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Lecture 2
• August 3, 2005
• Lehninger (4th Edition), Chapter 6,
ENZYME KINETICS
LNC Chapter 6
REACTANTS
SUBSTRATESPRODUCTS
kFirst order reactions: A P
kSecond order reactions: A + B P
A + A P
1st order: ln[A] = ln[Ao] - kt or [A] = [Ao] exp(-kt)
2nd order: 1/[A] = 1/[Ao] + kt
time
[A]
time
[A]
1
time
ln [A]
TRANSITION STATE THEORY
A C
B D
A C
B D
A C
B D
A catalyst serves in at least two ways:it binds and aligns the substratesit facilitates the redistribution of electrons (charges)
k1 k2
E + S ES Products k-1
CHAPTER 6
Enzymes and Enzyme Kinetics
Fig. 6-2
Fig. 6-3
Derivation of Michaelis-Mentenequation
• 1. equilibrium assumption: k-1 >> k2
• 2. steady state assumption: d[ES]/dt = 0
• Note: [E] = [E]total – [ES]
Hmmm..??
when [S] >> Km
then
v vmax and vmax = k 2 [E] T
k2 x [E]T x [S]v = ------------------------- Km + [S]
k -1 + k 2 Km =
k 1
d
Km Kd
when
k -1 >> k 2
Fig. 6-11
Fig. 6-12
1 Km 1 1 = x +vo v max [S] v max
y = ax + b
Lineweaver-Burk Plot
Double Reciprocal Plotbox. 6-1
- another definition:
v max
k2 = k cat = ------------ [E] T
TURNOVER NUMBER
molecules of substrate / molecule of enzyme / second
moles of substrate / mole of enzyme / second
Reactions with more than one substrate
(more typical)
Overall reaction:
S1 + S2 P1 + P2
Fig. 6-13
LNC 6-14 a
Lines intersect: ternary complex is formed in the reaction
LNC 6-13 b
This case is also referred to as the Ping-Pongor
double displacement mechanism
LNC 6-14 b
Lines do not intersect: no ternary complex is formed
Enzyme Inhibitors
Fig. 6-15a
Competitive Inhibition
= 1 + [I] / KI
box. 6-2.1
Fig. 6-15b
Uncompetitive Inhibition
’ = 1 + [I] / KI
box. 6-2.2
Fig. 6-15c
Mixed Inhibition
When = ’, then we also speak of noncompetitive inhibition
box 6-2.3
LNC 6-28
FEEDBACK INHIBITION
LNC 6-26
LNC 6-27
ASPARTATE TRANSCARBAMYLASE
LNC 6-29a
LNC 6-29b
LNC 6-29c
Part III
Bioenergetics and MetabolismChapter 13 in LNC
THE CARBON CYCLE
urea
THE NITROGEN CYCLE
Types of Organic Reactions
1) Group transferGlucose + ATP Glu-6-P + ADPH2O + ATP Pi + ADP
2) Oxidation-reduction reactionsEthanol + NAH+ acetaldehyde + NADH + H+
3) Eliminations, isomerizations, rearrangementsaldose ketose
4) reactions involving making or breaking of C-C bondsFru-1,6, bisphosphate dihydroxyacetone-phosphate
+ glyceraldehyde-3phosphate
• End of Lecture 2
• Aug. 3, 2005