  Superoxide reductases (SORs) are small metalloenzymes, which catalyze
reduction of O2*- 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 bi-molecular reaction of the ferrous center with O2, with a rate
constant of 6 x 10 (8) M(-1) s(-1). A first intermediate is formed 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 previously reported
in the case of SOR from Desulfoarculus baarsii. The reconstituted spectra for
the two intermediates are consistent with formation of transient iron-peroxide
species.
