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Chapter 23: Problem 58

The \(\mathrm{Co}^{2+}\) -porphyrin complex is more stable than the \(\mathrm{Fe}^{2+}\) -porphyrin complex. Why, then, is iron the metal ion in hemoglobin (and other heme-containing proteins)?

Short Answer

Expert verified
Despite the fact that \(\mathrm{Co}^{2+}\)-porphyrin complex is more stable, iron is the metal ion in hemoglobin because of its ability to switch between the +2 and +3 oxidation states, which enables it to bind and release oxygen. Cobalt cannot interact with oxygen in the same way, and the human body has not evolved to metabolize and regulate cobalt as it does with iron.

Step by step solution

01

Understanding the Role of Iron

Iron, specifically in the form of \(\mathrm{Fe}^{2+}\), is used in heme proteins such as hemoglobin because of its unique ability to interact with oxygen and to switch between its +2 and +3 oxidation states. This lets it bind to oxygen in the lungs and then release it where it's needed in the body.
02

Implications of Replacement

Cobalt, while forming a more stable complex with porphyrin, does not have the same properties as iron. The \(\mathrm{Co}^{2+}\) is not capable of interacting with oxygen in the same way as \(\mathrm{Fe}^{2+}\). Thus, if cobalt were to replace iron, it could disrupt the oxygen transport function of hemoglobin and other heme proteins.
03

Detailing the Biological Context

Furthermore, the human body has evolved to metabolize and regulate the concentrations of iron, but not cobalt. Including cobalt instead of iron would require a different biochemical pathway. So even though the \(\mathrm{Co}^{2+}\) -porphyrin complex is more stable, iron is more suitable for the role in heme proteins.

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