Enzyme substrate regulation levels (5) exam 3 EXSC401.txt
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Enzyme levels of regulation
- 1. *Substrate supply: when high amts of substrate, LESS likely it will UNBIND b/c of diffusion
- 2. *Product Inhibition: When Lots of product surrounding enzyme, LESS likely it will allow for more product to form…may encourage the reverse reaction to favor E+S vs E+P. Also product may inhibit Substrate from binding, via competitive inhibition.
- 3. Allosteric regulation (ie PFK enzyme): utilized in order to regulate speed of reaction occurring, helps to regulate HEAT and Radical Production!
- 4. Covalent modification (ie phosphorylation/dephos)
- 5. Genetic regulation (ie phos of TFs via INcrease in activity of SF pathways)
- *every enzyme subject to these two types of regulation
Example of a enzyme+substrate
- Hexokinase(enzyme) + glucose and ATP(substrate) (E + S) -> binding of substrates to enzyme (E . S)
- Hexokinase bound to product (Glucose-6-phosphate and ADP) (E . P) -> Hexokinase + G-6-P + ADP (E + P)
- Hexokinase has a
Km and 1/2Vmax
- When the substrate concentration  does not have to be high in order to get to 1/2Vmax: LoW Km
- For example, hexokinase moving in the forward reaction does not require high amounts of glucose in order to get to G-6-P: has LOW Km for the substrate
- Hexokinase + product going backwards to glucose from G-6-P is unlikely, reverse reaction is not favored because there is rarely a buildup of G-6-P, since it is beign used steadily for other pathways: High Km for the product!
PFK enzyme and allosteric regulation
- Allosteric regulation: By CHANGING the SHAPE of the enzyme, can CHANGE the Binding constant to INCREASE the LIKELIHOOD for Binding
- AMP with PFK: AMP presence CHANGES the BINDING AFFINITY for the substrate to bind to PFK, Increasing its ability to bind to the substrate (F-6-P and ATP). This gives PFK a LOWER Km
- Decreasing affinity for substrate to PFK: ATP presence REDUCES Binding Affinity for substrate to bind PFK. In this case, PFK is a HIGH Km enzyme!
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