Lecture 3. Effects of pH and T on Enzyme Activity and Enzyme Inhibitors and Inhibition

Question 1

What are the axes for an Eadie-Hofstee plot?

Answer 1

x axis = v/[S]
y axis = v

Question 2

On an Eadie-Hofstee plot, what does the y-intercept represent?

Answer 2

Vmax

Question 3

On an Eadie-Hofstee plot, what does the x-intercept represent?

Answer 3

Vmax/Km

Question 4

On an Eadie-Hofstee plot, what does the gradient represent?

Answer 4

-Km

Question 5

When temperature increases, what happens to the rates of enzyme-catalysed reactions?

Answer 5

The rates of enzyme-catalysed reactions increase

Question 6

What is Q10 generally for biological reactions?

Answer 6

2 - the rate doubles for every 10 degree rise in temperature

Question 7

What enzymes do not denature at high temperatures?

Answer 7

Enzymes derived from organisms living in hot environments and enzymes from thermophiles

Question 8

What enzyme is used in PCR?

Answer 8

Taq polymerase

Question 9

What does the pH-dependence of an enzyme’s activity reflect?

Answer 9

The ionisation of groups on S and in the active-site of E

Question 10

What can pH affect?

Answer 10

Both Km and kcat

Question 11

What can pH-dependence provide useful insights into?

Answer 11

pH-dependence can provide useful insights into the
nature of groups (amino acid side chains) involved in the
active site

Question 12

What is ACE?

Answer 12

Angiotensin-converting enzyme

Question 13

What is an example of an ACE inhibitor?

Answer 13

Enalapril

Question 14

What are ACE inhibitors used for?

Answer 14

Treatment of hypertension, diabetic nephropathy, and some types of chronic heart failure

Question 15

How do ACE inhibitors work?

Answer 15

ACE inhibitors lower blood pressure by blocking production of a signal promoting blood vessel contraction

Question 16

How does aspirin work?

Answer 16

Aspirin inhibits an enzyme that produces prostaglandin, blocking the inflammatory response

Question 17

How does penicillin work?

Answer 17

Penicillin inhibits enzymes which enable bacteria to make stable, robust, cross- linked cell walls. It fixes the enzyme in the ES complex

Question 18

What do many drugs target?

Answer 18

Enzymes

Question 19

What is an example of a receptor targeting drug?

Answer 19

Beta-blockers

Question 20

How do Beta-blockers work?

Answer 20

Beta-blockers bind and inhibit the action of noradrenaline on β-adrenergic receptors

Question 21

How does irreversible enzyme inhibition occur?

Answer 21

When an inhibitor reacts covalently with essential active sites

Question 22

What are examples of irreversible inhibitors?

Answer 22

Organomercurials and nerve gas

Question 23

What do organomercurials target?

Answer 23

Cys residues

Question 24

What does nerve gas target?

Answer 24

Reactive Ser residues

Question 25

What does mercury inhibit?

Answer 25

Selenoenzymes

Question 26

How does iodoacetamide inactivate enzymes?

Answer 26

Iodoacetamide inactivates enzymes by reacting with critical cysteine residues

Question 27

How does DIPF inactivate enzymes?

Answer 27

DIPF is a nerve gas; it inactivates acetylcholinesterase by reacting with a highly reactive serine in the active site

Question 28

What are two types of reversible inhibitors?

Answer 28

Competitive and non-competitive

Question 29

How do competitive inhibitors function?

Answer 29

Competitive inhibitors act by blocking substrate binding (they compete with S to bind to E) and are often structural homologues of S

Question 30

How do non-competitive inhibitors function?

Answer 30

Non-competitive inhibitors bind at same time as S, but not in the same site, and act by slowing down conversion to P

Question 31

What does competitive inhibition imply at very high [S]?

Answer 31

S will displace I; therefore, even in the presence of I E will become saturated with S

Question 32

What is oseltamivir?

Answer 32

A competitive inhibitor of neuraminidase. It mimics a natural substrate acetyl sialic acid

Question 33

What are the effects of a competitive inhibitor on Vmax and Km?

Answer 33

A competitive inhibitor has no effect on V max but increases Km

Question 34

What are the effects of a non-competitive inhibitor on Vmax and Km?

Answer 34

A non-competitive inhibitor decreases Vmax but has no effect on Km

Question 35

What graph would you plot to distinguish competitive from non-competitive inhibitors?

Answer 35

Lineweaver-Burk plot