L15 - enzymes as drug targets

Question 1

simple models of reversible enzyme inhibition assume?

Answer 1

1. only one molecule of inhibitor will bind to one molecule of enzyme
2. inhibitor binding is reversible
3. linear kinetics will be observed (ROR will not change except for when substrate is added/removed)
4. inhibitors are dead end (at saturated inhibitor conc there will be no residual enzymes activity)

Question 3

mode of action of inhibitors

Answer 3

1. inhibitors can resemble the substrate
2. inhibitors can effect Km, Vmax
3. potency is measured by Ki fable
4. Ki values relate to binding energy (ΔG)
5. smaller Ki numbers mean higher binding (higher potency)

Question 4

what is Ki?

Answer 4

conc of inhibitor that causes 2 fold change in Km or Vmax

Question 5

what do many potent inhibitors resemble?

Answer 5

transition state of a reaction

Question 6

to make new inhibitors what do you need to know?

Answer 6

enzyme mechanism

Question 7

competitive inhibition

Answer 7

• most common
• Km increases (x-intercept changes)
• Km (I) = Km (1 + [I]/Ki)
• km in presence of inhibitor = km in absence x (1 x inhibitor conc / ki value)
• no change in Vmax (y intercept stays same)
• inhibition decreases with increased substrate concentration

Question 8

non competitive inhibition

Answer 8

• uncommon for single substrate enxymes
• Vmax is reduced
• Vmax/Km (I) = Vmax/Km(1 + [I]/Ki)
• Km not affected
• inhibition not reduced by increasing substrate

Question 9

mixed competitive

Answer 9

• common form inhibiton
• Km increases
• Vmax decreases
• α factor defines balance of the competitive and non-competitive components.

Question 10

uncompetitive inhibitor

Answer 10

• uncommon
• inhibitor binds to ES complex
• parallel lines in lineweaver burk plot
• Km and Vmax decrease by same amount , (1 + [I]/Ki)
• increasing substrate concentration increases inhibition

Question 11

dose response curves (aka IC50 curves)

Answer 11

• measures drug potency at a fixed substrate concentration
• IC50 = conc of drug needed to reduce activity by 50%
• value depends on assay conditions
• IC50 not same as Ki

Question 12

when does tight binding inhibition occur?

Answer 12

when conc of active enzyme and inhibitor are similar

Question 13

if conc of active enzyme and inhibitor are similar what does this mean?

Answer 13

conc of free inhibitor does not equal to total inhibitor

Question 14

in tight binding inhibitors, what does ki value increase with?

Answer 14

enzyme concentration

Question 15

info about tight binding inhibition

Answer 15

• slow onset
• enzyme inhibitor complex can have longer half life ((Ki = koff/kon)
• so infrequent dosage regimes can be used