PROPERTIES OF CATALYTIC SITE OF 28 KD PROTEIN (1-CYS PEROXIREDOXIN) FROM RAT OLFACTORY EPITHELIUM

The secretory 28 kD protein, an abundant water-soluble protein from ra t olfactory epithelium, belongs to the 1-Cys subfamily of thiol-specif ic antioxidants (peroxiredoxins). The 28 kD protein contains a single cystein residue at; the position 46 which accounts for the antioxidant activity. Here we studied the effects of N-ethilmaleimide and t-butil hydroperoxide on the antioxidant: activity of the 28 kD protein and t hat of the 23 kD protein from rat erythrocyte which. is a member of 2- Cys subfamily of peroxiredoxines. N-ethilmaleimide, modificator for cy stein residues, had no effect on antioxidant: activity of the dithioth reitol-treated 28 kD protein but irreversibly inhibited activity of th e 23 kD protein under reducing conditions. The 28 kD protein was sensi tive to treatment with peroxides: t-butyI hydroperoxide at micromolar concentrations was shown to irreversibly inactivate 28 kD protein. In the presence of dithiothreitol, the lower level of peroxide concentrat ions was required to inhibit 28 kD protein activity. The mechanism of this effect may be mediated through conversion of sulfhydril group of 46Cys to oxidazed states (46Cys-SO2N: and 46Cys-SO3H). Antioxidant pro perty of 23 kD protein was impaired by t-butyl hydroperoxide only in t he presence of dithiothreitol. The concentrations of t-butyl hydropero xide needed to affect the 23 kD protein were at least one order of mag nitude higher than were required for the 28 kD protein inhibition. The given results suggest the essential differences between catalytic sit e of 28 kD protein and that of 2-Cys peroxiredoxines.