Enzymes 3 - inhibition & regulation Spencer

Question 1

T/F covalent interactions bind reversible inhibitors to enzymes

Answer 1

false - non-covalent interactions

Question 2

how does reversible inhibition alter michelis-menten kinetics?

Answer 2

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

Question 3

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

Answer 3

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

Question 4

how does competitive inhibition change the michelis-menten plot?

Answer 4

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

Question 5

how does competitive inhibition change the lineweaver-burke plot?

Answer 5

same Vm so same y-intercept

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

Question 6

how does competitive inhibition change catalytic efficiency?

Answer 6

decreases it

higher Km so kcat/Km is lower

Question 7

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

Answer 7

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

where Ki = dissociation constant for EI

Question 8

how does competitive inhibition work?

Answer 8

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

Question 9

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

Answer 9

true

Question 10

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

Answer 10

transition state analogs - bind more tightly to enzyme

Question 11

what kind of reversible inhibitors bind to free enzyme only

Answer 11

competitive

Question 12

what kind or reversible inhibitors bind to the ES complex only

Answer 12

uncompetitive

Question 13

what kind of reversible inhibitors bind to E or ES complex

Answer 13

noncompetitive

Question 14

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

Answer 14

uncompetitive

Question 15

what is the michelis-menten equation for uncompetitive inhibition?

Answer 15

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

Question 16

how does uncompetitive inhibition alter the michelis-menten plot?

Answer 16

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

Question 17

how does uncompetitive inhibition alter the lineweaver-burke plot?

Answer 17

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

Question 18

how does uncompetitive inhibition alter catalytic efficiency?

Answer 18

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

Question 19

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

Answer 19

uncompetitive

Question 20

how do uncompetitive inhibitors work?

Answer 20

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

Question 21

how does noncompetitive inhibition work?

Answer 21

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

Question 22

how does noncompetitive inhibition alter the michelis-menten plot?

Answer 22

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

Question 23

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

Answer 23

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

Question 24

how does noncompetitive inhibition alter the lineweaver-burke plot?

Answer 24

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

Question 25

how does noncompetitive inhibition affect catalytic efficiency?

Answer 25

decreases it kcat down Km same kcat/Km down

Question 26

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

Answer 26

noncompetitive | only affects catalytic mechanism

Question 27

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

Answer 27

competitive

Question 28

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

Answer 28

``` uncompetitive = no early gap, lower Km noncompetitive = early gap, same Km ```

Question 29

conceptually, why does uncompetitive inhibition lower Km?

Answer 29

because [I] effectively takes some

Question 30

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

Answer 30

competitive uncompetitive noncompetitive

Question 31

conceptually, why do uncompetitive inhibitors lower Km?

Answer 31

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

Question 32

conceptually, why do noncompetitive inhibitors not lower Km?

Answer 32

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

Question 33

how does irreversible inhibition work?

Answer 33

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

Question 34

3 categories of irreversible inhibitors

Answer 34

group-specific affinity labels suicide inhibitors

Question 35

how does irreversible inhibition affect Vm and Km?

Answer 35

decrease Vm | no change Km

Question 36

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

Answer 36

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

Question 37

which irreversible inhibitors are substrate analogs?

Answer 37

affinity labels and suicide inhibitors | group-specific reagents do not always bind active site

Question 38

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

Answer 38

true - usually sigmoidal v0 vs [S] relationship

Question 39

what is a homotropic effector

Answer 39

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

Question 40

what is a heterotropic effector

Answer 40

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

Question 41

T/F allosteric enzymes are always oligomers

Answer 41

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

Question 42

how do regulatory proteins work in the case of PKA

Answer 42

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

Question 43

what is reversible covalent modification

Answer 43

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

Question 44

what is proteolytic activation

Answer 44

activating an enzyme by irreversibly cleaving part of the molecule away

Question 45

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

Answer 45

enzyme inhibition and/or control

Question 46

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

Answer 46

true

Question 47

does allosteric regulation involve covalent or non-covalent binding?

Answer 47

non-covalent

Question 48

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

Answer 48

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

Question 49

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

Answer 49

false - phosphatase and kinase only work in one direction each

Question 50

T/F phosphorylation and dephosphorylation are each reversible reactions

Answer 50

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

Question 51

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

Answer 51

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

Question 52

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

Answer 52

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

Question 53

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?

Answer 53

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

Question 54

what is difference between noncompetitive inhibitor and negative allosteric effector?

Answer 54

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

Question 55

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

Answer 55

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

Question 56

irreversible inhibition most closely resembles which kind of reversible inhibition?

Answer 56

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