Monday, February 21, 2005

Why lobsters are blue

Well, I was enjoying myself at a party recently (attended by, among others, famed starlet of the web, Todd's Girl) when the question of lobsters came up.

I first took that as an opportunity to tell my hilarious story about the time I attached a lobster to my thumb in a Maine seafood restaurant (it's on Mile Road in Wells) and then jumped up screaming that I was being attacked. I thought better. It wasn't that funny at the time.

But people were wondering, why are lobsters blue when they're in the water. I didn't know, but I hate to admit such things. I did admit it, though, but I said that perhaps it had something to do with their blood. As most everyone knows, some people have a ruddy hue, and this comes from the presence of blood vessels close to the surface of their skin, combined with the relatively translucent nature of the dead skin of the epidermis. (It is interesting to note that there is a black nationalist group based in New York led by a man who denies the existence of white people. He once told a reporter interviewing him for the New York Press something along the lines of, "You're not white--look at yourself, man. You're red!)

In the case of humans and other vertebrates, the blood carries oxygen via hemoglobin, which is a protein that hosts four iron atoms, and they appear red when the iron is oxidized, for the same reason that rust and Mars are red. In the case of some invertebrates, including the arthropods, which includes lobsters, oxygen is carred around by a protein called hemocyanin, which moves around the animals in a fluid called hemolymph, rather than blood. Hemocyanin is colorless when not binding oxygen, and blue when it is. So, I said at the party, perhaps lobsters are blue because their "blood" is blue when oxygenated.

I thought that was a good effort--as every politican knows, when asked a question he either can't answer or doesn't want to answer, he ought to answer a different question, one that he can answer and wants to.

But I, unlike a politican in most ways, would like to be able to give an answer. And, what did I find when I got to work last Monday morning, but an article about a paper that answered the very question posed two nights previously.

I was pretty far off the mark. It turns out that lobsters are blue or black because of pigment in their exoskeletons called astaxanthin. It also turns out that the fact was already well known. When lobsters are cooked, the structure of the pigment, which is made of two astaxanthin molecules crossed as an X, changes, as do the interactions between the two crossed molecules. This changes the way the molecules absorb light, and thus the color of a lobster, turning it red.


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