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Biochem 1 (WPH) > Enzymes 3 - inhibition & regulation Spencer > Flashcards

Enzymes 3 - inhibition & regulation Spencer Flashcards

1
Q

T/F covalent interactions bind reversible inhibitors to enzymes

A

false - non-covalent interactions

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2
Q

how does reversible inhibition alter michelis-menten kinetics?

A

Vm and Km can be altered into Vm apparent and Km apparent

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3
Q

what is the dissociation constant for the EI complex in competitive inhibition

A

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

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4
Q

how does competitive inhibition change the michelis-menten plot?

A

same Vm
increased Km by a factor of 1+[I]/Ki
so lower hyperbolic takes longer to reach same Vm

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5
Q

how does competitive inhibition change the lineweaver-burke plot?

A

same Vm so same y-intercept

higher Km so decreased x-intercept and increased slope (lower catalytic efficiency)

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6
Q

how does competitive inhibition change catalytic efficiency?

A

decreases it

higher Km so kcat/Km is lower

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7
Q

what is the michelis-menten equation for a competitively inhibited enzyme reaction?

A

v0 = VmS / [Km(1+I/Ki) + S]

where Ki = dissociation constant for EI

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8
Q

how does competitive inhibition work?

A

inhibitor mimics shape and structure of substrate or transition state but lacks functionality for reaction – competes with substrate at the binding site.

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9
Q

T/F competitive inhibitors include both substrate analogs and transition state analogs

A

true

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10
Q

which are more potent inhibitors, substrate analogs or transition state analogs?

A

transition state analogs - bind more tightly to enzyme

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11
Q

what kind of reversible inhibitors bind to free enzyme only

A

competitive

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12
Q

what kind or reversible inhibitors bind to the ES complex only

A

uncompetitive

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13
Q

what kind of reversible inhibitors bind to E or ES complex

A

noncompetitive

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14
Q

what kind of reversible inhibitor binds only after substrate is bound?

A

uncompetitive

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15
Q

what is the michelis-menten equation for uncompetitive inhibition?

A

v0 = Vm/(1+I/Ki)S / [Km/(1+I/Ki) + S]

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16
Q

how does uncompetitive inhibition alter the michelis-menten plot?

A

lower Vm
lower Km
slopes are similar at low [S] (no gap)

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17
Q

how does uncompetitive inhibition alter the lineweaver-burke plot?

A

slopes are same (Km/Vm is same)
1/Vm increases (y-int up)
-1/Km more negative (x-int left)

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18
Q

how does uncompetitive inhibition alter catalytic efficiency?

A

does not alter it
kcat and Km decrease by same factor
just like taking E out of system, not affecting catalytic mechanism

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19
Q

which kind of reversible inhibition is the rarest, competitive, uncompetitive, or noncompetitive?

A

uncompetitive

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20
Q

how do uncompetitive inhibitors work?

A

bind to ES complex and hinder reaction (apparently increase E + S affinity by taking ES out of solution and driving reaction right)

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21
Q

how does noncompetitive inhibition work?

A

bind to allosteric site and inhibit catalytic mechanism (does not affect E + S binding)

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22
Q

how does noncompetitive inhibition alter the michelis-menten plot?

A

Vm is decreased
Km is same
slopes diverge from start (gap)

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23
Q

what is the michelis-menten equation for non-competitive inhibition?

A

v0 = Vm/(1+I/Ki)S / (Km + S)

24
Q

how does noncompetitive inhibition alter the lineweaver-burke plot?

A 
x-intercept remains same (-1/Km is same)
y-intercept up (1/Vm increases)
slope increases (Km/Vm increases)
25
Q

how does noncompetitive inhibition affect catalytic efficiency?

A

decreases it
kcat down
Km same
kcat/Km down

26
Q

which type of reversible inhibition does not affect E + S binding?

A

noncompetitive

only affects catalytic mechanism

27
Q

which type of reversible inhibitor can be overcome by increasing [S]?

A

competitive

28
Q

what are the main differences between michelis-menten plots for uncompetitive and non-competitive inhibition?

A 
uncompetitive = no early gap, lower Km
noncompetitive = early gap, same Km
29
Q

conceptually, why does uncompetitive inhibition lower Km?

A

because [I] effectively takes some

30
Q

which reversible inhibitor binds only to:
E
ES
E or ES

A

competitive
uncompetitive
noncompetitive

31
Q

conceptually, why do uncompetitive inhibitors lower Km?

A

remove ES from solution, drive reaction right, increasing apparent E + S affinity

32
Q

conceptually, why do noncompetitive inhibitors not lower Km?

A

remove E and ES from solution at equal rates, so does not drive reaction either direction by Le Chatlier’s principle

33
Q

how does irreversible inhibition work?

A

inhibitor covalently binds to free E, often at active site but sometimes not, effectively removing [E] from solution

34
Q

3 categories of irreversible inhibitors

A

group-specific
affinity labels
suicide inhibitors

35
Q

how does irreversible inhibition affect Vm and Km?

A

decrease Vm

no change Km

36
Q

what is the main difference between group-specific, affinity label, and suicide irreversible inhibitors?

A

specificity to the active site

  • group-specific can bind active or allosteric site
  • affinity labels bind active site
  • suicide inhibitors bind active site; tricks enzyme into reaction that permanently modifies
37
Q

which irreversible inhibitors are substrate analogs?

A

affinity labels and suicide inhibitors

group-specific reagents do not always bind active site

38
Q

T/F allosteric enzymes do not fit the michaelis-menten model

A

true - usually sigmoidal v0 vs [S] relationship

39
Q

what is a homotropic effector

A

a substrate that allosterically affects enzyme activity (usually increases it)

40
Q

what is a heterotropic effector

A

an allosteric effector that is not the same as the enzyme substrate

41
Q

T/F allosteric enzymes are always oligomers

A

false - they are Usually oligomers (interaction on one subunit affects others) but some monomeric allosteric enzymes do exist

42
Q

how do regulatory proteins work in the case of PKA

A

regulatory proteins block active site of PKA until cAMP binds regulatory subunit and unblocks

43
Q

what is reversible covalent modification

A

enzymes covalently modified by adding charged groups (phosphate, sulfate, acetate) that cause conf change an activation or inactivation (e.g. phosphorylation)

44
Q

what is proteolytic activation

A

activating an enzyme by irreversibly cleaving part of the molecule away

45
Q

reversible inhibition, irreversibile inhibition, allosteric control, regulatory proteins, reversible covalent modification, and proteolytic activation are all forms of…

A

enzyme inhibition and/or control

46
Q

T/F enzymes under allosteric control are usually rate-determining enzymes in metabolic pathways

A

true

47
Q

does allosteric regulation involve covalent or non-covalent binding?

A

non-covalent

48
Q

T/F phosphorylation with a kinase is the reverse of dephosphorylation with a phosphatase

A

false - the net reaction is
ATP + H2O -> ADP + Pi
kinase does not generate H2O
phosphatase does not generate ATP

49
Q

T/F target proteins can cycle in either direction from unphosphorylated to phosphorylated using either phosphatase or kinase

A

false - phosphatase and kinase only work in one direction each

50
Q

T/F phosphorylation and dephosphorylation are each reversible reactions

A

false - k3 / kcat only, very little to no k4

51
Q

T/F the overall phosphorylation/dephosphorylation cycle results in hydrolysis of ATP

A

true - ATP is not regenerated by dephosphorylation – Pi is the product

52
Q

T/F the overall phosphorylation cycle has a free energy change greater than zero

A

false - ∆G < 0
ATP + H20 -> ADP + Pi
reactants are higher energy than products

53
Q

if given a question gives v initial and v final for two different substrate concentrations with and without inhibitor, how do you know what kind of inhibitor it is?

A

vf/vi inhibited = vf/vi normal, noncompetitive
vf/vi inhibited < vf/vi normal, competitive
vf/vi inhibited > vf/vi normal, uncompetitive

54
Q

what is difference between noncompetitive inhibitor and negative allosteric effector?

A

noncompetitive I = binds E or ES and inhibits reaction… does not reduce E + S affinity
neg allosteric eff = reduces E + S affinity

55
Q

what is the shortcut michaelis-menten equation for uncompetitive inhibition?

A

v0 = VmS / [Km + S (1+I/Ki)]

56
Q

irreversible inhibition most closely resembles which kind of reversible inhibition?

A

noncompetitive

Km is same, Vm is decreased (taking E out)

Biochem 1 (WPH) (15 decks)

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