Enzyme Action
1 Enzyme Action
Outline - Chapter 6 in Text
- Competitive vs. Non-competitive Inhibitors
- Models of action
- Effects on observed Reaction Rates
- Other Factors Affecting Enzymes
- Catalytic Mechanisms
- Regulation of Enzymes
2 Competitive Inhibitors
Competitive inhibitors bind to active site of enzyme.
Generally similar in structure to 'desired' substrate.
Examples
- CO competes with O 2 for hemoglobin
- Both diatomic, non-polar molecules
- Both bind to iron site (but CO binds better)
- Malonate competes with Succinate in Krebs cycle
- Succinate: - OOC-CH 2 -CH 2 -COO -
- Malonate: - OOC-CH 2 -COO -
3 Non-competitive Inhibitors
Non-Competitive inhibitors do NOT bind to active site of enzyme.
Generally very different in structure to 'desired' substrate.
Examples
- BPG and pH effects on binding of O 2 with hemoglobin
- H + and BPG both ionic. O 2 non-polar.
- BPG binds to center of hemoglobin. O 2 binds to iron.
- Acetyl-Co ® Citrate
- Inhibited by NADH and ATP
- Very different structures
4 Rates with Competitive Inhibitor
Competitive Inhibitors
- Observed K M changes.
(K M relates to binding of substate to active site)
- V max doesn't change
- Can reduce effects of inhibitor by increasing [S]
- Ex. Give O 2 to patient suffering from CO exposure
5 Rates with Non-Competitive Inhibitor
Non-Competitive Inhibitors
- Observed V max changes.
(Inhibitor causes enzyme to change shape to less active form)
- K M unaffected
(Immediate vicinity of active site little changed)
6 Graphically: Competitive
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7 Graphically: Non-competitive
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8 Allosteric Enzymes
(See text page 131.)
- Complex behavior
- Doesn't match Michaelis-Menton Model
- Generally due to changes in shape of enzyme (induced fit model)
- Typically starts with slower than expected rates
9 Other factors affecting Enzymes
- Cofactors
Typically metals (Fe +2 , Mg +2 , Cu +2 , ...)
- Coenzymes
Typically derived from vitamins
- pH
Can change charge and shape of enzymes
(See Figure 6.20, p. 139)
- Temperature
Rate increases until enzyme denatured
(See Figure 6.19, p. 139)
10 Reaction Mechanisms
- Alcohol Dehydrogenase
See text Figure 6.22, p. 142
- Cymotrypsin
See text Figure 6.21, p. 141
11 Enzyme Regulation
Zymogens (proenzymes)
- Inactive form.
- Covalent modification (bond making/breaking) converts to active form
File translated from TEX by TTH, version 3.02.
On 20 Feb 2002, 16:22.