Spider hemocyanin binds ecdysone and 20-OH-ecdysone

Fluorescence quenching studies and binding experiments with [H-3]ecdysone r eveal that the respiratory protein, hemocyanin, of the tarantula Eurypelma californicum binds ecdysone, The binding constant for ecdysone ranges betwe en 0.5 and 5 mM, indicating a low affinity binding. However, it is comparab le with those found for the ecdysone binding to hexamerins from insects. Ba sed on a comparison of sequences and x-ray structures of arthropodan hemocy anins, we propose an evolutionary conserved hydrophobic pocket in domain 1 of the hemocyanin subunit that may bind ecdysone.