A novel type of superoxide dismutase (SOD) was purified to apparent ho
mogeneity 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 degrees 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 enzyme
s were different from iron-containing SOD and manganese-containing SOD
from Escherichia coli, and copper- and zinc-containing SODs from Sacc
haromyces cerevisiae and bovine erythrocytes, with respect to amino ac
id composition, N-terminal amino acid sequence and cross-reactivity ag
ainst 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 Nim in
a tetragonal symmetry of Ni-III-oligopeptides especially containing hi
stidine. The apoenzymes, lacking in nickel, had no ability to mediate
the conversion of superoxide anion radical to hydrogen peroxide, stron
gly indicating that Ni-III plays a main role in these enzymes.