Lecture10

Lecture10 - /14/11 Background reading Assignment Segel Berg...

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Lecture 10 10/14/11 Background reading: Outline: ± Hemoglobin as a blood buffer. ± Bohr effect. ± Effect of 2,3-Bisphosphoglycerate on oxygen affinity of hemoglobin. Effect of carbon monoxide on ability of hemoglobin to transport oxygen. Berg, et al.: pages 204 – 210 Garrett and Grisham: Chapter 15: Bottom of Page 491- 504 Assignment: Segel: Read pages 86-90 Page 93: Problems 53, 54, and 55.
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± Hemoglobin as a blood buffer HHgb + O 2 HHgbO 2 Breaking the salt linkage of His146 in the conversion of deoxyhemoglobin to oxyhemoglobin is accompanied by a change in pKa of that histidine residue since the carboxyl group becomes a much stronger acid when it is no longer bound in a salt linkage. pKa = 7.7 pKa = 6.2 Hgb HgbO 2 + H + + H + The oxygen binding and H + binding capacities of hemoglobin are not independent, but interrelated.
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If consider the deoxy form of hemoglobin: HHgb pKa = 7.7 Hgb + H + Ka = 2 x10 -8 The pH of blood is 7.4. Can calculate the ratio of the Bronsted base to Bronsted acid using the Henderson Hasselbalch equation. 7.4 = 7.7 + log [Hgb] [HHgb] [Hgb] [HHgb] = .5 Thus 1/3 of deoxyhemoglobin is Hgb 2/3 of deoxyhemoglobin is HHgb HHgbO 2 pKa = 6.2 HgbO 2 + H + Ka = 6.3 x10 -7 Can carry out same calculation for the oxy form of hemoglobin: Would get: [HgbO 2 ] = 94.1% [HHgbO 2 ] = 5.9%
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At any one time, hemoglobin is present in a mixture of oxygenated and deoxygenated forms. The proportion of each form depends on the concentration (partial pressure) of oxygen. Also, each of these forms will be a mixture of protonated and unprotonated forms,
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Lecture10 - /14/11 Background reading Assignment Segel Berg...

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