MB - Metabolic Control via Enzyme Regulation I Flashcards
What is a metabolic pathway?
The enzymatic route that a metabolite molecule takes
What are the rate-limiting steps of a metabolic pathway?
- Slowest reaction in the pathway
- Usually the first unique enzyme in a pathway
What are 3 ways to identify the RLS?
1) Measure Vmax for enzymes in a pathway
* Lowest- RLS
2) Compare Keq and mass action ratios
* MAR is usually 100-1000 times < Keq for RLS
3) Test if step is at crossover point
What 2 enzymes are of regulatory importance in glycolysis?
- Hexokinase
- Phosphofructokinase-1
What is the need for metabolic control? (3)
- Ensures a given metabolic pathway is active when its product is needed
- Ensures competing pathways aren’t simultaneously active
- Ensures co-ordinated activity in multiple related pathways
What are the 3 types of enzyme regulation?
1) Intrinsic control by metabolites- Allosterism/Inhibitors
2) Fast extrinsic control via hormones- Covalent modification (phosphorylation)
3) Slow extrinsic control via hormones- Gene expression
What is product inhibition?
The product acts to inhibit the enzyme making it
* e.g G-6-P inhibits its own production in glycolysis (Hexokinase)
What is allosterism?
The interaction between molecules influences the binding of another
* e.g F-2,6-P2 increases PFK-1 activity
* e.g F-2,6-P2 inhibits FBPase-1 activity
What do hormones alter in relation to enzymes?
Activity of enzymes
* Rapid, via phosphorylation
* Short-lived effect
Number of enzymes
* Slow, via gene expression changes
* Longer-lived effect
How does phosphorylation alter the activity of enzymes?
Phosphorylation –> Conformational change
–> Activation or Inactivation