1,3-Bisphosphoglycerate, from

Bisphosphoglycerate mutase catalyzes formation of 2,3 bisphosphoglycerate from 1,3 bisphosphoglycerate. This reaction is important for maintaining the 3-phosphyglycerate mutase reaction. 

A low PO2 in peripheral tissues promotes the synthesis in erythrocytes of 2,3-bisphosphoglycerate (BPG) from the glycolytic intermediate 1,3-bisphosphoglycerate. 

Figure 6.13 The effect of different concentrations of 2,3-bisphosphoglycerate on the oxyhaemoglobin dissociation curve. The increase in the concentration of BPG from 4 to 5 mmol/L results in an increase in the amount of oxygen released in the capillaries by more than 20%. The concentration of BPG decreases on storage of erythrocytes, so that cells from the blood bank have a higher affinity for oxygen and hence discharge less oxygen in the tissue.

Box 6.1 2,3-Bisphosphoglycerate and the dissociation of oxygen from oxyhaemoglobin in patients and athletes... 

A monomeric enzyme, PGK transfers the acylated phosphoryl group from 1,3- bisphosphoglycerate to ADP, thus forming 3-phosphoglycerate and ATP. The enzyme uses a metal ion as a cofactor, namely Mg2+ [65]. The PGK enzyme from T. bruceihas been overexpressed in E. coli [66]. Human PGK is not... 

The outcome of these coupled reactions, both reversible under cellular conditions, is that the energy released on oxidation of an aldehyde to a carboxylate group is conserved by the coupled formation of ATP from ADP and Pj. The formation of ATP by phosphoryl group transfer from a substrate such as 1,3-bisphosphoglycerate is referred to as a substrate-level phosphorylation, to distinguish this mechanism from respiration-linked phosphorylation. Substrate-level phosphorylations involve soluble enzymes and chemical intermediates (1,3-bisphosphoglycerate in this case). Respiration-linked phosphorylations, on the other hand, involve membrane -bound enzymes and transmembrane gradients of protons (Chapter 19). 

For each molecule of glucose formed from pyruvate, six high-energy phosphate groups are required, four from ATP and two from GTP. In addition, two molecules of NADH are required for the reduction of two molecules of 1,3-bisphosphoglycerate. Clearly, Equation 14-9 is not simply the reverse of the equation for conversion of glucose to pyruvate by glycolysis, which requires only two molecules of ATP ... 

H+, C02 and 2,3-bisphosphoglycerate are allosteric effectors, promoting the release of 02 from hemoglobin. H+ and C02 bind to different parts of the polypeptide chains, while 2,3-bisphosphoglycerate binds in the central cavity between the four subunits. 

Hemoglobin F (HbF) which consists of two a-chains and two y-chains (a2y2) is present in the fetus. HbF binds 2,3-bisphosphoglycerate less strongly than adult hemoglobin (HbA) and thus has a higher affinity for 02 which promotes the transfer of Oz from the maternal to the fetal circulation. 

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