Regulation of Glycolysis
REGULATED STEPS IN GLYCOLYSIS
Hexokinase: first step in glycolysis
- Phosphorylates glucose
- Consumes ATP
- Traps glucose within cell
- Muscle: inhibited by glucose 6-P
- Liver: glucokinase isozyme
Phosphofructokinase: committed step
- Most important control element
- First reaction unique to glycolysis
- Phosphorylates fructose 6-P to form fructose 1,6-BP
- Consumes ATP
- Activated by AMP and fructose 2,6-BP (more important in liver)
- Inhibited by ATP, citrate and low pH (muscle)
Pyruvate kinase: last step in glycolysis
- Dephosphorylates phosphenol pyruvate to form pyruvate
- Generates ATP
- Activated by fructose 1,6-bisphosphate and AMP
- Inhibited by: ATP, alanine & Acetyl CoA
MAJOR REGULATION SITES IN GLYCOLYSIS
Muscle
- Requires energy for contraction
- ATP: AMP ratio determines whether glycolysis should move forward
- When ratio is low: glycolysis activated
- 2 ADP combine to form 1 ATP and 1 AMP (free ADP does not persist)
Liver
- Uses molecules from glycolysis to start biosynthetic/metabolic reactions
- High glucose levels: liver stores glucose as glycogen
- Low glucose levels: liver releases glucose
- Liver isozymes allow glucose to be prioritized for brain & muscles