Hemocyanin from Dolabella auricularia

Binding of Ca2+ ion by calcium-depleted Dolabella hemocyanin was studied by means of equilibrium dialysis and H+ ion titration. It was inferred from the analysis of the data that H+ ion competes with Ca2+ ion for the binding sites. The mole of the Ca2+ ion binding sites in hemocyanin was 1.7 per minimum molecular unit (27,900 g protein containing one g-atom copper). The dissociation constants for Ca2+ and H+ ions were 2.5×10−4 and 5.6×10−7M, respectively. The refractivity index for a solution of EDTA-treated hemocyanin was decreased by addition of Ca2+ ion, and the volume change was calculated from the decrement in refractivity to be +110 ml per 27,900 g protein, according to Ikegami's equation (l).