Some blood runs blue
Octopuses, horseshoe crabs, and many other animals carry oxygen with copper-based hemocyanin. Oxygenated, it is blue.
Established2 min read
Hemocyanin floats free in the hemolymph rather than sitting in cells. Deoxygenated it is colourless; bound to oxygen it is blue. Horseshoe crabs, spiders, scorpions, cephalopods, and many crustaceans use it. The pigment is ancient and was worked out in the nineteenth century.
The same blue blood saves human lives for a mundane reason. Horseshoe-crab amebocytes clot in the presence of bacterial endotoxin. The limulus amebocyte lysate test screens vaccines and intravenous drugs. A 450-million-year body plan became a sterility assay.
Caveats
- Not every ‘blue’ animal is using hemocyanin. Some colours are structural.
- The pharmaceutical bleed is regulated and increasingly replaced by a synthetic factor. The biochemistry is unchanged.
Sources
- 1Bang F. B.. A Bacterial Disease of Limulus polyphemus. Bulletin of the Johns Hopkins Hospital 98, 1956.