title: *NO dissociation represents the rate limiting step for O2-mediated oxidation of ferrous nitrosylated Mycobacterium leprae truncated hemoglobin O.
abstract: 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 O(2)-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 (k(off)) and of the first-order rate constant for O(2)-mediated oxidation of M. leprae trHbO(II)-NO (h) are 1.3 x 10(-4) s(-1) and 1.2 x 10(-4) s(-1), respectively. The coincidence of values of k(off) and h suggests that O(2)-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 O(2) but may stay trapped in a protein cavity(ies) close to heme(II). Next, M. leprae trHbO(II)-O(2) 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 O(2)-mediated oxidation of M. leprae trHbO(II)-NO.
authors: Department of Biology and Interdepartmental Laboratory for Electron Microscopy, University Roma Tre, Viale Guglielmo Marconi 446, I-00146 Roma, Italy. ascenzi@bio.uniroma3.it
authors: Paolo
authors: P
authors: Ascenzi
authors: Martino
authors: M
authors: Bolognesi
authors: Paolo
authors: P
authors: Visca
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D002248:Carbon Monoxide / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D006418:Heme / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics; D007700:Kinetics; D008956:Models, Chemical; D009569:Nitric Oxide / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D054793:Truncated Hemoglobins
chemical_list: D001426:Bacterial Proteins; D005296:Ferrous Compounds; D006454:Hemoglobins; D011994:Recombinant Proteins; D054793:Truncated Hemoglobins; C460871:truncated hemoglobin, Mycobacterium leprae; D009569:Nitric Oxide; D006418:Heme; D002248:Carbon Monoxide; D010100:Oxygen