Kinetic study of the reaction of glutathione peroxidase with peroxynitrite

Glutathione peroxidases and their mimics, e.g., ebselen or dialyl tellurides, efficiently reduce peroxynitrite/peroxynitrous acid (ONOO-/ONOOH) to nitrite and protect against oxidation and nitration reactions. Here, we report the second-order rate constant for the reaction of the reduced form of glutathione peroxidase (GPx) with peroxynitrite as (8.0 +/- 0.8) x 10(6) M-1 s(-1) (per GPx tetramer) at pH 7.4 and 25 degrees C. The rate constant for oxidized GPx is about 10 times lower, (0.7 +/- 0.2) x 10(6) M-1 s(-1), On a selenium basis, the rate constant for reduced GPx iu similar to that obtained previously fur ebselen. The data support the conclusion that GPx can exhibit a biological function bg acting as a peroxynitrite reductase.