Hemerythrin vs. Hemocyanin

Attribute	Hemerythrin	Hemocyanin
Metal ion	Iron	Copper
Color	Red	Blue
Function	Oxygen transport and storage	Oxygen transport
Structure	Tetrameric	Hexameric

Structure

Hemerythrin and hemocyanin are two types of respiratory proteins found in certain invertebrates. Hemerythrin is a non-heme iron protein, while hemocyanin is a copper-containing protein. Hemerythrin contains two iron atoms per subunit, while hemocyanin has two copper atoms per subunit. The structure of hemerythrin consists of four subunits, each containing a single iron-binding site. In contrast, hemocyanin typically consists of multiple subunits arranged in a quaternary structure.

Oxygen Binding

One of the key differences between hemerythrin and hemocyanin is how they bind oxygen. Hemerythrin binds oxygen directly to the iron atoms in its structure. When oxygen binds to hemerythrin, the iron atoms undergo a change in oxidation state. In contrast, hemocyanin uses copper atoms to bind oxygen. The copper atoms in hemocyanin are in the cuprous state when oxygen is not bound, and they switch to the cupric state when oxygen binds.

Color

Another noticeable difference between hemerythrin and hemocyanin is their color. Hemerythrin is typically colorless when oxygen is not bound to it. However, when oxygen binds to hemerythrin, it turns a pink or red color. This color change is due to the oxidation of the iron atoms in hemerythrin. On the other hand, hemocyanin is blue in color when oxygen is bound to it. The blue color of hemocyanin is a result of the copper atoms binding to oxygen.

Function

Both hemerythrin and hemocyanin play crucial roles in oxygen transport in the organisms that possess them. Hemerythrin is found in certain marine invertebrates, such as sipunculids and brachiopods. It functions to transport oxygen from the environment to the tissues of these organisms. Hemocyanin, on the other hand, is found in arthropods and mollusks. It serves a similar function to hemerythrin, transporting oxygen through the hemolymph of these organisms.

Evolutionary History

The evolutionary history of hemerythrin and hemocyanin is also quite different. Hemerythrin is believed to be an ancient protein that predates the evolution of hemocyanin. It is thought to have originated in early marine organisms and has been conserved in certain lineages throughout evolution. Hemocyanin, on the other hand, is believed to have evolved later in the evolutionary history of invertebrates, likely as an adaptation to different environmental conditions.

Environmental Adaptations

One of the reasons for the different evolutionary histories of hemerythrin and hemocyanin may be their adaptations to different environmental conditions. Hemerythrin is more efficient at binding oxygen at low oxygen concentrations, making it well-suited for organisms living in oxygen-poor environments. In contrast, hemocyanin is better at binding oxygen at high oxygen concentrations, which may be advantageous for organisms living in well-oxygenated environments.

Conclusion

In conclusion, hemerythrin and hemocyanin are two distinct respiratory proteins found in invertebrates. While both proteins play a crucial role in oxygen transport, they differ in their structure, oxygen-binding mechanisms, color, evolutionary history, and environmental adaptations. Hemerythrin utilizes iron atoms to bind oxygen and is typically colorless until oxygen binds, turning it pink or red. Hemocyanin, on the other hand, uses copper atoms to bind oxygen and is blue in color when oxygen is bound. These differences highlight the diverse strategies that organisms have evolved to meet their oxygen transport needs.