[Properties of the catalytic center of a secretory 28kDa protein (1-cys peroxiredoxin) from rat olfactory epithelium].

The secretory 28 kD protein, an abundant water-soluble protein from rat olfactory epithelium, belongs to the 1-Cys subfamily of thiol-specific antioxidants (peroxiredoxins). The 28 kD protein contains a single cysteine residue at the position 46 which accounts for the antioxidant activity. Here we studied the effects of N-ethyilmaleimide and t-butyl hydroperoxide on the antioxidant activity of the 28 kD protein and that of the 23 kD protein from rat erythrocyte which is a member of 2-Cys subfamily of peroxiredoxines. N-ethylmaleimide, modifier for cysteine residues, had no effect on antioxidant activity of the dithiothreitol-treated 28 kD protein but irreversibly inhibited activity of the 23 kD protein under reducing conditions. The 28 kD protein was sensitive to treatment with peroxides: t-butyl hydroperoxide at micromolar concentrations was shown to irreversibly inactivate 28 kD protein. In the presence of dithiothreitol, the lower level of peroxide concentrations was required to inhibit 28 kD protein activity. The mechanism of this effect may be mediated through conversion of sulfhydryl group of 46Cys to oxidized states (46Cys-SO2H and 46Cys-SO3H). Antioxidant property of 23 kD protein was impaired by t-butyl hydroperoxide only in the presence of dithiothreitol. The concentrations of t-butyl hydroperoxide needed to affect the 23 kD protein were at least one order of magnitude higher than were required for the 28 kD protein inhibition. The given results suggest the essential differences between catalytic site of 28 kD protein and that of 2-Cys peroxiredoxins.