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

Kinetics of ferric Mycobacterium leprae truncated hemoglobin O (trHbO-Fe(III)) oxidation by H2O2 and of trHbO-Fe(IV)=O reduction by (NO)-N-center dot and NO2- are reported. The value of the second-order rate constant for H2O2-mediated oxidation of trHbO-Fe(III) is 2.4 x 10(3) M-1 s(-1). The value of the second-order rate constant for (NO)-N-center dot-mediated reduction of trHbO-Fe(IV)=O is 7.8 x 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 x 10(6) s(-1). The value of the second-order rate constant for NO2--mediated reduction of trHbO-Fe(IV)=O is 3.1 x 10(3) M-1 s(-1). As a whole, trHbO-Fe(IV)=O, generated upon reaction with H2O2, catalyzes (NO)-N-center dot reduction to NO2-. In turn, (NO)-N-center dot and NO2- 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 H2O2 and (NO)-N-center dot scavenging, protecting from nitrosative and oxidative stress, and sustaining mycobacterial respiration. (C) 2008 Elsevier Inc. All rights reserved.