Nitrite-Reductase and Peroxynitrite Isomerization Activities of Methanosarcina acetivorans Protoglobin

摘要: Within the globin superfamily, protoglobins (Pgb) belong phylogenetically to same cluster of two-domain globin-coupled sensors and single-domain sensor globins. Multiple functional roles have been postulated for Methanosarcina acetivorans Pgb (Ma-Pgb), since detoxification reactive nitrogen oxygen species might co-exist with enzymatic activity(ies) facilitate conversion CO methane. Here, nitrite-reductase peroxynitrite isomerization activities CysE20Ser mutant Ma-Pgb (Ma-Pgb*) are reported analyzed in parallel those related heme-proteins. Kinetics activity ferrous Ma-Pgb* (Ma-Pgb*-Fe(II)) is biphasic values second-order rate constant reduction NO2– NO concomitant formation nitrosylated Ma-Pgb*-Fe(II) (Ma-Pgb*-Fe(II)-NO) kapp1 = 9.6±0.2 M–1 s–1 kapp2 = 1.2±0.1 (at pH 7.4 20°C). The kapp1 kapp2 increase by about one order magnitude each unit decrease, between 8.3 6.2, indicating that reaction requires proton. On other hand, kinetics catalyzed ferric (Ma-Pgb*-Fe(III)) monophasic second Ma-Pgb*-Fe(III) first spontaneous nitrate happ = 3.8×104 h0 = 2.8×10–1 pH-dependence hon h0 reflects acid-base equilibrium (pKa = 6.7 6.9, respectively; at 20°C), HOONO reacts preferentially heme-Fe(III) atom. These results highlight potential role Pgbs biosynthesis scavenging species.