Haematoporphyrin enhances the peroxidase activity of haemoglobin

Abstract

The effect of haematoporphyrin, a component of some of the widely used anticancer drugs, on the peroxidase activity of haemoglobin has been studied. Haematoporphyrin increases the haemoglobin-catalysed hydrogen peroxide-mediated oxidation of o-dianisidine or NADH. Spectrophotometric study reveals that an interaction occurs between haemoglobin and haematoporphyrin which leads to a conformational change of the protein. The extent of enhanced peroxidase activity as well as conformational change of the protein vary in a positive manner with the stoichiometric ratio of haematoporphyrin/haemoglobin. An increase in the peroxidase activity of haemoglobin was also observed in the presence of superoxide dismutase, which catalysed the removal of superoxide anion generated during autoxidation of haemoglobin. Possible mechanisms underlying the relation between the conformational change of haemoglobin due to its interaction with haematoporphyrin and the enhanced peroxidase activity are discussed.