L14. Enzymes as Drug Targets Flashcards
What happens if a strongly bound substrate gives a product that also binds strongly to the active site?
Enzyme becomes clogged up and is unable to accept any more substrate.
If a medicinal chemist knows the position and nature of different binding region with an active site, is it possible to design molecules that will fit that active site, binding strongly, and act as inhibitors?
Yes
What is competitive inhibition?
An enzyme regulation method where a substrate can’t bind when a regulatory molecule, having a similar chemical composition to the substrate, binds to that enzyme’s active site. This blocks enzyme activity.
Define a reversible inhibitor.
It is a type of competitive inhibitor where the drug is competing with the natural substrate for the active site and is usually Similar in structure to substrate, product or cofactor.
It Binds reversibly to the active site more strongly having additional functional groups to form extra binding interactions to regions that are not occupied by the substrate and Undergoes no reaction.
True of False?
Inhibition depends on the strength of inhibitor binding, inhibitor concentration and the time of binding.
True.
Stronger binding, higher concentration, the longer present in the active site = greater inhibition
In terms of reversible inhibitors, if the concentration of substrate increases what will happen?
The substrate can compete more effectively with the drug, and so inhibition by the drug will be less effective.
Define irreversible inhibitors.
The inhibitor binds irreversibly to the active site by forming covalent bond and the substrate is permanently blocked from the active site.
likely to be similar in structure to the substrate.
Increasing substrate concentration does not reverse inhibition.
True or False?
Reversibile inhibitors have toxic side effects.
False. Its irreversible inhibitors.
What are the possible toxic side effects of irreversible inhibitors?
Reactive functional groups might react with other proteins, so it is generally better to inhibit with a reversible inhibitor.
Build-up of a particular substrate: Increasing the concentration of substrate will not reverse inhibition as the inhibitors cannot be displaced from the active site.
True or False?
Irreversible inhibitors are not competitive inhibitors.
True.
This is because they can’t be removed due to the permenant covalent bonds they form to the enzyme’s active site.
Inhibition of lipase will result in _______.
less fat synthesis
What is Orlistat?
Orlistat is an anti-obesity drug that inhibits lipase, blocking it from digesting fats in the intestine.
This results in less Fatty acids and glycerol absorption and Leads to reduced biosynthesis of fat in the body.
How does lipase aid biosynthesis of fatty acids and glceryol?
It binds between the fatty acid and glycerol backbone of lipid molecules. The digestion products are then absorbed and act as the building blocks for fat biosynthesis in the body.
Define allosteric activitation.
Active site becomes available to the substrates when a regulartory molecule binds to a different site on the enzyme.
Positive allosteric modulation (also known as allosteric activation) occurs when the binding of one ligand enhances the attraction between substrate molecules and other binding sites.
Define allosteric deactivation.
Negative allosteric modulation (also known as allosteric inhibition) occurs when the binding of one ligand decreases the affinity for substrate at other active sites.
The active site is distorted and is not recognized by the substrate.
For example, when 2,3-BPG binds to an allosteric site on hemoglobin, the affinity for oxygen of all subunits decreases.
How do Inhibitors Act at Allosteric Binding Sites?
The Inhibitor binds reversibly to the allosteric binding site via Intermolecular bonds.
The Induced fit alters the shape of the enzyme distorting the Active site and making it unrecognizable to the substrate
• Inhibitor is not similar in structure to the substrate
True or False?
Increasing substrate concentration does reverse inhibition of inhibitors bound to allosteric sites.
False.
• Increasing substrate concentration does not reverse inhibition
Explain the renin–angiotensin system. What is it an example of?
Renin, a Protease, hydrolyzes the peptide bond between Leucine and Valine in the protein angiotensinogen, removing Valine and Isoleucine which forms angiotensin I, a 10 amino acid peptide.
Angiotensin Coverting Enzyme (ACE) then removes the 2 C-terminal residues of Histidine and Leucine, forming Angiotensin II. Angiotensin II then Constricts blood vessels causing Retention of fluid in the kidneys, which in turn increases blood pressure.
How is Renin inhbited?
Transition state inhibition via an aspartic protease in an Acid-base mechanism involving coordination of a water molecule between the two Aspartic Acid amino acids.
- One Asp activates the water by abstracting a proton, enabling the water to attack the carbonyl carbon of the substrate scissile bond.
- This forms a tetrahedral intermediate that is then rearranged.
- Rearrangement of this intermediate leads to protonation of the scissile amide.
Explain the Reaction catalyzed by bacterial β-lactamase enzymes.
Serine reacts with Penicilin to open penicilin’s ring and form the nucleophile that is then reacted with β-lactamase and H+ to form an intermediate where Serine is covalently linked via an ester group to the ring-opened penicillin.
β-lactamase and water react with the intermediate to hydrolyze the ester group and release the inactivated penicillin and free up the active site, such that the catalytic process can be repeated.
