Drug Targets: Enzymes Flashcards
Define enzyme
Substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process
Binding interactions for enzyme catalysis should be?
Strong enough to hold substrate long enough for reaction to occur
Weak enough to allow product to leave
Michaelis-menten equation relates reaction rate to?
Substrate concentration
What is vmax?
Enzyme maximum reaction rate
Km ( Michaelis constant) is
Measure of affinity of the substrate for the enzyme
How to measure km?
Half of Vmax
Lineweaver burk plot, function?
Turn michaelis-menten equation into a straight line plot
Benefit of lineweaver burk plot
Allows you to estimate vmax and km more accurately
3 types of reversible inhibition
Competitive
Non-competitive
Uncompetitive
Inhibitor competes with substrate for active site
Competitive inhibitor
How to overcome competitive inhibition?
Increase levels of substrate
Inhibitor binds to a different site (allosteric site)
Non-competitive
Can you overcome non-competivite inhibition by increasing substrate levels? And why?
No because it is binding to a different site
Inhibitor binds to a separate and distinct site
Uncompetitive inhibitor
Condition of uncompetitive inhibition
Can only bind to the site if the substrate is present
Irreversible inhibitors result in permanent inactivation of enzyme, why?
Because they form covalent bonds
In the Lineweaver-burk plot explain what happens to km and Vmax for competitive inhibition
Km is increased
Vmax is unaffected
In the Lineweaver-burk plot explain what happens to km and Vmax for non-competitive inhibition
Km is unaffected because inhibitor is not interfering with affinity of active site (it’s binding to a different site)
Vmax is reduced
In the Lineweaver-burk plot explain what happens to km and Vmax for uncompetitive inhibition
Km is reduced
Vmax is reduced
Covalent irreversible drugs
Bind specifically to drug target and form a precisely directed, permanent bond with their target
Example of therapeutic important enzyme inhibitors
Aspirin, penicillin, ace inhibitors, sildenafil, oseltamivir
ACE
Angiotensin converting enzyme
What does ACE do?
Key enzyme in converting angiotensin 1 to angiotensin 2 ( vasoactive hormone)
Ace inhibitor does what?
Inhibits ace from converting angiotensin 1 to2
What type of inhibitor is an ACE inhibitor?
Competitive inhibitor
Angiotensin 2 has effects that can do what to blood pressure?
Increase ( vasoconstriction)
Sildenafil also known as
Viagra
Sildenafil is what type of inhibitor?
Competitive inhibitor
What does sildenafil inhibit?
Phosphodiesterase V
What was sildenafil originally developed for?
Treatment for hypertension and angina
What was discovered about sildenafil at clinical trials?
Found to be effective at inducing erections than treating angina
How does sildenafil allow for more vasodilation?
Nitric oxide binds to receptors in smooth muscle cells which results in increased levels of cGMP
cGMP is broken down by phosphodiesterase V therefore using inhibitor increases levels of cGMP = more vasodilation
Oseltamivir also known as
Tamiflu
Oseltamivir is what type of inhibitor?
Competitive inhibitor
Oseltamivir inhibits what?
Viral neuraminidase
Function a viral neuraminidase
Prevents viral replication and release
Oseltamivir became a blockbuster how?
Through stockpiling for ‘swine flu’ pandemic of 2009
What is penicillin?
Group of drugs
What does penicillin inhibit?
Synthesis of bacterial peptidoglycan cell wall
Inhibition of cell wall synthesis by penicillin triggers what?
Action of autolytic enzymes by destabiling their cell wall located inhibitors
Key component of penicillin is?
Beta-lactam ring
Function of beta-lactams
Prevent cross-linking peptides from binding to the retrapeptide side chain so bacteria can’t form an efficient cell wall
Bacterial resistance can be achieved from penicillin how?
Action of beta-lactamases
(Ironically)
Aspirin can be used as both?
An anti-inflammatory (NSAID) and antiplatelet drug (blood thinner)
Therapeutic action happens by aspirin through which inhibition? And of what?
Irreversible inhibitor of enzyme cycloxygenase (COX)
Cox has 2 active sites
- Allows arachidonate acid to be converted to prostaglandin G2
- produce other prostaglandins
How does aspirin work as an anti-inflammatory?
Blocking cox reducesPG2 production which reduces production of prostanoids / pain-causing prostaglandins
How does aspirin work as an anti-platelet?
cox acts via glycoprotein receptors which cause platelets to clump together
Inhibition means less production of intermediate thromboxane a2 (from arachidonic)= less platelet aggregation
Example of protein mediators that can activate enzyme linked receptors
Growth factors, cytokines, hormones
Activation of enzyme-linked receptors enables binding and activation of many Intracellular signalling properties which do what?
Lead to changes in Gene transcription and in many cellular function
Characteristic of enzyme linked transmembrane receptors
-Large extracellcular binding domain
-Single transmembrane helical region
Feature of Receptor tyrosine kinase family
Ligand binding causes receptor dimerisation
- get either transphosphorylation or autophosphophorylation within the receptor itself
Activation of receptor serine/threonine kinase family does what?
Activation of these phosphorylates serine and threonine residues in target cytosolic proteins
Feature of cytokine receptors I non-receptor tyrosine kinase family
Lack integral kinase activity but activate separate kinases associated with the receptor
Feature of tyrosine phosphatase receptor family
Dephosphorylate tyrosines on other transmembrane receptors or cytoplasmic proteins, common in immune cells
Function of receptor guanylyl cyclase family
Catalyse the formation of cGMP from GTP via a cytosolic domain
Transduction mechanism for receptor tyrosine kinase
-Growth receptor binds to receptor domain(linked via alpha helix) which crosses over to a domain of the receptor (inside=tyrosine kinase)
- when growth factor binds in the active form, you get a conformational change which leads to dimerisation = starts auto/transphosphorylation of tyrosine kinase domains
- (intermediary) SH2-domain protein leads to a phosphorylation of it, the domain binding protein, when activates another protein called RAS which triggers a lot of steps
What is imatinib?
Protein kinase inhibitor
What is imatinib used for?
Used to increase years of those with chronic myelogenous leukaemia (CML)
Mechanism of action for imatinib
Directly inhibits protein kinase itself
By inhibiting the kinase, it blocks any downstream signalling and improves the outcome for patients
Everolimus (afinitor) used in treatment for?
Renal cell carcinoma (kidney cancer)
What type of inhibitor is everolimus?
Pan kinase inhibitor
Everolimus acts on what? And function?
Target of rapamycin (mTOR), which blocks the effect upon gene expression
Mechanism of action for Janus kinase inhibitors
Compete with ATP for the ATP binding sites on the kinase, preventing activation
JAK inhibitors = newest class of drugs to treat?
RA - rheumatoid arthritis
Leptin receptors are found where? Activation can result in?
Hypothalamus
- result in behavioural esteets upon feeding behaviour
Lepton used therapeutically for?
Losing weight in terms of obesity
In the hypothalamus, lepton can act as a satiety signaller what does this mean?
Activating these receptors mean you don’t feel as hungry, knock off effect on eating behaviour
Leptin is released from? What tissue?
Adipose tissue
Lipodystrophy vs healthy person
Healthy person- normal levels- normal regulation
Lipodystrophy-Reduced numbers of adipose tissue- reduced levels of lepton- reduction in inhibition of eating behaviour
Metrileptin (Recombinant form of leptin) function
Readdress the balance by stimulating more of these enzyme linked receptors
Which of the following drugs is an irreversible enzyme inhibitor of the enzyme COX?
Captopril, aspirin, penicillin, sildenafil ,oseltamivir
Aspirin
- most drug examples: reversible inhibitors of enzymes except aspirin and penicillin but aspirin irreversibly inhibits the COX enzyme
What is the function of dimerisation in kinase linked receptors?
Ennobles mutual autophosphorylation of tyrosine residues by tyrosine kinase
