Built-in co-operativity of oxygen binding by arthropod hemocyanins

Oxygen binding by arthropod hemocyanin from the scorpion Leirus quinquestriatus and the crabs Telphusa fluviatilis and Ocypoda cursor was studied in Ca²⁺, Mg²⁺-free solutions. The binding was found to be co-operative in all three cases. Our results and a re-examination of the literature lead us to conclude that co-operative oxygen binding is a built-in feature common to arthropod hemocyanins, distinguishing them from mollusc hemocyanins where co-operativity is conditional upon the presence of Ca²⁺ or Mg²⁺.