Enzyme Kinetics
Assumptions made in the derivation of the rate law for enzyme kinetics.
1)
Enzyme concentration is negligible compared to the substrate concentration.
2)
Rate measured is "initial rate " i.e., only a few percent of the reaction is followed
Inhibition of Enzyme Catalysis Uncompetitive Inhibition.
Applying the steady-state approximation to the above scheme, i.e., if the reaction rate is approximately
constant over the time interval concerned then [ES] is also constant:
d EI
dt
0 k3 ES I k 3
Steric inhibition of resonance
Compound
N
Gaq relative to
NH4+ (kJ mol1)
pKasolution
Ggas relative to
NH4+ (kJ mol1)
10.9
10.1
26.4
3.19
6.61
21.8
1.96
7.79
26.0
I
N
II
N
III
Analysis of the solution data
In passing from I II, drop in pKa is explained on
Steric and Inductive Effects.
Analysed using mean CD, CH bond lengths
In an asymmetric potential
energy well.
In a symmetric potential
energy well.
The average CD and CH bond lengths are equal in a symmetric energy well, however, in
an asymmetric potentia
Lifetimes of Reaction Intermediates and Mechanism.
SN1 Reactions.
For many nucleophilic substitutions reactions, the rate does not depend on [Nuc]. Hence,
the activated complex does not contain the nucleophile and is only comprised of SM (+
solvent).
Ar1
Catalysis, Inhibition and Free Energy
If we use transition state theory in which there is a pseudo equilibrium between ground state and
transition state (K ) then we can write the following equations based on the thermodynamic cycle:
KTS K m
K uncat
K cat
Laser Flash Photolysis (and fast kinetics)
Electromagnetic radiation waves propagating through space involving oscillating electric and
magnetic fields at right angles to each other and to the direction of propagation
electromagnetic radiation can be rega
-assisted ionization.
HOAc
TsO
H
H
OAc
Inverted
HOAc
Cl
AcO
+
HOAc
krel = 100 (relative to chlorocyclohexane)
Winstein studies the tosylate solvolysis
AcO
HOAc
TsO
+
+
OAc
HOAc
The cyclopropyl carbinyl acetate product rearranged to the -acetate at an acce