Lecture 3. Effects of pH and T on Enzyme Activity and Enzyme Inhibitors and Inhibition Flashcards
What are the axes for an Eadie-Hofstee plot?
x axis = v/[S]
y axis = v
On an Eadie-Hofstee plot, what does the y-intercept represent?
Vmax
On an Eadie-Hofstee plot, what does the x-intercept represent?
Vmax/Km
On an Eadie-Hofstee plot, what does the gradient represent?
-Km
When temperature increases, what happens to the rates of enzyme-catalysed reactions?
The rates of enzyme-catalysed reactions increase
What is Q10 generally for biological reactions?
2 - the rate doubles for every 10 degree rise in temperature
What enzymes do not denature at high temperatures?
Enzymes derived from organisms living in hot environments and enzymes from thermophiles
What enzyme is used in PCR?
Taq polymerase
What does the pH-dependence of an enzyme’s activity reflect?
The ionisation of groups on S and in the active-site of E
What can pH affect?
Both Km and kcat
What can pH-dependence provide useful insights into?
pH-dependence can provide useful insights into the
nature of groups (amino acid side chains) involved in the
active site
What is ACE?
Angiotensin-converting enzyme
What is an example of an ACE inhibitor?
Enalapril
What are ACE inhibitors used for?
Treatment of hypertension, diabetic nephropathy, and some types of chronic heart failure
How do ACE inhibitors work?
ACE inhibitors lower blood pressure by blocking production of a signal promoting blood vessel contraction
How does aspirin work?
Aspirin inhibits an enzyme that produces prostaglandin, blocking the inflammatory response
How does penicillin work?
Penicillin inhibits enzymes which enable bacteria to make stable, robust, cross- linked cell walls. It fixes the enzyme in the ES complex
What do many drugs target?
Enzymes
What is an example of a receptor targeting drug?
Beta-blockers
How do Beta-blockers work?
Beta-blockers bind and inhibit the action of noradrenaline on β-adrenergic receptors
How does irreversible enzyme inhibition occur?
When an inhibitor reacts covalently with essential active sites
What are examples of irreversible inhibitors?
Organomercurials and nerve gas
What do organomercurials target?
Cys residues
What does nerve gas target?
Reactive Ser residues
What does mercury inhibit?
Selenoenzymes
How does iodoacetamide inactivate enzymes?
Iodoacetamide inactivates enzymes by reacting with critical cysteine residues
How does DIPF inactivate enzymes?
DIPF is a nerve gas; it inactivates acetylcholinesterase by reacting with a highly reactive serine in the active site
What are two types of reversible inhibitors?
Competitive and non-competitive
How do competitive inhibitors function?
Competitive inhibitors act by blocking substrate binding
(they compete with S to bind to E) and are often
structural homologues of S
How do non-competitive inhibitors function?
Non-competitive inhibitors bind at same time as S, but
not in the same site, and act by slowing down
conversion to P
What does competitive inhibition imply at very high [S]?
S will displace I; therefore, even in the presence of I E will become saturated with S
What is oseltamivir?
A competitive inhibitor of neuraminidase. It mimics a natural substrate acetyl sialic acid
What are the effects of a competitive inhibitor on Vmax and Km?
A competitive inhibitor has no effect on V max but increases Km
What are the effects of a non-competitive inhibitor on Vmax and Km?
A non-competitive inhibitor decreases Vmax but has no effect on Km
What graph would you plot to distinguish competitive from non-competitive inhibitors?
Lineweaver-Burk plot
