In: Chemistry
1. Carbon monoxide (CO) normally binds tightly to heme (aq). How is this decreased in Mb? What are the relative CO vs. O2 binding strengths in each case?
2. Explain the role of BPG in Hb function. How is BPG involved with adaptation to high altitude? Draw and label a graph that illustrates Hb at low and high altitude.
Answer 1: Hemoglobin (Hb) is a tetramer of two αand two β subunits held together by inter molecular force and 4 bound hemes, each of which can bind a dioxygen (O2). Myoglobin (Mb) is a single polypeptide chains which has higher affinity for dioxygen than Hb. Myoglobin contains a porphyrin ring with an iron at its center. A proximal histidine group is attached directly to iron, and a distal histidine is in the opposite face. The distal imidazole is not bonded to the iron but is available to interact with the substrate O2. This interaction encourages the binding of O2, but not carbon monoxide (CO). Dissolved oxygen in the blood binds to the hemoglobin (Hb) in red blood cells according to the following reversible reaction.
Hb(aq)+4O2(aq) ⇌ Hb(O2)4(aq)
The bonds between hemoglobin and carbon monoxide are about 300 times as strong as those with oxygen. Carbon monoxide binds to hemoglobin even more tightly than oxygen. The following occurs:
Hb(aq) + 4CO(aq) ⇌ Hb(CO)4(aq)