13Bisphosphoglycerate

1,3-bisphosphoglycerate, commonly abbreviated as 1,3-BPG or 13-BPG, is a phosphorylated intermediate in glycolysis. It is formed from glyceraldehyde-3-phosphate by the enzyme glyceraldehyde-3-phosphate dehydrogenase in a redox reaction that reduces NAD+ to NADH and incorporates an inorganic phosphate to yield a high-energy acyl phosphate on carbon 1 while preserving a phosphate on carbon 3.

Chemically, it contains phosphate esters at both the C1 and C3 positions of the glycerol backbone. The formation of the molecule couples oxidation of glyceraldehyde-3-phosphate to the generation of a high-energy phosphate bond that can be exploited for ATP production.

The next step in glycolysis is catalyzed by phosphoglycerate kinase, which transfers the high-energy phosphate from C1 to ADP, producing ATP and 3-phosphoglycerate. This reaction provides one molecule of substrate-level ATP per molecule of 1,3-BPG formed, contributing to the overall energy yield of glycolysis.

In addition to its central role in energy metabolism, 1,3-BPG links redox chemistry to energy capture. Cellular concentrations of 1,3-BPG reflect glycolytic flux, and in erythrocytes a related shunt converts 1,3-BPG to 2,3-bisphosphoglycerate (2,3-BPG), a regulator of hemoglobin's oxygen affinity.

1,3-BPG is typically present only transiently in the cytosol during active glycolysis. See also glycolysis, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and 2,3-bisphosphoglycerate.