3Phosphoglycerate

3-Phosphoglycerate, commonly abbreviated 3-PGA, is a phosphorylated three-carbon metabolite that plays a central role in both glycolysis and photosynthetic carbon fixation. It is a glycerate molecule bearing a phosphate ester on the third carbon and exists in solution primarily as a dianionic or monoanionic phosphate form at physiological pH.

In glycolysis, 3-PGA is produced as an intermediate in the latter stages of the pathway. The conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate by phosphoglycerate kinase generates ATP. Subsequently, 3-PGA is converted to 2-phosphoglycerate by phosphoglycerate mutase and then to phosphoenolpyruvate by enolase, continuing toward pyruvate production and further ATP yield.

In photosynthetic organisms, 3-PGA is an early product of carbon fixation. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) catalyzes the carboxylation of ribulose-1,5-bisphosphate to form two molecules of 3-PGA per CO2 fixed. 3-PGA is then reduced to glyceraldehyde-3-phosphate using ATP and NADPH, a step that ultimately supports carbohydrate synthesis and the regeneration of RuBP for ongoing CO2 fixation.

3-PGA is a ubiquitous metabolite found in most organisms, serving as a nexus between energy capture in glycolysis and carbon assimilation in photosynthesis. Its levels and flux are tightly regulated as part of cellular energy balance and carbon economy.