hemerythrocytes

Hemerythrocytes are non-iron containing, non-heme iron proteins found in the blood of certain marine invertebrates, such as brachiopods and annelids. Their primary function is oxygen transport, similar to hemoglobin in vertebrates. Unlike hemoglobin, which contains iron in a heme group, hemerythrocytes bind oxygen directly to the iron atoms within the protein structure itself. This results in a pale violet color when oxygenated, contrasting with the red color of oxygenated hemoglobin. The iron atoms are typically present in a di-iron center. The oxygen binding capacity of hemerythrocytes is generally lower than that of hemoglobin. The structure of hemerythrocytes is also distinct from hemoglobin, often existing as multi-subunit proteins. The presence of hemerythrocytes is an adaptation to low-oxygen environments, providing an efficient means of oxygen delivery to tissues in these organisms.