H₂O₂ and ^{{radical dot}}NO scavenging by Mycobacterium leprae truncated hemoglobin O

Kinetics of ferric Mycobacterium leprae truncated hemoglobin O (trHbO{single bond}Fe(III)) oxidation by H₂O₂ and of trHbO{single bond}Fe(IV){double bond, long}O reduction by ^{{radical dot}}NO and NO₂ ^- are reported. The value of the second-order rate constant for H₂O₂-mediated oxidation of trHbO{single bond}Fe(III) is 2.4 × 10³ M^-1 s^-1. The value of the second-order rate constant for ^{{radical dot}}NO-mediated reduction of trHbO{single bond}Fe(IV){double bond, long}O is 7.8 × 10⁶ M^-1 s^-1. The value of the first-order rate constant for trHbO{single bond}Fe(III){single bond}ONO decay to the resting form trHbO{single bond}Fe(III) is 2.1 × 10¹ s^-1. The value of the second-order rate constant for NO₂ ^--mediated reduction of trHbO{single bond}Fe(IV){double bond, long}O is 3.1 × 10³ M^-1 s^-1. As a whole, trHbO{single bond}Fe(IV){double bond, long}O, generated upon reaction with H₂O₂, catalyzes ^{{radical dot}}NO reduction to NO₂ ^-. In turn, ^{{radical dot}}NO and NO₂ ^- act as antioxidants of trHbO{single bond}Fe(IV){double bond, long}O, which could be responsible for the oxidative damage of the mycobacterium. Therefore, Mycobacterium leprae trHbO could be involved in both H₂O₂ and ^{{radical dot}}NO scavenging, protecting from nitrosative and oxidative stress, and sustaining mycobacterial respiration.