Superoxide dismutase and NADH diaphorase in haemerythrocytes of sipunculans

Abstract

1. 1. Two enzymes, superoxide dismutase (EC 1.15.1.1) and NADH diaphorase (EC 1.6.99.3) known, respectively, for inhibiting autoxidation of haemoglobin to methaemoglobin and for reducing methaemoglobin back to functional haemoglobin in mammalian erythrocytes, are also present in purified haemerythrocytes of five species of sipunculans. 2. 2. There are two distinct superoxide dismutases in sipunculans, and also two distinct NADH diaphorases. Variation of superoxide dismutases resembles patterns of genetic polymorphism found in these enzymes in mammals, and the major superoxide dismutase and NADH diaphorase of sipunculans each bave patterns of polymorphism compatible with the suggestion that the molecules are dimers with identical subunits. 3. 3. Although there is absolute tissue specificity of haemerythrin in that distinct haemerythrins occur in muscle (myohaemerythrin, coelomic haemerythrocytes and vascular haemerythrocytes, there are no corresponding absolute differences among either NADH diaphorases or superoxide dismutases. 4. 4. Sipunculan superoxide dismutase I has a molecular weight near 40,000, whereas sipunculan superoxide dismutase II has a molecular weight of 180,000. The molecular weight of NADH diaphorase II from Phascolosoma arcuatum is 72,000. 5. 5. It is suggested that haemerythrin and superoxide dismutase have certain similarities in chemical structure and physiological function, and there is evidence in the literature on primary structure suggestive of distant homology between sipunculan haemerythrins, on one hand, and Fe- and Mn-superoxide dismutases, on the other.