U01.01.096 Glycolysis regulation

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Learning Objectives

  • Summarize the net yield of aerobic glycolysis.
  • Identify the ATP-consuming vs. ATP-producing steps.
  • Master the allosteric regulators of the rate-limiting enzyme, PFK-1.

1. Net Glycolysis Equation

Occurring in the cytoplasm, glycolysis converts one molecule of glucose into two molecules of pyruvate, generating energy and reducing equivalents.

Glucose + 2 Pi + 2 ADP + 2 NAD+ → 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O

2. Key Regulatory Enzymes

Regulation occurs at irreversible steps to ensure that energy production meets the cell’s metabolic demands.

Step Type Enzyme Regulators
ATP Consuming
(Investment)		 Hexokinase / Glucokinase (-) Glucose-6-P (Hexokinase)
(-) Fructose-6-P (Glucokinase)
PFK-1 (Rate-Limiting) (+) AMP, Fructose-2,6-BP
(-) ATP, Citrate
ATP Producing
(Payoff)		 Phosphoglycerate kinase Substrate-level phosphorylation
Pyruvate kinase (+) Fructose-1,6-BP (Feed-forward)
(-) ATP, Alanine, Glucagon, Epinephrine

Biochemical Correlation: Fructose-2,6-Bisphosphate

F-2,6-BP is the most potent activator of PFK-1. Its levels are regulated by the bifunctional enzyme PFK-2/FBPase-2. In the well-fed state, Insulin increases F-2,6-BP to stimulate glycolysis. In the fasting state, Glucagon decreases it to favor gluconeogenesis.

Activity

Clinical Correlate: Pyruvate Kinase Deficiency

A deficiency in Pyruvate Kinase is the second most common cause of enzyme-deficient hemolytic anemia (after G6PD). Without enough ATP from glycolysis, RBCs cannot maintain their Na+/K+ ATPase pumps, leading to rigid cells, swelling, and hemolysis in the spleen.

 

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