[Blue blood: structure and evolution of hemocyanin]

Hemocyanins are the oxygen-transporting proteins in arthropods and molluscs, the oxygen is bound by two copper atoms. Spectroscopic studies on the active site show similarities to the active site of a further group of copper-containing proteins, the tyrosinases. Arthropodan and molluscan hemocyanins form high-molecular aggregates which are markedly different in size and quaternary structure. There is only one tertiary structure of an arthropodan hemocyanin available, but from comparison of all amino acid sequences known so far from arthropodan hemocyanins, a common tertiary structure for all arthropodan hemocyanins can be deduced. Again, sequence comparison allows the construction of an evolutionary tree for some oxygen-binding copper proteins.