H2O2 and (.)NO scavenging by Mycobacterium leprae truncated hemoglobin O

Kinetics of ferric Mycobacterium leprae truncated hemoglobin O (trHbOFe(III)) oxidation by H2O2 and of trHbOFe(IV)O reduction by (.)NO and NO2- are reported. The value of the second-order rate constant for H2O2-mediated oxidation of trHbOFe(III) is 2.4 x 10(3) M(-1) s(-1). The value of the second-order rate constant for (.)NO-mediated reduction of trHbOFe(IV)O is 7.8 x 10(6) M(-1) s(-1). The value of the first-order rate constant for trHbOFe(III)ONO decay to the resting form trHbOFe(III) is 2.1 x 10(1) s(-1). The value of the second-order rate constant for NO2--mediated reduction of trHbOFe(IV)=O is 3.1 x 10(3) M(-1) s(-1). As a whole, trHbOFe(IV)O, generated upon reaction with H2O2, catalyzes (.)NO reduction to NO2-. In turn, (.)NO and NO2- act as antioxidants of trHbOFe(IV)O, which could be responsible for the oxidative damage of the mycobacterium. Therefore, Mycobacterium leprae trHbO could be involved in both H2O2 and (.)NO scavenging, protecting from nitrosative and oxidative stress, and sustaining mycobacterial respiration.