Different oxidative pathways of isonicotinic acid hydrazide and its meta-isomer, nicotinic acid hydrazide

Isoniazid Oxidation by Mycobacterium tuberculosis KatG: A Role for Superoxide Which Correlates with Isoniazid Susceptibility

“…Others have suggested INH oxidation occurs via an oxyferrous form of KatG reminiscent of the cytochrome P 450 oxygenase intermediate . In this work, we define a role for superoxide in KatG-mediated INH oxidation, a hypothesis predicated on reports of superoxide generation during INH oxidation by horseradish peroxidase, myeloperoxidase, and extracts of Mtb H37Ra. − We also demonstrate that KatG(S315T) exhibits reduced superoxide-dependent INH oxidation rates. In contrast, INH oxidation occurring via peroxidative routes does not correlate with INH resistance conferred by the S315T mutation.…”

“…A question arises as to the origin of superoxide in solutions containing only KatG and INH. Trace metals can catalyze oxidation of hydrazines by dioxygen generating superoxide, and superoxide is formed following trace metal-catalyzed autoxidation of INH at alkaline pH. ,, Addition of EDTA to KatG plus INH substantially reduced the INH oxidation rate. Alternatively, addition of both EDTA and xanthine/xanthine oxidase to KatG plus INH restored oxidation.…”

Correlation between Isoniazid Resistance and Superoxide Reactivity in Mycobacterium tuberculosis KatG

“…Oxidation of INH by KatG in the presence of air has been previously reported, with implications that such chemistry is mediated through an oxyferrous form of KatG. Several mechanisms exist for the spontaneous formation of oxyferrous KatG in solution, which has been previously shown to be a catalytically competent intermediate involved in the oxidation of INH: (i) trace N 2 H 4 present in solutions containing INH was suggested to lead to KatG reduction, followed by dioxygen binding yielding an oxyferrous intermediate capable of oxidizing INH; , (ii) trace metals have been implicated in superoxide formation, either through oxidation of hydrazines in the presence of dioxygen or via trace-metal catalyzed autoxidation of INH at alkaline pH; − (iii) the NADH-oxidase activity of KatG (from Burkholderia pseudomallei ) was also suggested to generate (in a pH-dependent reaction) either superoxide and/or hydrogen peroxide . Generation of superoxide may lead to the catalytically competent oxyferrous KatG. , Hydrogen peroxide, generated either indirectly by the spontaneous disproportionation of superoxide in solution or directly by the NADH-oxidase activity, at low levels (i.e., substoichiometric concentrations which are not subject to the catalase activity of KatG) would presumably form compound I, an intermediate known to promote the formation of the INH−NADH adduct (see below).…”

Isoniazid‐resistance conferring mutations inMycobacterium tuberculosisKatG: Catalase, peroxidase, and INH‐NADH adduct formation activities

“…Formation of Compound I may occur upon reaction with hydrogen peroxide, itself generated by either the spontaneous disproportionation of superoxide in solution,47 or by the NADH‐oxidase activity of KatG 23. Pathways for the spontaneous formation of oxyferrous KatG in solution include: (i) reduction of ferric (resting) KatG to the ferrous state by trace N 2 H 4 present in solutions containing INH, followed by dioxygen binding26, 27; (ii) trace metal catalyzed oxidation of hydrazines in the presence of dioxygen; (iii) trace metal catalyzed autoxidation of INH at alkaline pH48–50; and/or (iv) the pH‐dependent generation of superoxide or hydrogen peroxide via the NADH‐oxidase activity of KatG (as observed for Burkholderia pseudomallei ) 23. In the absence of KatG, the formation of the INH‐NADH adduct is undetectable under these conditions, highlighting the necessity of the enzyme for this reaction.…”