Bicarbonate increases peroxiredoxin 1 susceptibility to hyperoxidation

Peroxiredoxins (Prx) are abundant thiol peroxidases that react rapidly with H 2 O 2, constituting an important antioxidant defense and acting as sensors and transmitters of H 2 O 2 signals in cells. Certain Prxs are readily inactivated by H 2 O 2 at submillimolar concentrations, whereas others are less sensitive. This oxidative inactivation, or hyperoxidation, occurs when H 2 O 2 further reacts with the Cp-SOH producing Cp-SO 2 - and/or Cp-SO 3 - . Since HCO 3 - accelerates several of the reactions of H 2 O 2 with biothiols, we examined whether HCO 3 - could increase recombinant human peroxiredoxin 1 (Prx1) hyperoxidation by H 2 O 2 . Kinetic studies of NADPH consumption by Prx1 in presence of yeast Trx, yeast Trr and various H2O2 concentrations in the absence and presence of HCO 3 - (25 mM) provided values of Chyper1% of 335 µM and 110 µM, respectively. Western blot (with an antiPrx-SO 3 - /SO 2 - antibody) analyses and Nano-ESI-Q-TOF MS/MS analyses of incubations of Prx1 (2.5 µM) and H 2 O 2 (25 µM) showed higher levels of hyperoxidized Prx1 in the presence of HCO 3 - (25 mM) than in its absence. Taken together, the results indicate that bicarbonate increases Prx1 susceptibility to hyperoxidation by H 2 O 2. We discuss the possible mechanism of the process and its biological implications. (FAPESP13/07937-8)