Food Chemistry and Fish in Nutrition ( 2+1)

6.4.1.1. Conversion of Pyruvate into Phosphoenolpyruvate

Pyruvate carboxylase, present in mitochondria, converts pyruvate to oxaloacetate in the presence of ATP, the B vitamin biotin, and CO₂ . The function of the biotin is to bind CO₂ from bicarbonate onto the enzyme prior to the addition of the CO₂ to pyruvate.

A second enzyme, phosphoenolpyruate carboxykinase, catalyzes the conversion of oxaloacetate to phosphoenolpyruvate. High energy phosphate in the form of GTP or ITP is required in this reaction, and CO₂ is liberated.

Thus, with the help of these two enzymes catalyzing endergonic transformations and lactate dehydrogenase, lactate can be converted to phosphoenolpyruvate, overcoming the energy barrier between pyruvate and phosphoenolpyruvate.