3-Phosphoglyceric acid


3-Phosphoglyceric acid is the conjugate acid of glycerate 3-phosphate. The glycerate is a biochemically significant metabolic intermediate in both glycolysis and the Calvin cycle. This anion is often termed as PGA when referring to the Calvin cycle. In the Calvin cycle, 3-phosphoglycerate is the product of the spontaneous scission of an unstable 6-carbon intermediate formed upon CO2 fixation. Thus, two equivalents of 3-phosphoglycerate are produced for each molecule of CO2 that is fixed.

Glycolysis


Calvin cycle

In the light-independent reactions, two 3-phosphoglycerate molecules are synthesized, one of which continues through the Calvin cycle to be regenerated to RuBP and the other is reduced to form one molecule of glyceraldehyde 3-phosphate. This is the first compound formed during the C3 or Calvin cycle. It is a reactive biomolecule that is easily reduced.

Amino acid synthesis

Glycerate 3-phosphate is also a precursor for serine, which, in turn, can create cysteine and glycine through the homocysteine cycle.