A comparative study on the binding characteristics of the tight serum biliverdin-protein complexes in two fishes: Anguilla japonica and Clinocottus analis.

The binding characteristics of biliverdin to its carrier protein in the blue-green blood of Clinocottus analis (woolly sculpin) and Anguilla japonica (freshwater eel) were operationally defined by various chemical probing methods and spectra analysis. The biliverdin in C. analis is a rotatable coiled molecule enveloped in a hydrophobic pocket of its carrier protein. The biliverdin in A. japonica is an open form molecule with external hydrogen bond or weak ester bond interacting with the carrier protein. This, for the first time, shows that the novel firm binding biliprotein complexes in the blood of different species are biochemically different. Their comparative and evolutionary significance is discussed.