The decomposition of hydrogen peroxide by hemocyanin and by its dissociation products

Abstract

The experiments reported in this paper give evidence for the ability of hemocyanin to decompose hydrogen peroxide catalytically. This property was common to all the hemocyanins studied (Molluscan and Crustacean hemocyanins). Any possibility that this catalytic property could be due to a catalase incidentally present in the blood or linked to the hemocyanin molecule must be excluded. Not only was iron never found in the protein preparations, but the study of the activity showed several striking differences from that of catalase, among them the pH-activity curve and the action of substrate concentration. Whereas a high concentration of H 2O 2 inhibits Fe porphyrin catalase activity, it had no effect at all on the catalase activity of hemocyanin. The decomposition of hydrogen peroxide catalyzed by hemocyanin is due to the presence of copper. Removal of the metal from the protein brings loss of activity. The activity is restored to the same level when hemocyanin is reconstituted. Hemocyanin from different sources does not have the same activity as calculated per unit of copper. Hemocyanin from Helix, e.g., with a molecular weight of 8,000,000 and a copper content of 0.25%, had activity toward H 2O 2 2.5 times less than that of Octopus hemocyanin which has a molecular weight of 2,800,000 and the same copper content. Moreover, equivalent amounts of inorganic copper had no effect upon H 2O 2 as demonstrated manometrically.