Lecture 2: Enzyme Catalysis Flashcards
Substrate Recognition by Enzymes
-complementary Interactions between substrate and enzyme
-involves induced fit
-Binding (site is a small region)
-similar factors apply to inhibitors and drugs
Substate x enzyme Interactions
-highly complementary
-hydrophobic to hydrophobic
-H bonding
-Coulombic interactions
Induced fit
-conformational change in enzyme for substrate binding (free vs bound)
-optimal recognition of substrates
-brings in important residues
Enzyme inhibition
disruption of catalytic function
Catalytic Function
E+S <-k1+2-> E-S –k3-> E+P
+I +I
E-I <———> E-S-I
v0
-initial velocity
-measured with constant [E]
Lineweaver Burk Plot
1/v0 =1/Vmax + Km/Vmax
-inverse
-straight line
Enzyme Inhibitior Types
competitive, mixed (noncompetitive), uncompetitive
Competitive inhibition
-interferes with active site
-binds only free E
-V max same
-KM different
-graph slope flatter than regular rate
Mixed Inhibition
-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
Uncompetitive inhbition
-changes shape of enzyme
-Vmax and KM decrease
-binds only E-S complex
Which choice best describes
competitive binding between the enzyme
substrate, S, and inhibitor, I?
All of the above
-I binds active site
-I binding site partially overlaps with active site
-I induces change that prevents S bonding
Apparent Vmax and Km
-change by (1+[I]/KI)
KI
=[E][I]/[E x I]
Apparent catalytic constants due to COMPETITIVE inhibition
Km= Km(1+ [I]/K1)
Apparent catalytic constants due to NONCOMPETITIVE inhibition
Vmax= Vmax / (1+ [I]/KI)
Apparent catalytic constants due to UNCOMPETITIVE inhibition
Km= Km/(1+ [I]/K1)
Vmax= Vmax / (1+ [I]/KI)
Competitive inhibitor
-binds only free E
-CHANGE Km
non-competitive (mixed) inhibitor
-binds free E and ES complex equally
-CHANGE Vmax
uncompetitive inhibitor
-only binds ES complex
-change both
2 substrate reactions
E + A <–> EA + B –> E + P + Q
+I1 +I2
EI1 EAI2
Inhibition of 2 substrate reactions
-inhibitors of multiple-substrate enzymes bind E or EA
Inhibitor binds EI1
competitive against A
Inhibitor binds EAI2
competitive against B
KI is what type of parameter?
Analogous to KD
Uncompetitive inhibitors of an enzyme bind to ES, but not E, so that measuring the catalytic activity with this
type of inhibitor
gives both an apparent KM and apparent Vmax
kcat is what type of parameter?
Kinetic rate constant INDEPENDENT of enzyme or substrate concentration
Alcohol dehydrogenase
-dimer
-ethanol –> acetaldehyde
-NADH, Zn cofactors
linweaver burk x-intercept
-1/Km
lineweaver y-intercept
1/Vmax
lineweaver slope
Km/Vmax
low KM
high affinity
