The Kinetics of the Reaction of Thiocyanate and Nitrite Ions with Orconectes limosus Oxyhemocyanin

Abstract

Abstract The time course of the reaction of oxyhemocyanin from the arthropod Orconectes limosus with SCN− and NO2− was investigated. After addition of one of these anions to oxyhemocyanin solu­tion an exponential decay of A340 was found, indicating a removal of oxygen from the active site. The order of reaction with respect to ligand was about 3 for thiocyanate and about 1 for nitrite. On this basis, a possible arrangement of ligands in the active site has been proposed. The final product of reaction with SCN− yielded a mononuclear copper EPR spectrum while the reaction product with NO2− gave a characteristic spectrum of two coupled Cu2+ ions. It was possible to remove the ligands from the active site by dialysis. The reaction patterns showed distinct changes in a narrow pH range, 5.3-6.5. A possible effect of structural alterations of the protein moiety on the course of the reaction of oxyhemocyanin with ligands is suggested.