Pulse radiolysis studies on superoxide reductase from Treponema pallidum

TL;DR

This study uses pulse radiolysis to investigate the rapid reaction mechanisms of superoxide reductase from Treponema pallidum, revealing fast reaction rates and transient iron-peroxide intermediates.

Contribution

It provides the first detailed kinetic and spectroscopic analysis of T. pallidum SOR, highlighting differences from other species and elucidating reaction intermediates.

Findings

Fast bi-molecular reaction rate of 6 x 10^8 M^-1 s^-1

Identification of two transient intermediates with specific spectra

Reaction rate of the second intermediate is ten times higher than in D. baarsii

Abstract

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.