What is the Difference Between Hemocyanin and Hemoglobin?

Hemocyanin and hemoglobin are both respiratory pigments that facilitate gas exchange in the blood of various organisms. However, they have some key differences:

1. Structure and Composition: Hemocyanin is a copper-containing protein found in some marine invertebrates such as molluscs, squids, and arthropods like scorpions, spiders, and horseshoe crabs. Hemoglobin is an iron-containing protein found in the red blood cells of vertebrates.
2. Blood Cell Association: Hemocyanin is a free-floating protein in the hemolymph, while hemoglobin is bound to red blood cells.
3. Oxygen Binding Capacity: Hemocyanin is larger than hemoglobin and can bind 96 oxygen atoms, whereas hemoglobin can bind only four oxygen atoms.
4. Stability and Temperature: Hemocyanin is a more stable molecule that can function at temperatures up to 90°C and in cold climates, while hemoglobin is less efficient in such conditions.
5. Color: Hemocyanin gives the blood a blue color when oxygenated due to the presence of copper, while hemoglobin gives blood a red color when oxygenated due to the presence of iron.

Comparative Table: Hemocyanin vs Hemoglobin

Here is a table comparing the differences between hemocyanin and hemoglobin:

These differences highlight the unique properties of hemocyanin and hemoglobin, which facilitate gas exchange in invertebrates and vertebrates, respectively.