Pulse radiolysis studies on superoxide reductase from Treponema pallidum

Superoxide reductases (SORs) are small metalloenzymes, which catalyze reduc tion of O-2(.-) to H2O2. The reaction of the enzyme from Treponema pallidum with superoxide was studied by pulse radiolysis methods. The first step is an extremely fast hi-molecular reaction of tile ferrous center with O-2(.- ), with a rate constant of 6 x 10(8) M-1 s(-1). A first intermediate is for med which is converted to a second one with a slower rate constant of 4800 s(-1), This latter value is 10 times higher than the corresponding one prev iously reported in the case of SOR from Desulfoarculus baursii. The reconst ituted spectra for the two intermediates are consistent with formation of t ransient iron-peroxide species. (C) 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.