Enzymes As Drug Targets Flashcards
Define: Vmax
The maximum rate at which an enzyme can carry out a reaction
Define: Km
The substrate concentration at which the enzymes will work at 1/2 of Vmax
What is plotted on a Lineweaver-Burke plot?
Reciprocals: 1/V and 1/[S]
What does the intercept on the y axis of a Lineweaver-Burke plot indicate?
1/Vmax
What does the intercept on the x axis of a Lineweaver-Burke plot indicate?
-(1/Km)
What is an issue with just plotting initial reaction rate vs substrate concentration to calculate Vmax and Km?
The eventual substrate concentration reached for the Vmax is actually quite difficult to reach - end up saturating the reaction
What does the gradient of a Lineweaver-Burke plot indicate?
= Km/Vmax
Define: Ki
A constant - describes how frequently an inhibitor will bind to the enzyme
Define: K’i
A constant - describes how frequently an inhibitor will bind to an ES complex
Define: Competitive inhibition
Where an inhibitor binds to an enzyme’s active site to prevent the substrate from binding. It is usually reversibly bound
What happens to the Vmax, Km and gradient of an L-B plot when a competitive inhibitor is introduced?
- The gradient becomes steeper
- Vmax stays the same (as long as enough substrate)
- Km is altered
Therefore less substrate is processed and a higher concentration of substrate is required to reach 1/2Vmax
What happens to the Vmax, Km and gradient of an L-B plot when a non-competitive inhibitor is introduced?
- The gradient becomes steeper
- Vmax is altered
- Km stays the same
This is because there is a smaller enzyme population = lower Vmax
Define: non-competitive inhibitor
Bind directly to the active site, are irreversibly bound
What is prevented when viral enzymes are targeted by drugs?
Prevents viral replication
What do bactericidal drugs target?
Enzymes produced by bacteria that are not found or are different in humans = specificity
What do DD transpeptidases do?
Carry out crosslinking of peptidoglycan wall subunits for bacteria (Also known as penicillin binding protein, PBP)
What type of drug targets DD transpeptidases?
Beta lactam antibiotics
How do beta lactam antibiotics kill bacteria cells?
- The antibiotics bind to and irreversibly inhibit DD transpeptidase (which cross-links the peptidoglycan wall units)
- Bacterium cannot split into 2 daughter cells with cell walls
- Therefore, a spheroplast is formed (no cell wall) and cell will burst
Name the enzyme that counteracts beta lactam antibiotics
Beta lactamases give the bacteria antibiotic resistance = enzymatic defence system
What does HIV protease do in a virus molecule?
Processes (cleaves) viral virion proteins required for the formation of the active virus
Name a drug that targets HIV protease
Atazanavir
What organ is ACE (angiotensin converting enzyme) responsible for regulating?
The kidney
What is the mechanism of action of ACE?
ACE acts as a protease, cleaving angiotensin I and converting it into angiotensin II = the active form of the peptide
Name the enzyme that converts angiotensinogen to angiotensin I
Renin
What enzymatic conversion process is renin responsible for?
Converting angiotensinogen to angiotensin I
Name the enzyme that Ramipril targets
ACE
Name the drug that targets ACE
Ramipril
What is Ramipril’s mechanism of action?
- Ramipril inhibits the proteolytic activity of ACE
- So the production of Angiotensin II is decreased
- This decreases fluid retention
- Resulting in lower blood pressure
What condition is Ramipril prescribed for?
High BP
What does COX stand for?
Cyclo-oxygenase
Define: cyclo-oxygenase
Enzymes which are responsible for the production of prostaglandins (important for inflammatory response)
What is the mechanism of action of Ibuprofen?
- Binds to the active site of COX enzymes
- Prevents the substrate (arachidonic acid) binding
- Inhibits the production of prostaglandins
- Inflammation and pain are reduced
How do kinases regulate the activity of proteins?
By altering their structure using the addition of a phosphate group
Define: allosteric modulation
When a substance indirectly influences (modulates) the effects of the agonist at a target protein (i.e. enzyme)
How does allosteric binding alter the function of an enzyme?
- The allosteric substrate alters the overall protein shape when it binds
- This can lead to altered substrate binding or active site function
How does ‘co-operative activity’ change the shape of a r/r vs [S] curve?
S-shaped curve, reaction starts off slow (initial r/r) and then accelerates according to the increase in [S]
Slow initial rate due to low affinity for ligand/substrate, as affinity increases so does rate of reaction
Define: co-operative activity/binding
Occurs in complexes made up of several molecules
- A ligand binds to one of the molecules
- The overall shape of the protein is altered
- The other active sites of the complex are altered so they are more likely to pick up the ligand
- Affinity increased
Give an example of co-operative binding
Haemoglobin: made up of multiple molecules of beta globin, when oxygen binds affinity for O2 increases
Name 3 ways that allosteric binding can change an enzyme to make a reaction more likely
- AS opening
- Formation of AS
- Enhancement of dimerisation (binding of 2 proteins/enzymes creates an AS)
^^ All due to allosteric binding of a ligand
Name 3 ways that allosteric binding can change an enzyme make a reaction less likely
- AS closing
- Active site distortion
- Inhibition of dimerisation (prevents, blocks)
^^ All due to allosteric binding of a ligand
