Porphyromonas gingivalis contains a single constitutive superoxide dismutase (SOD) that is active with either iron or manganese at the active site. The aim of this work was to evaluate the effect of the Leu ₇2 to Trp mutation on the structure of P. gingivalis SOD (Pg SOD) using lectrophoretic characterization. Leu ₇2, which is located near the active site metal, is substituted with Trp in aligned amino acid sequences of iron–containing SOD. The results of electrophoretic characterization and the expressed activity of mutant SOD suggest that mutant SOD have the same gross structure as wild–type SOD. We herein conclude that the integrity of Leu ₇2 is a necessary requisite for the metal–tolerant activity of Pg SOD