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Biochemistry > Chapter 7.5 Enzyme Regulation > Flashcards

Chapter 7.5 Enzyme Regulation Flashcards

1
Q

what is inhibition?

A

inactivation of enzymatic function

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2
Q

what do enzyme inhibitors usually mimic? (2)

A

either the transition state or the substrate

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3
Q

what are the 2 types of inhibition?

A
  1. irreversible
  2. reversible
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4
Q

describe irreversible inhibition (2)

A
  1. covalent bonding or strong non-covalent bonds
  2. non-dilutable
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5
Q

describe reversible inhibition (2)

A
  1. noncovalent bonds
  2. dilutable
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6
Q

how does irreversible inhibition work? (2)

A
  1. molecules covalently bond to amino acid side chains and the active site is changed to a nonfunctional conformation
  2. molecules bind to the nonfunctional active site become trapped and disallow substrate binding
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7
Q

give an example of an irreversible protease inhibitor; describe what is blocks how it works (2)

A

diisopropylfluorophosphate (DFP)
1. blocks protease and phsopholipase enzymes
2. forms a covalent bond with reactive serine residues and renders the enzymes useless

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8
Q

what are the 3 types of reversible inhibition?

A
  1. competitive inhibition
  2. uncompetitive inhibition
  3. mixed inhibition
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9
Q

how do competitive inhibitors work?

A

compete with the substrate for the active binding site; if they win they block the acgive site

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10
Q

what happens to competitive inhibitors eventually?

A

they will eventually dissociate

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11
Q

what does the level of inhibition of competitive inhibitors depend upon? (2)

A

concentration of both
1. substrate [S] and
2. inhibitor [I]

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12
Q

what competitive inhibitor mimics succinate ligand?

A

malonate

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13
Q

what is malonate and what does it do?

A

a competitive inhibitor that competes with the substrate to bind succinate dehydrogenase enzyme

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14
Q

what does competitive inhibition do to Km substrate binding and why?

A

since higher substrate [S] is needed to reach 1/2 Vmax, Km APPEARS to increase to Km-app and substrate binding appears to be weaker

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15
Q

what may some apo/free enzymes form in the presence of competitive inhibitors?

A

may form [EI] (enzyme-inhibitor complexes) instead of [ES]

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16
Q

what can overcome the inhibitory effects of competitive inhibitors?

A

high [S]

17
Q

do competitive inhibitors alter Vmax?

A

nope

18
Q

on reaction velocity plots of competitive inhibition, what happens to Km?

A

higher Km, closer to origin on LWB plots

19
Q

what does uncompetitive inhibition do to Km and Vmax?

A

lowers both!!

20
Q

describe uncompetitive inhibition (3)

A
  1. inhibitor binds away from the active site (NO COMPETE)
  2. inhibitor binds [ES] complex and alters the active site
  3. some [S] is wasted since the inhibitor binds [ES] and [S] doesn’t dissociate
21
Q

what explains what looks like an extra state in uncompetitive inhibition?

A

it looks like the substrate is bound long, but really the substrate just is not dissociating from the [ESI] complex

22
Q

describe the slopes on LWB plots with uncompetitive inhibition (also the Vmax and Km)

A

Km and Vmax are decreased, but the slopes are parallel becayse the overall slope remains the same no matter the level of inhibitor

23
Q

what does mixed inhibition do to Vmax and Km?

A
  1. decreases Vmax
  2. decreases or increases Km
24
Q

describe mixed inhibitions (3)

A
  1. binds away from the active site
  2. binds free enzyme or [ES] complex
  3. causes a conformational change that affects substrate binding (this moves Km up or down)
25
Q

what is Ki?

A

the binding affinity of inhibitor for enzyme

26
Q

what is Ki’?

A

binding affinity of inhibitor for enzyme-substrate complex

27
Q

what is noncompetitive inhibition?

A

a type of mixed inhibition

28
Q

what does noncompetitive, mixed inhibition do to Vmax and Km?

A
  1. decreases Vmax
  2. DOES NOT CHANGE Km
29
Q

dedscribe noncompetitive mixed inhibition

A
  1. doesn’t bind active site
  2. causes a conformational change that affects the active site without substrate binding
30
Q

relate Ki and Ki’ in noncompetitive, mixed inhibition

A

Ki=Ki’

31
Q

describe what happens to Kcat in regular mixed and noncompetitive mixed inhibition

A

Kcat decreases in all types of mixed inhibition

32
Q

what does Vmax equal in terms of Kcat and [Et]?

A

Vmax = Kcat * [Et]

Biochemistry (20 decks)

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