The one-electron reduction potentials of NAD

Farrington, John A.; Land, Edward J.; Swallow, A. J.

doi:10.1016/0005-2728(80)90031-6

Cited by 70 publications

(34 citation statements)

References 10 publications

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“…The proposed scheme in Fig. 2 (48). When the basal system is perturbed to allow some IN⅐NAD synthesis in the presence of SOD, other radical species must replace O 2 .…”

Section: Discussionmentioning

confidence: 99%

Isonicotinic Acid Hydrazide Conversion to Isonicotinyl-NAD by Catalase-peroxidases

Wiseman

Carpena

Feliz

et al. 2010

Journal of Biological Chemistry

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Activation of the pro-drug isoniazid (INH) as an anti-tubercular drug in Mycobacterium tuberculosis Isonicotinic acid hydrazide (isoniazid or INH)3 is a widely used anti-tubercular pro-drug that requires activation in a reaction involving the catalase-peroxidase KatG of Mycobacterium tuberculosis (MtKatG) (1) whereby the hydrazine group is removed and the isonicotinyl portion is added to NAD ϩ to generate isonicotinyl-NAD or IN⅐NAD (see Fig. 1). Once formed, IN⅐NAD inhibits the synthesis of mycolic acids, and therefore, the growth of M. tuberculosis, by binding to the longchain enoyl acyl carrier protein reductase (InhA) (2). Despite understanding the role of IN⅐NAD in the inhibition of mycolic acid synthesis and knowing that KatG is required for INH activation in vivo, uncertainties about the mechanism of its formation remain.The involvement of MtKatG in INH activation suggested that the peroxidatic process had a role, and this provided a focus for several studies employing external oxidants such as peroxyacetic acid (3), t-butyl hydroperoxide (4 -6) and low levels of H 2 O 2 (7, 6) to activate the peroxidatic pathway for INH oxidation and activation. In addition, EPR studies have demonstrated that INH can serve as an electron source to reduce peroxidatic intermediates, including specific Trp ⅐ radical species following peroxyacetic acid oxidation of MtKatG (3,8).A multiplicity of methods has been employed to directly and indirectly assay INH activation, including the determination of INH oxidation to isonicotinic acid (9, 10), the HPLC assay of INH disappearance (11), the inactivation of InhA in a mixture of InhA and KatG (7,12,13,14), the HPLC detection of IN⅐NAD (4, 15), and the direct measurement of IN⅐NAD using its characteristic absorbance at 326 nm (6,7,12,15,16). Reports of INH activation in mixtures lacking an external oxidant (4,5,6,9,12,14,15) initially suggested that the peroxidatic process may not be required, but the mixtures of INH, NADH, and KatG would have supported NADH reduction of molecular oxygen to superoxide and low levels of H 2 O 2 (15) to activate the peroxidase reaction.Despite the considerable evidence that a peroxidatic process is involved in IN⅐NAD synthesis, attempts to rationalize the reaction entirely in terms of the peroxidatic pathway generally produced models that were incomplete from the standpoint of electron balance (5,7,10) or that involved hypothetical intermediates not characterized in any other system (5, 6). For example, a common scheme shows the isonicotinyl radical, generated in a peroxidatic reaction, reacting with NAD ϩ to yield IN⅐NAD, when such a reaction would actually yield the IN⅐NAD ϩ ⅐ radical (Fig. 1). The need to reduce this radical in an oxidizing environment suggests that more than a simple peroxidatic pathway is involved in the INH activation process. This rationale leads to superoxide, O 2. , a known reducing agent with

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“…The proposed scheme in Fig. 2 (48). When the basal system is perturbed to allow some IN⅐NAD synthesis in the presence of SOD, other radical species must replace O 2 .…”

Section: Discussionmentioning

confidence: 99%

Isonicotinic Acid Hydrazide Conversion to Isonicotinyl-NAD by Catalase-peroxidases

Wiseman

Carpena

Feliz

et al. 2010

Journal of Biological Chemistry

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“…The MPO\H # O # system catalysed the one-electron oxidation of tyrosine to tyrosyl radical which, in turn, rapidly oxidized NADPH (Scheme 1). Transient tyrosyl radicals are known to oxidize pyridine nucleotides by a direct one-electron transfer process [k l (6-8)i10( M −" :s −" ] [41], which results in the formation of NAD(P)d radical, a potent reductant [E m,( of NAD(P) + \NAD(P)d l k920 mV] [42]. Subsequently, the nucleotide radical is capable of rapidly reducing molecular oxygen (k l 2i10* M −" :s −" ) [ In contrast, results presented here on the guaiacolmediated NADPH oxidation suggest that a radical did not react with NADPH.…”

Section: Discussionmentioning

confidence: 99%

Oxidation of guaiacol by myeloperoxidase: a two-electron-oxidized guaiacol transient species as a mediator of NADPH oxidation

Capeillère‐Blandin

1998

Biochemical Journal

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The present study was first aimed at a complete steady-state kinetic analysis of the reaction between guaiacol (2-methoxyphenol) and the myeloperoxidase (MPO)/H2O2 system, including a description of the isolation and purification of MPO from human polymorphonuclear neutrophil cells. Secondly, the overall reaction of the oxidation of NADPH, mediated by the reactive intermediates formed from the oxidation of guaiacol in the MPO/H2O2 system, was analysed kinetically. The presence of guaiacol stimulates the oxidation of NADPH by the MPO/H2O2 system in a concentration-dependent manner. Concomitantly, the accumulation of biphenoquinone (BQ), the final steady-state product of guaiacol oxidation, is lowered, and even inhibited completely, at high concentrations of NADPH. Under these conditions, the stoichiometry of NADPH:H2O2 is 1, and the oxidation rate of NADPH approximates to that of the rate of guaiacol oxidation by MPO. The effects of the presence of superoxide dismutase, catalase and of anaerobic conditions on the overall oxidation of NADPH have also been examined, and the data indicated that superoxide formation did not occur. The final product of NADPH oxidation was shown to be enzymically active NADP+, while guaiacol was generated continuously from the reaction between NADPH and oxidized guaiacol product. In contrast, similar experiments performed on the indirect, tyrosine-mediated oxidation of NADPH by MPO showed that a propagation of the free radical chain was occurring, with generation of both O2(-.) and H2O2. BQ, in itself, was able to spontaneously oxidize NADPH, but neither the rate nor the stoichiometry of the reaction could account for the NADPH-oxidation process involved in the steady-state peroxidation cycle. These results provide evidence that the oxidation of NADPH does not involve a free nucleotide radical intermediate, but that this is probably due to a direct electron-transfer reaction between NADPH and a two-electron-oxidized guaiacol intermediate.

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“…Indeed, the semiquinone flavin intermediate state need not even be entirely stable, as long as stability product (product of the NADH and flavin stability constants) is no smaller than 10 ñ20 , to achieve the millisecond rates often observed for these proteins. Using the reported aqueous NAD/NAD + redox couple of ñ0.92V (Farrington et al, 1980), we estimate an aqueous stability constant of NAD + /NADH of about 10 ñ20 . Thus, even a small amount of stabilization of the NAD radical intermediate by the protein will permit unstable flavin radical intermediates to be used.…”

Section: Cluster Examplesmentioning

confidence: 99%