Glyceraldehyde 3-phosphate

Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GADP, GAP or PGAL, is a chemical compound that occurs as an intermediate in several central metabolic pathways of all organisms. It is a phosphate ester of the 3-carbon sugar glyceraldehyde and has chemical formula C3H7O6P.

The CAS number of glyceraldehyde 3-phosphate is 142-10-9 and that of D-glyceraldehyde 3-phosphate (one of the two optical isomers of the compound and the one most often occurring in living organisms) is 591-57-1.

Formation
D-glyceraldehyde 3-phosphate is formed from the following three compounds in reversible reactions:


 * Fructose-1,6-bisphosphate (F1,6BP), catalyzed by aldolase.

The numbering of the carbon atoms indicates the fate of the carbons according to their position in fructose 6-phosphate.


 * Dihydroxyacetone phosphate (DHAP), catalyzed by triose phosphate isomerase.


 * 1,3-bisphosphoglycerate (1,3BPG), catalyzed by glyceraldehyde 3-phosphate dehydrogenase.

As a substrate

 * To produce 1,3-bisphospho-D-glycerate in glycolysis.

D-glyceraldehyde 3-phosphate is also of some importance since this is how glycerol (as DHAP) enters the glycolytic and gluconeogenetic pathways. Furthermore, it is a participant in and a product of the pentose phosphate pathway.

An intermediate in photosynthesis
During plant photosynthesis, two molecules of glycerate 3-phosphate (GP) are produced by the first step of the light-independent reactions when ribulose 1,5-bisphosphate (RuBP) and carbon dioxide are catalysed by the rubisco enzyme. The GP is converted to D-glyceraldehyde 3-phosphate using the energy in ATP and the reducing power of NADPH as part of the Calvin cycle. This returns ADP, phosphate ions Pi, and NADP+ to the light-dependent reactions of photosynthesis for their continued functioning. RuBP is regenerated for the Calvin cycle to continue.

G3P is generally considered the prime end-product of photosynthesis and it can be used as an immediate food nutrient, combined and rearranged to form monosaccharide sugars, such as glucose, which can be transported to other cells, or packaged for storage as insoluble polysaccharides such as starch.

Balance sheet
6 CO2 + 6 RuBP (+ energy from 12 ATP and 12 NADPH) → 12 G3P (3-carbon)

10 G3P (+ energy from 6 ATP) → 6 RuBP (ie starting material regenerated)

2 G3P → glucose (6-carbon).

In tryptophan biosynthesis
Glyceradehyde 3-phosphate occurs as a byproduct in the biosynthesis pathway of tryptophan, an essential amino acid that cannot be produced by the human body.

In thiamine biosynthesis
Glyceraldehyde 3-phosphate occurs as a reactant in the biosynthesis pathway of thiamine (Vitamin B1), another substance that cannot be produced by the human body.