Bisphosphoglycerate compound also called glycerate23bisphosphate has two important

biological activities.

1. 2,3-bisphosphoglycerate is formed both by phosphoglycerate mutase (transiently) and bisphosphopglycerate mutase. The mechanism of the reaction catalyzed by phosphoglycerate mutase involves formation of 2,3-bisphosphoglycerate via transient phosphorylation of a histidine residue of the ^ ^ enzyme. 2,3BPG can diffuse from phosphoglycerate mutase, however, leaving the enzyme trapped in an unusable state. Cells make excess 2,3BPG (using the 253-BiSphOSphOCjlyCCrcitC

enzyme bisphosphoglycerate mutase) in order to drive

2,3BPG back to phosphoglycerate mutase, so the reaction can go to completion.

2. As Figure 7. shows, 2,3-BPG binds in the cavity between the fi chains of lemoglobin, making electrostatic interactions with positively charged groups surrounding this opening. Comparison of the two hemoglobin conformations shown in Figure 7.12b shows that this opening is much narrower in oxyhemoglobin than in deoxyhemoglobin. In fact, 2,3-BPG cannot be accommodated in the oxy form. The higher the 2,3-BPG content in red blood cells, the more stable the deoxy structure will be. The decrease in O2 affinity by hemoglobin is explained by stabilization of the deoxy structure. Increased 2,3-BPG levels are also found in the blood of smokers, who because of the carbon monoxide in smoke also suffer from limitation in oxygen supply.

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