In oxygenated hemoglobin, pKa = 6.6 for the histidines at position 146 on the -c
ID: 195053 • Letter: I
Question
In oxygenated hemoglobin, pKa = 6.6 for the histidines at position 146 on the -chain. In deoxygenated hemoglobin, the pKa of these residues is 8.2. How can this piece of information be correlated with the Bohr effect? 4. You are studying with a friend who is in the process of describing the Bohr effect. She tells you that, in the lungs, hemoglobin binds oxygen and releases hydrogen ion; as a result, the pH increases. She goes on to say that, in actively metabolizing muscle tissue, hemoglobin releases oxygen and binds hydrogen ion and, as a result, the pH decreases. Do you agree with her reasoning? Why or why not? Hemoglobin extracted from red blood cells has a much greater affinity for oxygen than hemoglobin within a RBC. How do you account for this difference in affinity?Explanation / Answer
Answer 4: In oxygenated conditions, more charges in histidine results in hydrogen binding to it in more stable manner. oxygen binding causes conformational changes from T to R as a result of electrostatic disruption holding hydrogen atoms in its place, thus reducing pKr. However, in deoxygenated conditions, excess of electrostaticity lowers the energy around histidine, resulting in more acidity that in turn stabilizes the change in state upon conformational change to R state.
Answer 5: The pH of the tissue is much lower compared to that of lungs which results in blood releasing more oxygen creating haemoglobin in its t-state. When the blood returns back to the lungs higher pH there will resulting in blood attracting for oxygen for transport. However, compared to haemoglobin, myoglobin holds onto its oxygen and is generally not influenced by the Bohr effect. On average, the haemoglobin can release oxygen approximately nine times higher than myoglobin. In actively metabolising muscle tissue, the oxygen transfer per red blood cell would increase along with rise in the level of carbon dioxide resulting in lower pH in the tissues.
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