Peroxynitrite scavenging by ferrous truncated hemoglobin GlbO from Mycobacterium leprae

Mycobacterium leprae GlbO has been proposed to represent merging of both O₂ uptake/transport and scavenging of nitrogen reactive species. Peroxynitrite reacts with M. leprae GlbO(II)-NO leading to GlbO(III) via the GlbO(III)-NO species. The value of the second order rate constant for GlbO(III)-NO formation is >1 × 10⁸ M^-1 s^-1 in the absence and presence of CO₂ (1.2 × 10^-3 M). The CO₂-independent value of the first order rate constant for GlbO(III)-NO denitrosylation is (2.5 ± 0.4) × 10¹ s^-1. Furthermore, peroxynitrite reacts with GlbO(II)-O₂ leading to GlbO(III) via the GlbO(IV){double bond, long}O species. Values of the second order rate constant for GlbO(IV){double bond, long}O formation are (4.8 ± 0.5) × 10⁴ and (6.3 ± 0.7) × 10⁵ M^-1 s^-1 in the absence and presence of CO₂ (=1.2 × 10^-3 M), respectively. The value of the second order rate constant for the peroxynitrite-mediated GlbO(IV){double bond, long}O reduction (= (1.5 ± 0.2) × 10⁴ M^-1 s^-1) is CO₂-independent. These data argue for a role of GlbO in the defense of M. leprae against nitrosative stress.