Triosephosphate

Triosephosphate refers to any phosphorylated three-carbon sugar phosphate. The two principal triose phosphates in biochemistry are glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP). They are interconvertible by the enzyme triose phosphate isomerase, allowing cellular metabolism to channel carbon between different pathways.

In glycolysis, G3P is the form that directly participates in the main energy-yielding steps. G3P is oxidized and phosphorylated to 1,3-bisphosphoglycerate, generating NADH in the process. This compound is then converted to 3-phosphoglycerate with the production of ATP. The pathway proceeds to pyruvate, and because each glucose molecule yields two G3P molecules, glycolysis provides a net gain of ATP and NADH per glucose (two ATP molecules net and two NADH).

DHAP serves as a metabolic reservoir that can be isomerized to G3P to feed glycolysis. In many tissues, DHAP is also used in other metabolic roles, notably in the glycerol-3-phosphate shuttle, which transfers reducing equivalents from cytosolic NADH into mitochondria for oxidative phosphorylation. DHAP is also a precursor for lipid biosynthesis via glycerol-3-phosphate.

Outside glycolysis, triose phosphates are central in carbon metabolism for photosynthesis and carbohydrate synthesis. In plants and algae, glyceraldehyde-3-phosphate is produced in the Calvin cycle and can be exported from chloroplasts to form sucrose and starch, or used to regenerate ribulose-1,5-bisphosphate. The balance between G3P and DHAP and their partitioning into various biosynthetic routes link energy production with biomass formation.