The bicarbonate/carbon dioxide pair increases hydrogen peroxide-mediated hyperoxidation of human peroxiredoxin 1.

2-Cys peroxiredoxins (Prxs) rapidly reduce HO, thereby acting as antioxidants and also as sensors and transmitters of HO signals in cells. Interestingly, eukaryotic 2-Cys Prxs lose their peroxidase activity at high HO levels. Under these conditions, HO oxidizes the sulfenic acid derivative of the Prx peroxidatic Cys (CSOH) to the sulfinate (CSO) and sulfonated (CSO) forms, redirecting the CSOH intermediate from the catalytic cycle to the hyperoxidation/inactivation pathway. The susceptibility of 2-Cys Prxs to hyperoxidation varies greatly and depends on structural features that affect the lifetime of the CSOH intermediate. Among the human Prxs, Prx1 has an intermediate susceptibility to HO and was selected here to investigate the effect of a physiological concentration of HCO/CO (25 mm) on its hyperoxidation. Immunoblotting and kinetic and MS/MS experiments revealed that HCO/CO increases Prx1 hyperoxidation and inactivation both in the presence of excess HO and during enzymatic (NADPH/thioredoxin reductase/thioredoxin) and chemical (DTT) turnover. We hypothesized that the stimulating effect of HCO/CO was due to HCO, a peroxide present in equilibrated solutions of HO and HCO/CO Indeed, additional experiments and calculations uncovered that HCO oxidizes CSOH to CSO with a second-order rate constant 2 orders of magnitude higher than that of HO ((1.5 ± 0.1) × 10 and (2.9 ± 0.2) × 10 m·s, respectively) and that HCO is 250 times more efficient than HO at inactivating 1% Prx1 per turnover. The fact that the biologically ubiquitous HCO/CO pair stimulates Prx1 hyperoxidation and inactivation bears relevance to Prx1 functions beyond its antioxidant activity.