Hemeryhmien

Hemeryhmien, known in English as hemerythrins, are a family of non-heme iron-containing oxygen-carrying proteins found in a variety of invertebrates. Unlike vertebrate hemoglobins, hemerythrins do not contain heme groups. Instead, oxygen binding occurs at a di-iron center coordinated by histidine and carboxylate ligands from the protein. The surrounding protein environment supports reversible binding of O2.

Biological role and distribution: In species that express hemerythrins, these proteins are typically soluble in the circulatory fluid (hemolymph) and can function as oxygen transporters or storage molecules. They are especially associated with organisms living in low-oxygen environments or during life stages requiring rapid oxygen delivery. Hemerythrins have been found in several invertebrate groups, including brachiopods, some annelids, sipunculans, and certain arthropods.

Structure and chemistry: The hallmark feature of hemerythrins is the di-iron active site, which is essential for oxygen binding. Many hemerythrin molecules can form multimeric assemblies, and the protein’s redox-active center contributes to the distinctive spectroscopic properties of the oxygenated and deoxygenated forms. Oxygenation often produces a noticeable color change, which historically aided detection and study.

Evolution and significance: Hemerythrins represent an independent solution to oxygen transport in invertebrates, separate from the heme-based systems of hemoglobins and hemocyanins. Their distribution and function illustrate the diversity of biological strategies for managing oxygen in varying ecological niches. See also: hemoglobin, hemocyanin, myoglobin, oxygen transport proteins.