2,3-diphosphoglycerate (DPG) is formed from the glycolytic intermediate 1,3-diphosphoglycerate, by the action of a mutase enzyme (Figure 3.05). It in turn is broken down to 3-phosphoglycerate by a phosphatase enzyme. DPG stabilizes the deoxyconformation of hemoglobin A (adult hemoglobin). This makes it more difficult for oxygen to bind, raising the P50 value.
Hemoglobin F, or fetal hemoglobin, binds little or no DPG, so does not effect the P50 value (Table 3.07).
Increasing blood pH, as during maternal alkalosis, increases the synthesis of DPG, raising DPG concentration, and the P50 value. A decreased hemoglobin-oxygen saturation also increases pH, due to the increased buffering capacity of the hemoglobin. This also elevates DPG synthesis, raising the P50 value.
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