Hemerythrins

Hemerythrins are oxygen-binding proteins found in certain invertebrates, such as marine polychaete worms and priapulid worms. They are distinct from the more commonly known oxygen-binding proteins, hemoglobin and hemocyanin, in terms of their structure and the metal ions they utilize. Hemerythrins contain non-heme iron atoms, specifically two iron ions per protein subunit, which are responsible for their oxygen-binding capability.

The structure of hemerythrins is typically octahedral, with the iron ions coordinated by amino acid residues from the protein. In their oxygenated form, the iron ions are in the +2 and +3 oxidation states, forming a μ-oxo bridge. This unique structure allows hemerythrins to bind and release oxygen efficiently, facilitating respiratory functions in the organisms that possess them.

Hemerythrins are often found in specialized cells called hemerythrocytes, which are analogous to the red blood cells in vertebrates that contain hemoglobin. These cells transport oxygen from respiratory surfaces, such as gills, to various tissues throughout the body. The oxygen-binding properties of hemerythrins can be influenced by factors such as pH and the presence of other molecules, allowing for fine-tuned regulation of oxygen delivery.

The study of hemerythrins provides valuable insights into the diversity of respiratory proteins and the evolutionary adaptations of invertebrates to their environments. Understanding the structure and function of hemerythrins contributes to broader knowledge in the fields of biochemistry, molecular biology, and comparative physiology.