2.3- Bisphosphoglycerate synthesis

The [ATP] / [ADP] ratio in an actively respiring yeast cell is about 10. What would be the intracellular [3-phosphoglycerate] / [1,3-bisphospho-glycerate] ratio have to be to make the phospho-glycerate kinase reaction (Fig. 9-7, reaction 7) proceed toward 1,3-bisphosphoglycerate synthesis at 25°C, pH 7 ... 

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

The formation of 1,3-bisphosphoglycerate involves the synthesis of a high-energy phosphate bond as the aldehyde of glyceraldehyde 3-phosphate is oxidized to a carboxylic acid and then phosphorylated by reaction with inorganic phosphate. 

A requirement for all fermentations is the existence of a mechanism for coupling ATP synthesis to the fermentation reactions. In the lactic acid and ethanol fermentations this coupling mechanism consists of the formation of the intermediate 1,3-bisphosphoglycerate by the glyceraldehyde 3-phosphate dehydrogenase (Fig. 10-3, step a). This intermediate contains parts of both the products ATP and lactate or ethanol. 

This requires the generation of six separate molecules of ribulose bisphosphate from ribulose phosphate, at the cost of one ATP each. Furthermore, two molecules of 1,3-bisphosphoglycerate must be made from the two 3-phosphoglycerates that are the initial product of each C02 fixation reaction. Conversion of each 1,3-bisphospho-glycerate requires an NADPH as well therefore, two NADPH equivalents are consumed for each C02 fixed. Another way of saying this is that carbon is reduced from an oxidation number of -4 in C02 to an oxidation number of zero in carbohydrate (CH20). Therefore, synthesis of one mole of glucose requires the input of 18 ATPs and 12 NADPHs. 

A separate enzyme then transfers the phospho group from the 1 position of 1,3-bisphosphoglycerate to ADP to form ATP and 3-phosphoglycerate (step d). The overall sequence of Fig. 15-6 is the synthesis of one mole of ATP coupled to the oxidation of an aldehyde... 

Bisphosphoglycerate is also responsible for the apparent change in hemoglobin (increased oxygen affinity) when blood is stored in an acid-citrate-dextrose medium. Under these conditions, glycolysis stops and the synthesis of BPG stops. However, the degradation of BPG continues, with a resultant drop in BPG concentration. The situation cannot be reversed by... 

For reasons similar to those discussed for ATP (Section 14.1.4), 1,3-bisphosphoglycerate has a high phosphoryl transfer potential. Thus, the cleavage of 1,3-BPG can be coupled to the synthesis of ATP. 

Figure 14.24 NAD, as the coenzyme in glyceraldehyde-3-phosphate dehydrogenase (GAPDH), is used to oxidize glyceraldehyde-3-phosphate (GAP) to 1,3-bisphosphoglycerate during the degradation of glucose in glycolysis. One of the ways that NADH can be reoxidized to NAD is by the electron transport chain in mitochondria, where, under aerobic conditions, rearomatization of NADH helps to drive ATP synthesis.

Bisphosphoglycerate 03P0CH2CHC02P03 IA phosphate is transferred from the carboxyl group to ADP, resulting in synthesis of an ATP and yielding 3-phosphoglycerate. 

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