NO dissociation represents the rate limiting step for O2-mediated oxidation of ferrous nitrosylated Mycobacterium leprae truncated hemoglobin O

Mycobacterium leprae truncated hemoglobin O (trHbO) protects from nitrosative stress and sustains mycobacterial respiration. Here, kinetics of M. leprae trHbO(II)-NO denitrosylation and of O2-mediated oxidation of M. leprae trHbO(II)-NO are reported. Values of the first-order rate constant for NO dissociation from M. leprae trHbO(II)-NO (koff) and of the first-order rate constant for O2-mediated oxidation of M. leprae trHbO(II)-NO (h) are 1.3 × 10−4 s−1 and 1.2 × 10−4 s−1, respectively. The coincidence of values of koff and h suggests that O2-mediated oxidation of M. leprae trHbO(II)-NO occurs with a reaction mechanism in which NO, that is initially bound to heme(II), is displaced by O2 but may stay trapped in a protein cavity(ies) close to heme(II). Next, M. leprae trHbO(II)-O2 reacts with NO giving the transient Fe(III)-OONO species preceding the formation of the final product M. leprae trHbO(III). NO dissociation from heme(II)-NO represents the rate limiting step for O2-mediated oxidation of M. leprae trHbO(II)-NO.