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 aligned amino acid sequences of iron-containing superoxide dimutases (Fe-SODs) and cambialistic SOD from Porphyromonas gingivalis, but is complementarily substituted with Gln-142 in manganese-containing SODs (Mn-SODs). In order to clarify the contribution of this exchange of Gin to the metal-specific activity of P. gingivalis SOD, we have prepared a mutant of the enzyme with conversions of Gln-70 to Gly and Ala-142 to Gin. The ratio of the specific activities 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 absorption 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 partially accounts for the metal-specific activity of the enzyme.