A change of the metal-specific activity of a cambialistic superoxide dismutase from Porphyromonas gingivalis by a double mutation of Gln-70 to Gly and Ala-142 to Gln
By. Hiraoka et al., A change of the metal-specific activity of a cambialistic superoxide dismutase from Porphyromonas gingivalis by a double mutation of Gln-70 to Gly and Ala-142 to Gln, BIOCHEM J, 345, 2000, pp. 345-350
Gln-70, which is located near the active-site metal, is conserved in aligne
d amino acid sequences of iron-containing superoxide dimutases (Fe-SODs) an
d cambialistic SOD from Porphyromonas gingivalis, but is complementarily su
bstituted with Gln-142 in manganese-containing SODs (Mn-SODs). In order to
clarify the contribution of this exchange of Gin to the metal-specific acti
vity of P. gingivalis SOD, we have prepared a mutant of the enzyme with con
versions of Gln-70 to Gly and Ala-142 to Gin. The ratio of the specific act
ivities of Mn- to Fe reconstituted P. gingivalis SOD increased from 1.4 in
the wild-type to 3.5 in the mutant SODs. Furthermore, the visible absorptio
n spectra of the Mn-and Fe-reconstituted mutant SODs more closely resembled
that of Mn-specific SOD than that of the wild-type SOD. We conclude that a
difference in cofiguration of the Gin residues of P. gingivalis SOD partia
lly accounts for the metal-specific activity of the enzyme.