1. In class, we discussed how the molecule 2,3-bisphosphoglycerate (BPG) is an allosteric regulator of hemoglobin (Hb). Answer the following questions about BPG and its regulation of oxygen binding: a) Would BPG have any effect on myoglobin's ability to bind or release oxygen? If so, describe how BPG would affect myoglobin. If not, explain why. b) The image below depicts BPG bound to Hb. The ? subunits are depicted in dark gray, and the ? subunits in light gray. Use the MWC model of concerted allostery to explain how BPG binding influences the conformation of Hb. c) Based on the observation that BPG binds preferentially to partially deoxygenated Hb, briefly explain (1-2 sentences) where BPG is most likely to be most effective on Hb function within the body. How does BPG binding to Hb alter the equilibrium of oxygen binding?
Added by Lorena D.
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Step 1: BPG does not affect myoglobin's ability to bind or release oxygen because myoglobin does not show any efficient role in oxygen transfer. Show more…
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Biphosphoglycerate (BPG) binds to hemoglobin (Hb), answer the following question: 1. Which part of the hemoglobin structure BPG binds to (10%)? 2. Which state of Hb does BPG has higher affinity (10%)? 3. Using the oxygen binding curve of Hb, explain why increased BPG concentration from 4 mM to 8 mM in erythrocyte is a fast-adaptive approach the body uses to cope with high-altitude. Provided that the arterial pO2 at sea level is 100 torr, and 55 torr at 4500 m altitude, whereas the venous pO2 remains at 28 torr (65%). 4. What are the three forms CO2 is transported in body (15%)?
Madhur L.
Sometimes confusion arises over the mechanism of BPG action. Since it influences oxygen binding, folks want to put it where the O2 is. In looking at the 3D model on the thinkbio website (BPG: molecular modifier), BPG is shown in the middle. Oxygen is bound by the iron in the heme, which is the structure in light gray (small balls) at lower left and upper right. There's no way BPG could directly interfere with oxygen's ability to bind to heme. Note also that BPG is bound between hemoglobin subunits, whereas heme binds to each subunit. One cause of the misconception is that oxygen, being a very electronegative atom, often has a partial negative charge in molecules. In oxygen gas (O2) the electrons would, of course, be shared equally.
Suman K.
Hemoglobin (Hb) is a blood protein that is responsible for transporting oxygen. It can exist in the protonated form as $\mathrm{HbH}^{+}$. The binding of oxygen can be represented by the simplified equation $$\mathrm{HbH}^{+}+\mathrm{O}_{2} \rightleftharpoons \mathrm{HbO}_{2}+\mathrm{H}^{+}$$ (a) What form of hemoglobin is favored in the lungs where oxygen concentration is highest? (b) In body tissues, where the cells release carbon dioxide produced by metabolism, the blood is more acidic due to the formation of carbonic acid. What form of hemoglobin is favored under this condition? (c) When a person hyperventilates, the concentration of $\mathrm{CO}_{2}$ in his or her blood decreases. How does this action affect the above equilibrium? Frequently a person who is hyperventilating is advised to breathe into a paper bag. Why does this action help the individual?
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