H 2O 2 and [rad]NO scavenging by Mycobacterium leprae truncated hemoglobin O

Abstract

Kinetics of ferric Mycobacterium leprae truncated hemoglobin O (trHbO Fe(III)) oxidation by H 2O 2 and of trHbO Fe(IV) O reduction by NO and NO 2 − are reported. The value of the second-order rate constant for H 2O 2-mediated oxidation of trHbO Fe(III) is 2.4 × 10 3 M −1 s −1. The value of the second-order rate constant for NO-mediated reduction of trHbO Fe(IV) O is 7.8 × 10 6 M −1 s −1. The value of the first-order rate constant for trHbO Fe(III) ONO decay to the resting form trHbO Fe(III) is 2.1 × 10 1 s −1. The value of the second-order rate constant for NO 2 −-mediated reduction of trHbO Fe(IV) O is 3.1 × 10 3 M −1 s −1. As a whole, trHbO Fe(IV) O, generated upon reaction with H 2O 2, catalyzes NO reduction to NO 2 −. In turn, NO and NO 2 − act as antioxidants of trHbO Fe(IV) O, which could be responsible for the oxidative damage of the mycobacterium. Therefore, Mycobacterium leprae trHbO could be involved in both H 2O 2 and NO scavenging, protecting from nitrosative and oxidative stress, and sustaining mycobacterial respiration.