ALLOSTERIC PROPERTIES AND THE ASSOCIATION EQUILIBRIA OF HEMOCYANIN FROM CALLIANASSA-CALIFORNIENSIS

The influence of magnesium ions, hydrogen ions, and oxygen on the monomer (17 S)-tetramer (39 S) equilibrium of the hemocyanin from Callianassa californiensis has been investigated. Data have been interpreted in terms of a theory integrating the allosteric equilibria and association equilibrium. Binding of oxygen and divalent cations by the hemocyanin has also been studied in terms of the theory, and the parameters in the model have been determined. The 17 S monomer, which contains six polypeptide chains, is found to be the allosteric unit which behaves as a self-contained co-operative system with allosteric properties. Both magnesium and hydrogen ions are shown to affect the association directly, whereas the effect of oxygen binding can be explained in terms of a difference in the allosteric equilibrium constant L′ in the different associated states of the protein. It is shown that whereas the effect of oxygen on the monomer-tetramer equilibrium is easily observable, the converse effect of the association equilibrium on the oxygen binding curve is at the limit of detectability. © 1979.