As a highly reactive substance produced in biological systems by the one-electron reduction of oxygen, superoxide (O2-) seemed a likely candidate as a bactericidal agent in leukocytes. The reduction of cytochrome c, a process in which O2- may serve as an electron donor, was found to occur when the cytochrome was incubated with leukocytes. O2- was identified as the agent responsible for the leukocyte-mediated reduction of cytochrome c by the demonstration that the reaction was abolished by superoxide dismutase, an enzyme that destroys O2-, but not by boiled dismutase, albumin, or catalase.
Bernard M. Babior, Ruby S. Kipnes, John T. Curnutte