The main precursors of glyceroneogenesis are pyruvate, lactate, glutamine, and alanine. Glyceroneogenesis is also known as the branched pathway of gluconeogenesis because its first few steps are the same.
When pyruvate or lactate is used as the precursor for glycerol 3-phosphate, glyceroneogenesis follows the same pathway as gluconeogenesis until it generates dihydroxyacetone phosphate. Lactate catalyzed by lactate dehydrogenase will form pyruvate at the expense of NAD+. By using one ATP and bicarbonate, pyruvate will be converted to oxaloacetate, catalysed by pyruvate carboxylase. The PEPC-K enzyme will catalyze oxaloacetate to generate phosphoenolpyruvate. This phosphorylation and decarboxylation of oxaloacetate is a significant step in glyceroneogenesis, since it regulates the entire pathway. After the production of phosphoenolpyruvate, gluconeogenesis will continue until dihydroxyacetone phosphate is generated, which produces 2-phosphoglycerate, 3-phosphoglycerate, 1,3-bisphosphoglycerate and glyceraldehyde 3-phosphate as intermediates. When dihydroxyacetone phosphate is produced, glyceroneogenesis will branch off from gluconeogenesis. With the expense of NADH, dihydroxyacetone phosphate will convert to glycerol 3-phosphate, which is the final product of glyceroneogenesis. In addition, triglyceride can be generated by re-esterifying 3 fatty acid chains on glycerol 3-phosphate. Instead of producing fructose 1,6- bisphosphate as gluconeogenesis does, glyceroneogenesis converts dihydroxyacetone phosphate to glycerol 3-phosphate.
Alanine can also be used as a precursor of glyceroneogenesis because alanine can be degraded to pyruvate. Alanine will degrade to pyruvate by transferring its amino group to 2-oxoglutarate with an enzyme called alanine aminotransferase. Alanine aminotransferase cleaves off the amino group from alanine and binds it to 2-oxoglutarate, generating pyruvate from alanine, and glutamate from 2-oxoglutarate. Pyruvate generated from alanine will enter glyceroneogenesis and generate glycerol 3-phosphate.
Glutamate can also enter glyceroneogenesis. Since the key reaction of glyceroneogenesis is the decarboxylation and phosphorylation of oxaloacetate to phosphoenolpyruvate, in theory any biochemical pathway which generates oxaloacetate is related to glyceroneogenesis. For example, glutamate can generate oxaloacetate in 2 steps. Firstly, glutamate can be converted to 2-oxoglutarate with the expense of NAD+ and HO with the help of glutamate dehydrogenase. Secondly, 2-oxoglutarate can enter the tricarboxylic acid cycle to generate oxaloacetate. Therefore, theoretically any metabolites in the TCA cycle or any metabolites generating the metabolites of the TCA cycle can be used as a precursor of glyceroneogenesis, but glutamate is the only precursor confirmed.