Hemocyanins in spiders, XVII. A presumptive active-site sequence of arthropod hemocyanins

Peptides containing the sequence -His-His-Trp-His-Trp-His- have been isolated from the subunits e and a of tarantula (Eurypelma californicum) hemocyanin and III B of Limulus polyphemus hemocyanin. In view of the published spectroscopic and titration data on the copper-polypeptide complex and the strong quenching effect of oxygenation on hemocyanin fluorescence, it is concluded that this sequence represents the major part of the active site of Eurypelma, Limulus, and possibly other arthropod hemocyanins.