Properties of hemocyanins—I. The effect of calcium ions on the oxygen equilibrium of crayfish hemocyanin

Abstract

1. 1. The oxygen affinity of hemocyanin from the crayfish, Procambarus simulans, is greatly decreased by dialysis between pH 6·5 and 8·0. This effect is largely reversed by 10 mM calcium or by 60 mM magnesium. 2. 2. The data do not conform to Hill's equation, since the value of n increases with degree of oxygenation and is a function both of the calcium concentration and of pH. At low degrees of oxygenation n≅1·5 and is independent of pH or calcium, while at high oxygenation levels n increases with either pH or calcium. 3. 3. The importance of calcium in controlling the degree of dissociation of hemocyanin into subunits is known. Since the calcium concentration in crayfish blood changes during the molting cycle, it seems possible that calcium may play a role in modifying the oxygen transport function of hemocyanin by changing the degree of aggregation.