Mature red blood cells lack both nuclei and mitochondria. Without mitochondria they cannot respire aerobically; the very cells that carry oxygen are the only cells in the body that cannot use it! Red blood cells, therefore, must obtain energy through the anaerobic respiration of glucose. At a certain point in the glycolytic pathway, a "side reaction" occurs in the red blood cells that results in a unique product—2,3-diphosphoglyceric acid (2,3-DPG).
The enzyme that produces 2,3-DPG is inhibited by oxy-hemoglobin. When the oxyhemoglobin concentration is decreased, therefore, the production of 2,3-DPG is increased. This increase in 2,3-DPG production can occur when the total hemoglobin concentration is low (in anemia) or when the Po2 is low (at a high altitude, for example). The bonding of 2,3-DPG with deoxyhemoglobin makes the deoxyhemo-globin more stable. Therefore, a higher proportion of the oxyhemoglobin will be converted to deoxyhemoglobin by the unloading of its oxygen. An increased concentration of 2,3-DPG in red blood cells thus increases oxygen unloading (table 16.9) and shifts the oxyhemoglobin dissociation curve to the right.
The importance of 2,3-DPG in red blood cells is now recognized in blood banking. Red blood cells that have ^ \ ^ been stored for some time can lose their ability to produce 2,3-DPG as they lose their ability to metabolize glucose. Modern techniques for blood storage, therefore, include the addition of energy substrates for respiration and phosphate sources needed for the production of 2,3-DPG.
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