate the catalytic activity of the protein.
The ligand that binds at the allosteric site is can an effector or modifier.
If it increases the activity of the enzyme, it is called and allosteric activator; if it decreases the activity, it is called an allosteric inhibitor.
Why does the allosteric effect arise?
It is presumed to arise because of a conformational change of the enzyme.
A change in the folding of the polypeptide chain, called an allosteric transition.
