2.3- bisphosphoglycerate concentrations

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.

The concentration in the erythrocytes of 2,3-bisphosphoglycerate that influences the dissociation curve of oxyhaemoglobin (Chapter 6). 

Carboxylic acids. Aliphatic carboxylic acids (R—GOOH) are deprotonated at physiological pH (pH 7) and are therefore represented as R—COO. Thus, acetic acid (GHj—COOH) exists as acetate (CH3COO ) at pH 7. A variety of short chain mono-, di-and tricarboxylic acids are important intermediates in metabolism and may be present at low concentrations in all cells either as the acid or as a covalent adduct. Thus, acetate (C2) and malonate (C3) can exist as the key acyl-coenzyme A thioester intermediates acetylGoA and malonylCoA, respectively. Phosphoenolpyruvate (C3), 1,3-bisphosphoglyceric acid (C3) and 3-phosphoglyc,erate (C3) are key metabolic intermediates. 

Figure 2-13. Oxygen saturation curves for myoglobin and adult hemoglobin (HbA). Myoglobin has a hyperbolic saturation curve. HbA has a sigmoidal curve. The HbA curve shifts to the right at lower pH, with higher concentrations of 2,3-bisphosphoglycerate (BPG), or as C02 binds in the tissues. Thus, 02 is released more readily. P50 ( ) is the partial pressure of 02 at which HbA is half-saturated with 02.

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... 

Now we come to an interpretation of these experimental results. The measurements are of limited precision but adequate for a useful analysis. In this analysis we made a point of sequestering ourselves as much as possible from prior available information in order to establish a severe test of the pulse method. In fact, we first assigned random numbers to the chemical species, and then repeated the analysis with the known names of the species. The conclusions were not different and hence for ease of presentation we use the chemical names. We could not detect GAP and 1,3-bisphosphoglycerate. Further, we assumed DHAP and GAP to be in rapidly established equilibrium, which we confirmed by experiment. The ratio of DHAP to GAP was found to be close to the equilibrium constant of the isomerization, 0.045. The equilibrium is way on the side of DHAP, and therefore the concentration of GAP is quite small and not measurable. A number of features of the reaction pathway can be deduced from the experiments with a pulse of G6P. Strong propagation to F6P suggests that this species follows G6P F6P is the first species to respond to the pulse. The pulse of G6P propagates next to DHAP, which follows F6P in the pathway. 

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