Binding of oxygen and carbon monoxide to the hemocyanin from the spiny lobster

A high precision, two-dimensional study of oxygen and carbon monoxide binding to Panulirus interruptus hemocyanin has been carried out. Global data analysis of three types of experiments, probing the molecule in its various states of CO and O2 ligation, revealed the entire hexamer to be the basic allosteric unit involved in a two-state mechanism. The co-operativity and linkage of the two ligands are presented in terms of derivative Hill plot surfaces extended along co-ordinates of CO and O2 activities giving a detailed and comprehensive view of the binding behavior. Among the findings is an apparent high co-operativity of carbon monoxide binding at high oxygen activity. The results are discussed in view of a general mechanism for co-operative behavior found in larger hemocyanin aggregates concerning "nested" allosteric interactions.