Enzyme Action

1
Enzyme Action
Enzymes proteins with catalytic
function possess 1O, 2O, 3O and 4O
structure perform a variety of
reactions e.g., hydrolysis, hydroxylation,
oxidation, reduction, transfer of groups
increase the rate of reaction (up to
1017-fold)
2
Enzyme Action
Three dimensional structure of an enzyme
3
Enzyme Action
Catalytic Triad
Catalytic Triad Chymotrypsin
Acetylcholine Esterase
4
Chemical Mechanism of Enzyme Action
5
Michaelis Menten Kinetics and Enzyme Inhibition
Michaelis-Menten Equation
Michaelis-Menten Equation in the presence of a
competitive inhibitor
What happens at low S in the absence of I? What
happens at high S in the absence of I? What
happens at low S in the presence of I? What
happens at high S in the presence of I?
6
Reaction Mechanisms
Theory of Reaction Rates
A B ? C D
7
Reaction Mechanisms
Theory of Reaction Rates
H2CCH2 HCl ? H3C-CH2Cl
8
Reaction Mechanisms
Collision Theory

• Arrhenius Equation
• Rate PZe(Ea/RT)

• Conc. Of Reactants (Z)
• Temperature (T)
• Activation Energy (EA)
• Probability Factor (P)

9
Reaction Mechanisms
Theory of Reaction Rates

• Arrhenius Equation
• Rate PZe(Ea/RT)

pH 5, halflife 300 yrs
pH 5, halflife 25 days
pH 5, halflife 25 minutes
H
10
Reaction Mechanisms
Application of Reaction Rate Theory
Rank the following molecules according to their
ability to hydrolyze faster in water at pH 6.0.
Use 1 for fastest and 3 for slowest rate of
hydrolysis.
11
Reaction Mechanisms
Application of Reaction Rate Theory
Rank the following molecules containing
ester/amide group according to their ability to
hydrolyze in water at pH 8.0. Use 1 for fastest
rate and 3 for slowest rate of hydrolysis.
12
Reaction Mechanisms
Theory of Reaction Rates

• Enzymes!
• powerful catalysts

85 yrs
_
_
0.01 s
Another example, catalase 2H2O2 ? 2H2O O2 EA
18 kcal/mol in absence 2 kcal/mol in
presence rate increase of 1011 -fold
13
Reaction Mechanisms
Reaction Rates
Consider reactions A) and B). Circle the reaction
that has a longer half-life?