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

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.