Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.11.1.7 (peroxidase)
 65,474 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Peroxidase from Mycobacterium tuberculosis H37Rv was purified to homogeneity. The homogeneous protein exhibits catalase and Y (Youatt's)-enzyme activities in addition to peroxidase activity. Further confirmation that the three activities are due to a single enzyme was accomplished by other criteria, such as differential thermal inactivation, sensitivity to different inhibitors, and co-purification. The Y enzyme (peroxidase) was separated from NADase (NAD+ glycohydrolase) inhibitor by gel filtration on Sephadex G-200. The molecular weights of peroxidase and NADase inhibitor, as determined by gel filtration, are 240000 and 98000 respectively. The Y enzyme shows two Km values for both isoniazid (isonicotinic acid hydrazide) and NAD at low and high concentrations. Analysis of the data by Hill plots revealed that the enzyme has one binding site at lower substrate concentrations and more than one at higher substrate concentration. The enzyme contains 6g-atoms of iron/mol. Highly purified preparations of peroxidases from different sources catalyse the Y-enzyme reaction, suggesting that the nature of the reaction may be a peroxidatic oxidation of isoniazid. Moreover, the Y-enzyme reaction is enhanced by O2. Isoniazid-resistant mutants do not exhibit Y-enzyme, peroxidase or catalase activities, and do not take up isoniazid. The Y-enzyme reaction is therefore implicated in the uptake of the drug.
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PMID:The purification and properties of peroxidase in Mycobacterium tuberculosis H37Rv and its possible role in the mechanism of action of isonicotinic acid hydrazide. 24 21

The tuberculostatic agent isoniazid has been implicated in inducing various idiosyncratic reactions including drug-induced lupus. The mechanism is unknown but may involve a reactive metabolite of the drug. Isoniazid was oxidized by activated leukocytes to isonicotinic acid. Myeloperoxidase is likely the enzyme in the leukocyte involved, since the oxidation was inhibited by azide, which inhibits myeloperoxidase, and by catalase, which catalyzes the breakdown of hydrogen peroxide. The same metabolic profile was observed when isoniazid was incubated with purified myeloperoxidase and hydrogen peroxide. The rate of the reaction was increased in the presence of chloride. Hypochlorous acid was also able to oxidize isoniazid to isonicotinic acid. Isoniazid, or an oxidative product, inhibited the reaction when high initial substrate concentrations were used. Isoniazid is oxidized by activated leukocytes, possibly to a reactive intermediate, which may have implications for isoniazid-induced lupus.
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PMID:Metabolism of isoniazid by activated leukocytes. Possible role in drug-induced lupus. 135 11

The effect of five antimycobacterial drugs isoniazid, rifampicin, streptomycin, pyrazinamide and ethambutol on the generation of reactive oxidants by polymorphonuclear leucocytes was investigated in vitro, using N-formyl-L-methionyl-L-leucyl-phenylalanine (FMLP) activated and spontaneous luminol-enhanced chemiluminescence and myeloperoxidase-mediated iodination. Streptomycin, pyrazinamide and ethambutol had no effect on the assays at the concentrations investigated. Isoniazid as concentrations of 1.25 and 5 micrograms/ml and rifampicin at 100 micrograms/ml significantly inhibited iodination. Rifampicin also caused dose-dependent inhibition of chemiluminescence which was partly due to its light-absorbing activities. It is concluded that isoniazid, and to a lesser extent, rifampicin at therapeutic concentrations possess anti-oxidative properties.
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PMID:Antimycobacterial drugs and the production of reactive oxidants by polymorphonuclear leucocytes in vitro. 283 29

Isoniazid (INH) induced mitotic gene conversion at the trp5 locus of strain D7 of Saccharomyces cerevisiae. A suggested mechanism involving autoxidation of INH and production of hydrogen peroxide is supported by the facts that (i) the presence of a transition metal, Mn(II), greatly enhanced the effect of INH, (ii) cells stored for a long time in the refrigerator are much more sensitive to INH + Mn(II) than fresh cells probably due to loss of catalase and/or peroxidase activity, (iii) presence of S9 mix during the treatment eliminated the effect of INH + Mn(II).
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PMID:Mitotic gene conversion induced in yeast by isoniazid. influence of a transition metal and of the physiological conditions of the cells. 701 99

Isoniazid resistance in Mycobacterium tuberculosis has been associated with total deletion of the katG gene, which codes for catalase-peroxidase production. To determine whether this is a common mechanism of drug resistance, 9 isolates of isoniazid-resistant and 1 of isoniazid-sensitive M. tuberculosis were analyzed by polymerase chain reaction amplification of a 237-bp sequence of the katG gene. Amplification was observed in the isoniazid-sensitive isolate and in 8 resistant isolates; in only 1 isoniazid-resistant isolate was there no amplification of the expected band, suggesting gene deletion. DNA sequencing showed that 8 of the 9 isolates had point mutations, deletions, or insertions of 1-3 bases. Evidence corroborating the presence of mutations in the katG gene was obtained by single-strand conformation polymorphism analysis in these 8 isolates. Thus, mutations as well as insertions and deletions in the katG gene can account for inactive catalase peroxidase, leading to isoniazid resistance; gene deletion occurs only infrequently, in approximately 11% of cases.
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PMID:Mutations in the catalase-peroxidase gene from isoniazid-resistant Mycobacterium tuberculosis isolates. 816 15

Isoniazid-resistant isolates of Mycobacterium tuberculosis were transformed with a plasmid vector carrying the functional catalase-peroxidase (katG) gene. Expression of katG restored full drug susceptibility in isolates initially resistant to concentrations ranging from 3.2 to > 50 micrograms ml-1. Transformation with the corresponding katG gene from Escherichia coli resulted in low-level expression of catalase and peroxidase activities and conferred partial isoniazid sensitivity.
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PMID:Transformation with katG restores isoniazid-sensitivity in Mycobacterium tuberculosis isolates resistant to a range of drug concentrations. 839 39

Isoniazid is the most widely used antituberculosis drug. Genetic studies in Mycobacterium smegmatis identified the inhA-encoded, NADH-dependent enoyl acyl carrier protein reductase as the primary target for this drug. A reactive form of isoniazid inhibits InhA by reacting with the NAD(H) cofactor bound to the enzyme active site forming a covalent adduct (isonicotinic acyl NADH) that is apt to bind with high affinity. Resistance can occur by increased expression of InhA or by mutations that lower the enzyme's affinity to NADH. Both of these resistance mechanisms are observed in 30% of clinical tuberculosis isolates. Mutation in katG, which encodes catalase peroxidase, is the most common source for resistance. Another mechanism for isoniazid resistance, in M. smegmatis, occurs by defects in NADH dehydrogenase (Ndh) of the respiratory chain. Genetic data indicated that ndh mutations confer resistance by lowering the rate of NADH oxidation and increasing the intracellular NADH/NAD+ ratio. An increased amount of NADH may prevent formation of isonicotinic acyl NADH or may promote displacement of the isonicotinic acyl NADH from InhA. While our studies have identified this mechanism in M. smegmatis, results reported in early literature lead us to believe that it can occur in Mycobacterium tuberculosis.
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PMID:Mechanisms for isoniazid action and resistance. 994 10

Resonance Raman spectra of native, overexpressed M. tuberculosis catalase-peroxidase (KatG), the enzyme responsible for activation of the antituberculosis antibiotic isoniazid (isonicotinic acid hydrazide), have confirmed that the heme iron in the resting (ferric) enzyme is high-spin five-coordinate. Difference Raman spectra did not reveal a change in coordination number upon binding of isoniazid to KatG. Stopped-flow spectrophotometric studies of the reaction of KatG with stoichiometric equivalents or small excesses of hydrogen peroxide revealed only the optical spectrum of the ferric enzyme with no hypervalent iron intermediates detected. Large excesses of hydrogen peroxide generated oxyferrous KatG, which was unstable and rapidly decayed to the ferric enzyme. Formation of a pseudo-stable intermediate sharing optical characteristics with the porphyrin pi-cation radical-ferryl iron species (Compound I) of horseradish peroxidase was observed upon reaction of KatG with excess 3-chloroperoxybenzoic acid, peroxyacetic acid, or tert-butylhydroperoxide (apparent second-order rate constants of 3.1 x 10(4), 1.2 x 10(4), and 25 M(-1) s(-1), respectively). Identification of the intermediate as KatG Compound I was confirmed using low-temperature electron paramagnetic resonance spectroscopy. Isoniazid, as well as ascorbate and potassium ferrocyanide, reduced KatG Compound I to the ferric enzyme without detectable formation of Compound II in stopped-flow measurements. This result differed from the reaction of horseradish peroxidase Compound I with isoniazid, during which Compound II was stably generated. These results demonstrate important mechanistic differences between a bacterial catalase-peroxidase and the homologous plant peroxidases and yeast cytochrome c peroxidase, in its reactions with peroxides as well as substrates.
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PMID:Catalase-peroxidase (Mycobacterium tuberculosis KatG) catalysis and isoniazid activation. 1093 18

KatG, the catalase peroxidase from Mycobacterium tuberculosis, is important in the activation of the antitubercular drug, isoniazid. About 50% of isoniazid-resistant clinical isolates contain a mutation in KatG wherein the serine at position 315 is substituted with threonine, KatG(S315T). The heme pockets of KatG and KatG(S315T) and their interactions with isoniazid are probed using resonance Raman (rR) spectroscopy to characterize their ferrous CO complexes. Three vibrational modes, C-O and Fe-C stretching and Fe-CO bending, are assigned using 12CO and 13CO isotope shifts. Two conformers are observed for KatG-CO and KatG(S315T)-CO. Resonance Raman features assigned to form I are consistent with it having a neutral proximal histidine ligand and the Fe-C-O moiety hydrogen bonded to a distal residue. The nu(C-O) band for form I is sharp, consistent with a conformationally homogeneous Fe-CO unit. Form II also has a neutral proximal histidine ligand but is not hydrogen bonded. This appears to result in a conformationally disordered Fe-CO unit, as evidenced by a comparatively broad C-O stretching band. The 13CO-sensitive bands assigned to form II are predominant in the KatG(S315T)-CO rR spectrum. Isoniazid binding is apparent from the resonance Raman signatures of both WT KatG-CO and KatG(S315T)-CO. Moreover, isoniazid binding elicits an increase in the form I population of wild-type KatG-CO while having little, if any, effect on the already low population of form I of KatG(S315T)-CO. Since oxyKatG (compound III) also contains a low-spin diatomic ligand-heme adduct (heme-O2), it is reasonable to suggest that it too would exist as a mixture of conformers. Because the small form I population of KatG(S315T)-CO correlates with its inability to activate INH, we hypothesize that form I plays a role in INH activation.
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PMID:Carbon monoxide adducts of KatG and KatG(S315T) as probes of the heme site and isoniazid binding. 1140 61

The antitubercular agent isoniazid can be activated by Mycobacterium tuberculosis KatG using either a peroxidase compound I/II or a superoxide-dependent oxyferrous pathway. The identity of activated isoniazid is unknown, but it has been suggested that it may be a free radical intermediate. In this work, EPR spin trapping experiments detected isoniazid-derived radicals generated during KatG-mediated oxidation via the peroxidase compound I/II pathway. On the basis of hyperfine splitting patterns and oxygen dependence, these radicals were identified as the acyl, acyl peroxo, and pyridyl radicals of isoniazid. Isoniazid-resistant KatG(S315T) produced the same radicals found with KatG, while the less potent antitubercular agent nicotinic acid hydrazide produced the corresponding nicotinyl radicals. The time course of radical production was similar for KatG and KatG(S315T), while a lower steady-state level of radicals was produced from nicotinic acid hydrazide. These results support an earlier finding that the peroxidase pathway does not correlate with isoniazid resistance conferred by KatG(S315T). Trace amounts of radicals were detected via the superoxide-dependent pathway. The low level of isoniazid-derived radicals found in the superoxide-dependent pathway may be due to scavenging by superoxide.
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PMID:Evidence for isoniazid-dependent free radical generation catalyzed by Mycobacterium tuberculosis KatG and the isoniazid-resistant mutant KatG(S315T). 1146 61


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