ENZYMES
Catalysis can be described formally in terms of
a stabilization of the transition state through
tight binding to the catalyst.
—William P. Jencks, article in Advances in
Enzymology, 1975
1
Schematic figure of (a) enzyme plus substrate and (b) enzyme
plus substrate plus cofactor
2
Some Inorganic Elements That Serve as Cofactors for
Enzymes
3
Some Coenzymes That Serve as Transient Carriers of
Specific Atoms or Functional Groups
4
International Classification of Enzymes
5
Binding of a substrate to an enzyme at the active site
6
Enzymes Affect Reaction Rates, Not
Equilibriaion
7
Some Rate Enhancements Produced by
Enzymes
8
Weak Interactions between Enzyme and Substrate
Are Optimized in the Transition State (Complementary
shapes of a substrate and its binding site on an
enzyme)
9
An imaginary enzyme (stickase) designed to catalyze
breakage of a metal stick.
10
Specific Catalytic Groups Contribute to Catalysis
• General Acid-Base Catalysis
• Covalent Catalysis
• Metal Ion Catalysis
11
Specific Catalytic Groups Contribute to Catalysis
(General Acid-Base Catalysis and Covalent
Catalysis )
12
Specific Catalytic Groups Contribute to Catalysis
(General Acid-Base Catalysis and Metal Ion
Catalysis)
13
Enzyme Kinetics as an Approach to Understanding
Mechanism
Effect
of
substrate
concentration on the initial
velocity of an enzymecatalyzed reaction.
14
Effect of substrate concentration on the initial velocity of an
enzyme-catalyzed reaction (Michaelis-Menten equation)
15
Km for Some Enzymes and Substrates
16
Transformations of
the MichaelisMenten
Equation: The
Double-Reciprocal
Plot
17
Transformations of the Michaelis-Menten
Equation: The Double-Reciprocal Plot
18
Enzymes Are Subject to Reversible
or reversible Inhibition (Competitive)
19
Enzymes Are Subject to Reversible
or reversible Inhibition (Competitive)
20
Enzymes Are Subject to Reversible
or reversible Inhibition (Competitive)
21
Enzymes Are Subject to Reversible
or reversible Inhibition (Uncompetitve)
22
Enzymes Are Subject to Reversible
or reversible Inhibition (Uncompetitve)
23
Enzymes Are Subject to Reversible
or reversible Inhibition (mixed inhibitor)
24
Enzymes Are Subject to Reversible
or reversible Inhibition (Mixed inhibitor)
25
Irreversible inhibition (Reaction of chymotrypsin with
diisopropylfluorophosphate (DIFP) irreversibly
inhibits the enzyme)
26
The pH-activity profiles of two enzymes (Enzyme
Activity Depends on pH)
27
Structure of chymotrypsin
28
Structure of
chymotrypsin
29
Structure of
chymotrypsin
30
31
In Many Pathways
a Regulated Step Is
Catalyzed
by an Allosteric
Enzyme
32
Substrate-activity curves for representative allosteric
enzymes. The sigmoid curve of a homotropic enzyme, in
which the substrate also serves as a positive (stimulatory)
modulator, or activator.
33
Substrate-activity curves for representative allosteric
enzymes. The effects of a positive modulator (+)
and a negative modulator () on an allosteric enzyme in which
K0.5 is altered without a change in Vmax
34
Phosphoryl Groups
Affect the Structure
and
Catalytic Activity of
Proteins
35