Wednesday, May 6, 2009

Horseshoe Crab Blood, Hemocyanin and Blood Clots

Horseshoe crabs are primitive animals, and I found out yesterday that they have blue blood. That was going to be my post. Look at the cool blue color:

As you can see -- milky blue. The blue color is caused by the hemocyanin in their blood, rather than hemoglobin. Hemocyanin is based on copper rather than iron. It is not uncommon undersea non-vertebrates, being in mollusks and octopus too. There is lots of detail on Wikipedia.

However, it is even more interesting that horseshoe crab blood has an unusual anti-bacterial property. 

Horseshoe crab blood, as discovered by Fred Band in 1956, contains Limulus Amebocyte Lysate  a which causes clots in response to lipopolysacchrides of the kind found in bacteria. The clotting occurs quickly and isolates the bacteria from the rest of the crab. It is useful pharmaceutically to detect bacterial contamination. This can detect roughly 10E6 organisms/ml, depending on the organism and many other factors. Actually this does not sound that sensitive to me, but it seems that other methods are worse.

Recently, this has created a market in wild horseshoe crab blood. The crabs are milked and then released. It seems that it is difficult to culture the cells that produce limulus amebocyte lysate in the lab, and that the wild-caught production will continue for a while.