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Why are iron-containing proteins important for oxygen transport and electron-transfer reactions?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — transition metal Modern version of the periodic table of the elements (printable).

Iron is the most widespread transition metal in biological systems, and its ability to exist in multiple oxidation states makes it uniquely suited for critical physiological processes.12

Oxygen Transport

In proteins like hemoglobin, iron atoms are housed within heme groups. The iron atom acts as a binding site that forms an unstable, reversible bond with oxygen molecules as blood circulates between the lungs and body tissues. This reversible nature is essential for the effective uptake and release of oxygen throughout the organism.3

Electron-Transfer Reactions

Iron-containing proteins, such as cytochromes and ferredoxin, are vital for electron transfer (oxidation-reduction) reactions. During these processes, an iron atom within the protein accepts an electron—becoming reduced—and subsequently transfers that electron to another carrier, thereby oxidizing itself. This ability to shuttle electrons is fundamental to energy metabolism and processes like photosynthesis, where iron-containing cofactors facilitate the movement of electrons between molecules.14