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Biochemical Methods > Enzyme Inhibition > Flashcards

Enzyme Inhibition Flashcards

1
Q

What are chemicals that reduce the rate of enzymatic reactions?

A

Inhibitors

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2
Q

What are two types of enzyme inhibitors?

A

Irreversible and reversible

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3
Q

What type of inhibitor covalently modifies the active site of the enzyme irreversibly?

A

Irreversible

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4
Q

What type of inhibitor can be washed out of the solution of enzyme by dialysis?

A

reversible

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5
Q

What are the different types of reversible inhibitors?

A

1) Competitive
2) Uncompetitive
3) Non-competitive

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6
Q

What are two different types of non-competitive inhibtors?

A

pure; mixed

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7
Q

What residue does AchE use to prevent nerve gases and pesticides from getting utilized for catalysuis?

A

Serine

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8
Q

Which type of inhibition does the inhibitor structure closely resemble the substrate’s structure and competes for the active site of the enzyme with the substrate?

A

Competitive

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9
Q

Which type of inhibition does the inhibitor reduce the number of enzyme molecules available for the substrate?

A

Competitive

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10
Q

Which type of inhibition does the inhibitor increase the km but not the overall velocity (vmax does not change)?

A

Competitive

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11
Q

What is the equation for competitive inhibition?

A

vo=(Vmax[S])/(alphaKm + [S])

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12
Q

What is the dissociation constant of EI in competitive inhibition?

A

Ki= [E][I]/[EI]

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13
Q

What is alpha and what is its equation?

A

the degree of inhibition

alpha = 1 + ([I]/Ki)

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14
Q

In competitive inhibition, the LB-plot slope increases as what increases?

A

the degree of inhibition (alpha)

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15
Q

What example for competitive inhibition was given in class?

A

Methotrexate competitively inhibits dihydrofolate reductase (DHFR) (inhibits DNA synthesis)

HIV Protease Inhibitors (HIV Protease cleaves Phe-Pro bond

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16
Q

How do you determine Ki for competitive inhibition?

A

1) plot I/vo vs 1/[S] (LB-plot) for different Is
2) find the slope of each line produced
3) plot the slope of the lines vs [I]
4) the x-intercept is -Ki (in concentration units)

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17
Q

How do you overcome competitive inhibition?

A

by increasing the concentration of the substrate [S] Vmax can be attainable

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18
Q

What example of overcoming competitive inhibition was given in class?

A

methanol or ethylene glycol poisoning, patients are given ethanol

methanol gets converted to formaldehyde instead of acetic acid (ethanol gets converted to acetic acid)

methanol is excreted in the urine if out-competed by ethanol

19
Q

When this binds to an enzyme it completely distorts the active site rendering the enzyme catalytically innactive. What is it?

A

An uncompetitive enzyme

20
Q

In uncompetititve inhibition, the inhibitor affects what but not what?

A

the catalytic function of the enzyme; the substrate binding

21
Q

Vmax and km are reduced by the same extent in what type of inhibition?

A

Uncompetitive

22
Q

What is the Michaelis-Menton equation for uncompetitive inhibition?

A

vo=(Vmax[S])/(Km+alpha’[S])

23
Q

What is the dissociation constant for ESI?

A

K’i = ([ES][I])/[ESI]

24
Q

What is the degree of inhibition for uncompetitive inhibition?

A

alpha’ = 1 + ([I]/K’i)

25
Q

Does the slope change in uncompetitive inhibition?

A

No

26
Q

Can the effect of the uncompetitive inhibitor be abolish by increasing [S]?

A

No

27
Q

What was an example of an uncompetitive inhibitor given in class?

A

Round up- interferes with the synthesis of the aromatic amino acids

28
Q

How do you find Ki for uncompetitive inhibition?

A
  1. plot I/vo vs 1/[S]
  2. plot the slopes of the lines formed vs [I]
  3. -K’i = to the x-intercept
29
Q

What kind of inhibitor can bind to the free enzyme as well as the enzyme/substrate complex and affects both substrate binding and catalysis?

A

Non-competitive

30
Q

The non-competitive inhibitor binds to E and ES but may have a greater affinity for what?

A

one over the other

31
Q

If the binding affinity of the non-competitive inhibitor to free enzyme equals the binding affinity to the enzyme/substrate complex, the inhibition is considered what?

A

Pure

32
Q

If the binding affinity of the non-competitive inhibitor to free enzyme does not equal the binding affinity to the enzyme/substrate complex, the inhibition is considered what?

A

Mixed

33
Q

If pure, alpha equals what?

A

alpha’

34
Q

What is the Michaelis-Menton equation for non-competitive inhibition?

A

vo = to (vmax[S])/(alphaKm +alpha’[S])

35
Q

With pure non-competitive inhibition, what happens to vmax, km, and the slope?

A

Vmax decreases, km remains the same, the slope changes

36
Q

With mixed non-competitive inhibition, what happens to vmx, km, and the slope?

A

Vmax decreases, Km changes, the slope changes

37
Q

What example of non-competitive inhibition was given in class?

A

Heavy metal poisoning

38
Q

How do you find Ki and K’i for non-competitive inhibition?

A

1) LB plot (1/vo) vs 1/[S] at different [I]
2. plot the slopes of the LB plots vs [I] to find -Ki (x-intercept)
3) plot y-intercept vs [I} to find -K’i (x-intercept)

39
Q

In which type of inhibition does vmax stay the same?

A

competitive

40
Q

Does Vmax increase or decrease for uncompetitive and noncompetitive inhibition?

A

decrease

41
Q

Does Km increase or decrease with competitive inhibition?

A

increase

42
Q

Does Km increase or decrease with uncompetitive inhibition?

A

decrease

43
Q

Does Km increase or decrease with non-competitive inhibition?

A

it can increase or decrease

44
Q

In non-competitive inhibition, can the products formed by the inhibitor interact?

A

yes

Biochemical Methods (5 decks)

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