23 bisphosphoglycerate an allosteric effector of

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2,3-bisphosphoglycerate: an allosteric effector of hemoglobin Observation: highly purified (“stripped”) Hb has higher oxygen affinity than Hb in whole blood Led Joseph Barcroft to hypothesize that blood contains something other than CO 2 to affect O 2 binding to Hb This compound is 2,3-BPG: binds with higher affinity to deoxygenated Hb than oxygenated Hb (in lungs) 28
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2,3-BPG Since 2,3-BPG binds at a site distant from the Fe where oxygen binds, it is called an allosteric effector Allosterically promotes release of oxygen in hypoxic tissues 29
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Pure/stripped Hb has higher O 2 affinity than whole blood The presence of BPG decreases Hb’s affinity for O 2 by keeping it in the deoxy conformation 30
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Key concepts: Summary of allosteric effects Oxygen (O 2 ) binds the oxygen-bound state of hemoglobin (oxyhemoglobin) Protons (H + ) bind to the oxygen-unbound state of hemoglobin (deoxyhemoglobin) 2,3-BPG binds with higher affinity to the oxygen-unbound state of Hb (deoxyhemoglobin) – Allosterically promotes release of other O 2 molecules 31
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Sickle Cell anemia Hypothesized in 1945 to result from mutant hemoglobin protein (Linus Pauling) The first inherited disease to be linked with mutation at the amino acid level Hemoglobin proteins aggregate to form long fibers within RBCs Brittle RBCs adopt an elongated “sickle” shape and lose pliability in capillaries This protects against malaria More details here: 32
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1. Which of the following is true regarding the ability of Hb to bind oxygen? A. CO 2 promotes the release of oxygen B. H + and BPG stabilize the deoxy form of Hb. C. A single amino acid change in Hb can cause sickle cell anemia D. All the above are true. 33
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2. During vigorous exercise, the pH of blood passing through skeletal muscle decreases. How does this decrease affect the behavior of hemoglobin? A. It increases O 2 binding to hemoglobin, because it increases the binding of BPG. B. It increases O 2 binding to hemoglobin, because it decreases the binding of BPG. C. It decreases O 2 binding to hemoglobin, because it increases the binding of BPG. D. It decreases O 2 binding to hemoglobin, because it decreases the binding of BPG. 34
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  • Spring '08
  • Huxford
  • Chemistry, Hemoglobin

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