Lecture 2: Enzyme Catalysis

Question 1

Substrate Recognition by Enzymes

Answer 1

-complementary Interactions between substrate and enzyme
-involves induced fit
-Binding (site is a small region)

-similar factors apply to inhibitors and drugs

Question 2

Substate x enzyme Interactions

Answer 2

-highly complementary
-hydrophobic to hydrophobic
-H bonding
-Coulombic interactions

Question 3

Induced fit

Answer 3

-conformational change in enzyme for substrate binding (free vs bound)
-optimal recognition of substrates
-brings in important residues

Question 4

Enzyme inhibition

Answer 4

disruption of catalytic function

Question 5

Catalytic Function

Answer 5

E+S <-k1+2-> E-S –k3-> E+P
+I +I
E-I <———> E-S-I

Question 6

v0

Answer 6

-initial velocity
-measured with constant [E]

Question 7

Lineweaver Burk Plot

Answer 7

1/v0 =1/Vmax + Km/Vmax
-inverse
-straight line

Question 8

Enzyme Inhibitior Types

Answer 8

competitive, mixed (noncompetitive), uncompetitive

Question 9

Competitive inhibition

Answer 9

-interferes with active site
-binds only free E
-V max same
-KM different
-graph slope flatter than regular rate

Question 10

Mixed Inhibition

Answer 10

-competitive and uncompetitive inhibitors
-binds E and E-S complex
-completes catalytic function
-same effect as using less enzyme
-Vmax changes if EI and ESI equilibrium smae

Question 11

Uncompetitive inhbition

Answer 11

-changes shape of enzyme
-Vmax and KM decrease
-binds only E-S complex

Question 12

Which choice best describes
competitive binding between the enzyme
substrate, S, and inhibitor, I?

Answer 12

All of the above
-I binds active site
-I binding site partially overlaps with active site
-I induces change that prevents S bonding

Question 13

Apparent Vmax and Km

Answer 13

-change by (1+[I]/KI)

Question 14

KI

Answer 14

=[E][I]/[E x I]

Question 15

Apparent catalytic constants due to COMPETITIVE inhibition

Answer 15

Km= Km(1+ [I]/K1)

Question 16

Apparent catalytic constants due to NONCOMPETITIVE inhibition

Answer 16

Vmax= Vmax / (1+ [I]/KI)

Question 17

Apparent catalytic constants due to UNCOMPETITIVE inhibition

Answer 17

Km= Km/(1+ [I]/K1)
Vmax= Vmax / (1+ [I]/KI)

Question 18

Competitive inhibitor

Answer 18

-binds only free E
-CHANGE Km

Question 19

non-competitive (mixed) inhibitor

Answer 19

-binds free E and ES complex equally
-CHANGE Vmax

Question 20

uncompetitive inhibitor

Answer 20

-only binds ES complex
-change both

Question 21

2 substrate reactions

Answer 21

E + A <–> EA + B –> E + P + Q
+I1 +I2
EI1 EAI2

Question 22

Inhibition of 2 substrate reactions

Answer 22

-inhibitors of multiple-substrate enzymes bind E or EA

Question 23

Inhibitor binds EI1

Answer 23

competitive against A

Question 24

Inhibitor binds EAI2

Answer 24

competitive against B

Question 25

KI is what type of parameter?

Answer 25

Analogous to KD

Question 26

Uncompetitive inhibitors of an enzyme bind to ES, but not E, so that measuring the catalytic activity with this type of inhibitor

Answer 26

gives both an apparent KM and apparent Vmax

Question 27

kcat is what type of parameter?

Answer 27

Kinetic rate constant INDEPENDENT of enzyme or substrate concentration

Question 28

Alcohol dehydrogenase

Answer 28

-dimer -ethanol --> acetaldehyde -NADH, Zn cofactors

Question 29

linweaver burk x-intercept

Answer 29

-1/Km

Question 30

lineweaver y-intercept

Answer 30

1/Vmax

Question 31

lineweaver slope

Answer 31

Km/Vmax

Question 32

low KM

Answer 32

high affinity