Phosphoenolpyruvate Carboxykinase (PEPCK)

PEPCK is an enzyme of gluconeogenesis. It catalyzes conversion of the 4-carbon compound, oxaloacetate, to phosphoenolpyruvate (PEP), releasing CO 2. The reaction requires energy input from GTP and produces GDP.

> Oxaloacetate + GTP <=> PEP + CO 2 + GDP

For PEPCK to function in gluconeogenesis, oxaloacetate produced in the pyruvate carboxylase reaction in the mitochondria, must be transported to the cytoplasm. PEPCK is not under any known allosteric control. Activity of the enzyme is regulated by hormonal control of its transcription. Glucagon stimulates transcription of the structural gene for PEPCK. Insulin inhibits transcription of the enzyme. By inhibiting PEPCK gene transcription, insulin tends to depress gluconeogenesis rates.

See also: Enzymes of Gluconeogenesis, Enzymes of Glycolysis, Pyruvate Carboxylase; Pyruvate Kinase

INTERNET LINKS:

> 1. RasMol Image of PEPCK (slow)

> 2. Glycolysis/Gluconeogenesis