Rate Limiting Steps

• what does adenylate kinase do?

  Cataylyses the conversion of ADP to ATP and AMP
• adenylate kinase produces required ATP, but also produces AMP which alters energy charge and causes increases in catabolic processes
• ATP > ADP >> AMP
• Key enzymes are sensitive to the concentration of ADP and especially AMP
• Key enzymes are not sensitive to ATP
• Normally, only one or two enzymes in a pathway regulate the flow
• What are the properties of RLS?

  Irreversible and saturated with substrate
• How to regulate the flux?

  1. Make the enzyme go faster or slower
  2. Turn the enzyme on/off, or make it work the other way
  3. Increase/decrease the expression of the enzyme
• PFK does not like high concentrations of ATP
• When AMP binds, it changes the way that PFK responds to ATP
• Citrate also binds to PFK allosterically to inhibit its activity
• What binds to PFK to enhance its activity?

  AMP
• What binds to PFK to inhibit its activity?

  Citrate
• G6P inhibits hexokinase as a negative feedback loop to prevent excessive trapping and ATP wastage
•  glucose isn't trapped if G6P isn't being used
• PDH phosphatase is activated by insulin
• PDH kinase is activated by the presence of acetyl CoA
• PDH activity is a balance between phosphatase and kinase activity
• Futile Cycle

  When opposing anabolic and catabolic pathways occur at the same time