Download survey of biochemistry - School of Chemistry and Biochemistry

SURVEY OF BIOCHEMISTRY
Enzyme Catalysis
1
Enzymatic Catalysis: Recap
• General Properties of Enzymes
– 6 Enzyme Classes
– Substrate Specificity
– Types of Cofactors
• Transition State Diagrams
– Activation Energy
– Reactions vs. Products
– ∆G vs ∆G‡
2
Catalytic Mechanisms:
Learning Goals
• Types of Catalysis
– Acid-Base Catalysis
– Covalent Catalysis
– Metal Ion Catalysis
• Examples
– Lysozyme
– Serine Proteases
3
PRS
• What is a Lewis base?
1. A molecule that
2. A molecule that
3. A molecule that
pair
4. A molecule that
pair
donates H+
donates OHdonates an electron
accepts an electron
4
PRS
• Which of the following is a Schiff base
(imine) group?
1.
3.
2.
4.
Table 1-2
5
Acid-Base Catalysis
• General acid catalysis
H+ transfer from an acid lowers the free
energy of the transition state
6
Base Catalysis
• General base catalysis
H+ is abstracted by a base to lower the free energy
of the transition state
7
Example: RNase A
• Function: Truncate RNA
• Observations
– Isolated RNA intermediates
– Ionizable residues detected
– Chemical derivatization
– Structure determination by x-ray
crystallography
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Example: RNase A
9
Example: RNase A
10
Covalent Catalysis
• Covalent catalysts accelerate rxns by
forming a covalent bond between E and S.
Explain conversion of acetoacetate to acetone on board
Figure 11-11
11
Nucleophiles & Electrophiles
Electron pair donor or
negative charge
Electron-deficient
atoms
12
Metal Ions as Catalysts
CO2 + H2O
HCO3- + H+
Example:
Carbonic
Anhydrase
13
Lysozyme
Lysozyme cleaves polysaccharides via a covalent
reaction mechanism
14
Serine Proteases
Serine proteases involve covalent
catalysis, general base catalysis
and electrostatic interactions
15