The existence of unpaired electrons in ground state O2 and the need for spin conservation favor the univalent re duction pathway. The intermediates encountered on this pathway, O2-, H2O2 and HO· threaten the genetic and structural integrity of aerobic cells; thus defenses are needed. The best defense is avoidance and that is provided by the cupro-hemo enzyme cytochrome c oxidase, which manages the tetravalent reduction of O2 to 2 H20 without releasing intermediates. Were all biological oxygen reduction due to cytochrome c oxidase, there would be no problem. There are both enzymic and spontaneous reduction of O 2, which do proceed by the univa lent pathway; thus other defenses are essential. These are provided by superoxide dismutases, which convert O2- into O 2 and H2O 2, and by catalases and peroxidases which deal with the H2O 2: the catalases by dismuting it to H2O + O 2 and the peroxidases by catalyzing its reduction to H2O. The physico-chemical character of these enzymes, as well as their mechanisms of action, will be discussed, as will pathologies in which oxygen radicals appear to play a major role.
Professor Fridovich received his B.S. degree from the City College of New York in 1951 and his Ph.D. in Biochemistry in 1955. He has been associated with Duke University since 1956 and has been the James B. Duke Professor of Biochemistry since 1976. He has served on several editorial boards (Advances in Free Radicals in Biology and Medicine, Biochimica Biophysica Acta) and is a member of the New York Academy of Sciences. He was named the Senior Passano Foundation Laureate in 1987. His professional memberships include Phi Beta Kappa, The American Society of Biological Chemists and the American Academy of Arts and Sciences.