Enzymes As Drug Targets

Question 1

Define: V_max

Answer 1

The maximum rate at which an enzyme can carry out a reaction

Question 2

Define: K_m

Answer 2

The substrate concentration at which the enzymes will work at 1/2 of Vmax

Question 3

What is plotted on a Lineweaver-Burke plot?

Answer 3

Reciprocals: 1/V and 1/[S]

Question 4

What does the intercept on the y axis of a Lineweaver-Burke plot indicate?

Answer 4

1/V_max

Question 5

What does the intercept on the x axis of a Lineweaver-Burke plot indicate?

Answer 5

-(1/K_m)

Question 6

What is an issue with just plotting initial reaction rate vs substrate concentration to calculate Vmax and Km?

Answer 6

The eventual substrate concentration reached for the V_max is actually quite difficult to reach - end up saturating the reaction

Question 7

What does the gradient of a Lineweaver-Burke plot indicate?

Answer 7

= K_m/V_max

Question 8

Define: K_i

Answer 8

A constant - describes how frequently an inhibitor will bind to the enzyme

Question 9

Define: K’_i

Answer 9

A constant - describes how frequently an inhibitor will bind to an ES complex

Question 10

Define: Competitive inhibition

Answer 10

Where an inhibitor binds to an enzyme’s active site to prevent the substrate from binding. It is usually reversibly bound

Question 11

What happens to the V_max, K_m and gradient of an L-B plot when a competitive inhibitor is introduced?

Answer 11

• The gradient becomes steeper
• V_max stays the same (as long as enough substrate)
• K_m is altered

Therefore less substrate is processed and a higher concentration of substrate is required to reach 1/2V_max

Question 12

What happens to the V_max, K_m and gradient of an L-B plot when a non-competitive inhibitor is introduced?

Answer 12

• The gradient becomes steeper
• V_max is altered
• K_m stays the same

This is because there is a smaller enzyme population = lower V_max

Question 13

Define: non-competitive inhibitor

Answer 13

Bind directly to the active site, are irreversibly bound

Question 14

What is prevented when viral enzymes are targeted by drugs?

Answer 14

Prevents viral replication

Question 15

What do bactericidal drugs target?

Answer 15

Enzymes produced by bacteria that are not found or are different in humans = specificity

Question 16

What do DD transpeptidases do?

Answer 16

Carry out crosslinking of peptidoglycan wall subunits for bacteria (Also known as penicillin binding protein, PBP)

Question 17

What type of drug targets DD transpeptidases?

Answer 17

Beta lactam antibiotics

Question 18

How do beta lactam antibiotics kill bacteria cells?

Answer 18

1. The antibiotics bind to and irreversibly inhibit DD transpeptidase (which cross-links the peptidoglycan wall units)
2. Bacterium cannot split into 2 daughter cells with cell walls
3. Therefore, a spheroplast is formed (no cell wall) and cell will burst

Question 19

Name the enzyme that counteracts beta lactam antibiotics

Answer 19

Beta lactamases give the bacteria antibiotic resistance = enzymatic defence system

Question 20

What does HIV protease do in a virus molecule?

Answer 20

Processes (cleaves) viral virion proteins required for the formation of the active virus

Question 21

Name a drug that targets HIV protease

Answer 21

Atazanavir

Question 22

What organ is ACE (angiotensin converting enzyme) responsible for regulating?

Answer 22

The kidney

Question 23

What is the mechanism of action of ACE?

Answer 23

ACE acts as a protease, cleaving angiotensin I and converting it into angiotensin II = the active form of the peptide

Question 24

Name the enzyme that converts angiotensinogen to angiotensin I

Answer 24

Renin

Question 25

What enzymatic conversion process is renin responsible for?

Answer 25

Converting angiotensinogen to angiotensin I

Question 26

Name the enzyme that Ramipril targets

Answer 26

ACE

Question 27

Name the drug that targets ACE

Answer 27

Ramipril

Question 28

What is Ramipril’s mechanism of action?

Answer 28

1. Ramipril inhibits the proteolytic activity of ACE
2. So the production of Angiotensin II is decreased
3. This decreases fluid retention
4. Resulting in lower blood pressure

Question 29

What condition is Ramipril prescribed for?

Answer 29

High BP

Question 30

What does COX stand for?

Answer 30

Cyclo-oxygenase

Question 31

Define: cyclo-oxygenase

Answer 31

Enzymes which are responsible for the production of prostaglandins (important for inflammatory response)

Question 32

What is the mechanism of action of Ibuprofen?

Answer 32

1. Binds to the active site of COX enzymes
2. Prevents the substrate (arachidonic acid) binding
3. Inhibits the production of prostaglandins
4. Inflammation and pain are reduced

Question 33

How do kinases regulate the activity of proteins?

Answer 33

By altering their structure using the addition of a phosphate group

Question 34

Define: allosteric modulation

Answer 34

When a substance indirectly influences (modulates) the effects of the agonist at a target protein (i.e. enzyme)

Question 35

How does allosteric binding alter the function of an enzyme?

Answer 35

• The allosteric substrate alters the overall protein shape when it binds
• This can lead to altered substrate binding or active site function

Question 36

How does ‘co-operative activity’ change the shape of a r/r vs [S] curve?

Answer 36

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

Question 37

Define: co-operative activity/binding

Answer 37

Occurs in complexes made up of several molecules

1. A ligand binds to one of the molecules
2. The overall shape of the protein is altered
3. The other active sites of the complex are altered so they are more likely to pick up the ligand
4. Affinity increased

Question 38

Give an example of co-operative binding

Answer 38

Haemoglobin: made up of multiple molecules of beta globin, when oxygen binds affinity for O2 increases

Question 39

Name 3 ways that allosteric binding can change an enzyme to make a reaction more likely

Answer 39

1. AS opening
2. Formation of AS
3. Enhancement of dimerisation (binding of 2 proteins/enzymes creates an AS)

^^ All due to allosteric binding of a ligand

Question 40

Name 3 ways that allosteric binding can change an enzyme make a reaction less likely

Answer 40

1. AS closing
2. Active site distortion
3. Inhibition of dimerisation (prevents, blocks)

^^ All due to allosteric binding of a ligand