FIII: Lecture Slides 58 - 68

Question 1

What are inactivators?

Answer 1

Act on an enzyme irreversibly

Question 2

What does inactivation result from?

Answer 2

Inactivation results from a covalent chemical reaction between the inactivator and the enzyme

Question 3

Why is inactivation irreversible?

Answer 3

Due to the reaction destroying catalytic activity and the enzyme being used up.

Question 4

What is the simple stoichiometric equation between the inactivator and the enzyme?

Answer 4

2 umol inactivator and 3 umol enzyme = 1 umol of active enzyme left

Question 5

What are inactivators considered to be?

Answer 5

Extremely toxic (Example: nerve gases have the ability to inactivate acteylcholinesterase which then interferes with nerve impulses)

Question 6

What are inhibitors?

Answer 6

Bind to enzymes irreversibly

Question 7

What can an inhibitor do?

Answer 7

Decrease enzyme activity without destroying the catalytic function of enzyme molecule

Question 8

What happens when the inhibitor concentration is removed?

Answer 8

The enzyme activity is restored

Question 9

What type of reaction is inhabitation?

Answer 9

Binding equilibrium, as it can be reversed.

Question 10

Competitive Inhibition

Answer 10

Where the inhibitor binds to the active site on the enzyme, where the substrate would bind (competing with substrate for active site)

Question 11

Non-competitive Inhibition

Answer 11

Inhibition affects the catalytic rate, the inhibitor binds at an allosteric site separate from the active substrate binding site

Question 12

What are inhibitors main job?

Answer 12

To regulate enzyme activity in a cell.

Question 13

What is an example of two drugs that are inhibitors?

Answer 13

Aspirin and Advil:
Both drugs inhibit the cyclooxyrgenase enzyme that make prostaglandins: affect inflammatory response.

Question 14

When can competitive inhibitors bind?

Answer 14

When the enzyme E is unoccupied (not with a substrate)

Question 15

What is the inhibitor binding constant?

Answer 15

Ki

Question 16

What does Ki equal?

Answer 16

[E][I]/[EI]

Question 17

What is the reaction of an enzyme plus an inhibitor?

Answer 17

E + I —-> (rev) EI

Represented by Ki

Question 18

What does the formation of the EI complex mean?

Answer 18

The formation means that there is less enzyme available to bind substrate

Question 19

What can high [S] do?

Answer 19

Outcompete the competitive inhibitor

Question 20

Why might the substrate and inhibitor have resemblance?

Answer 20

Because they share the same binding site, they may resemble each other in terms of chemical structure.

Question 21

What happens when you graph enzyme behaviour in presence of competitive inhibitor vs. substrate when you keep [I] constant

Answer 21

The Km of the inhibitor is increased.

Question 22

What is the equation for Km of Inhibitor?

Answer 22

Km’ = Km(1 + [I]/Ki)

Question 23

What is Ki?

Answer 23

A characteristic constant for each inhibitor

Question 24

What is the inhibition factor?

Answer 24

1 + [I]/Ki

Question 25

What is Ki in terms of Km for competitive inhibition?

Answer 25

The concentration of inhibitor [I] that causes Km to double.

Question 26

How can competitive inhibition be seen with a Lineweaver-Burk Plot?

Answer 26

• There is no effect on Vmax, so all graphs have same Y-intercept (y-int = 1/Vmax)
• Km’ increases as [I] increases so your x-intercepts get smaller (x-int = -1/Km)
• Slope increases as [I] increases: LB slope = Km’/Vmax

Question 27

Where can non-competitive inhibitors arise?

Answer 27

Non-competitive inhibition can bind to both Enzyme or Enzyme-Substrate Complex

Question 28

When a non-competitive inhibitor binds, what two complexes can they form?

Answer 28

They can form an EIS and an EI complex?

Question 29

What does the formation of EI and EIS mean?

Answer 29

Less ES to undergo catalysis but substrate can still bind to EI without yielding product.

Question 30

What might the bound inhibitor do?

Answer 30

Disorganize the catalytic component of the enzyme

Question 31

When might you get mixed inhibition?

Answer 31

If EI and EIS have a different Ki

Question 32

What happens in a Michael Menten plot of Non-Competitive Inhibition?

Answer 32

• Vmax decreases as [I] increases: V’max = Vmax/1 + [I]/Ki
• Km is unchanged
• If [I] is set equal to Ki, inhibition factor = 2

Question 33

What is Ki for non-competitive inhibition?

Answer 33

Ki is the concentration of inhibitor [I] that causes Vmax to halve

Question 34

Non-competitive Inhibition on a Lineweaver Plot:

Answer 34

• No effect on Km so all graphs have same X-inter: -1/km
• Vmax decreases as [I] increases so y -intercept: 1/Vmax
• Slope increases as [I] increases; LB slope = Km/V’max

For mixed inhibition, lines meet above the X-Axis.