Positive cooperativity in binding carbon monoxide to hemocyanin

The binding of carbon monoxide to hemocyanin from the crab Scylla serrata has been studied by thin layer optical absorption and front face fluorescence techniques. The binding to the monomeric form is completely noncooperative whereas the binding to the native oligomeric form is found to be weakly but definitely cooperative. An analysis based on the MWC model of the oxygen and carbon monoxide binding curves indicates that the allosteric constant, L, describing the equilibrium between the 2 unligated forms is different for each ligand. This implies that at least 3 allosteric forms are needed to characterize the binding of oxygen and carbon monoxide to this hemocyanin.