A novel nickel-containing superoxide dismutase from Streptomyces spp

Abstract

A novel type of superoxide dismutase (SOD) was purified to apparent homogeneity from the cytosolic fractions of Streptomyces sp. IMSNU-1 and Strep. coelicolor ATCC 10147 respectively. Both enzymes were composed of four identical subunits of 13.4 kDa, were stable at pH 4.0–8.0 and up to 70 °C, and were inhibited by cyanide and H₂O₂ but little inhibited by azide. The atomic absorption analyses revealed that both enzymes contain 0.74 g-atom of nickel per mol of subunit. Both enzymes were different from iron-containing SOD and manganese-containing SOD from Escherichia coli, and copper- and zinc-containing SODs from Saccharomyces cerevisiae and bovine erythrocytes, with respect to amino acid composition, N-terminal amino acid sequence and cross-reactivity against antibody. The absorption spectra of both enzymes were identical, exhibiting maxima at 276 and 378 nm, and a broad peak at 531 nm. The EPR spectra of both enzymes were almost identical with that of Ni^III in a tetragonal symmetry of Ni^III-oligopeptides especially containing histidine. The apoenzymes, lacking in nickel, had no ability to mediate the conversion of superoxide anion radical to hydrogen peroxide, strongly indicating that Ni^III plays a main role in these enzymes.