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Black SR, Fennell TR, Mathews JM, Snyder RW, Patel PR, Watson SL, Sutherland V, Waidyanatha S. Disposition of [ 14C]hydroquinone in Harlan Sprague-Dawley rats and B6C3F1/N mice: species and route comparison. Xenobiotica 2017; 48:1128-1141. [PMID: 29166815 DOI: 10.1080/00498254.2017.1398847] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
1. Hydroquinone (HQ) is present in some foods and has varied industrial, medical and consumer uses. These studies were undertaken to investigate the disposition of HQ in rats and mice following gavage, intravenous (IV) and dermal exposure. 2. [14 C]HQ administered (0.5, 5 or 50 mg/kg) by gavage or IV routes to male and female Harlan Sprague-Dawley (HSD) rats and B6C3F1/N mice was well absorbed and rapidly excreted primarily in urine. Radioactivity remaining in tissues at 72 h was <1% for both species at all dose levels and routes. No sex, species or route related differences in disposition were found. 3. With dermal application of 2, 10 or 20% [14 C]HQ, mice absorbed higher percentages of the dose than rats (37, 12, 12% versus 18.6, 4.43 and 1.79%, respectively). The HQ mass absorbed by mice increased with dose, while in rats it was more constant over the dose range. Absorbed HQ was rapidly excreted in urine of both species and urinary excretion indicated continued absorption over the exposure period. No sex differences in disposition were found. 4. The oral bioavailability of HQ at 5 mg/kg was low in both rats (1.6%) and mice (3.9%) demonstrating significant first pass metabolism. Dermal bioavailability in mice was 9.4% following application of 2% formulation. 5. Urinary metabolites for both species and all routes included the glucuronide and sulfate conjugates; no parent was found in urine.
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Affiliation(s)
- Sherry R Black
- a Discovery Sciences, RTI International , Research Triangle Park , NC , USA and
| | - Timothy R Fennell
- a Discovery Sciences, RTI International , Research Triangle Park , NC , USA and
| | - James M Mathews
- a Discovery Sciences, RTI International , Research Triangle Park , NC , USA and
| | - Rodney W Snyder
- a Discovery Sciences, RTI International , Research Triangle Park , NC , USA and
| | - Purvi R Patel
- a Discovery Sciences, RTI International , Research Triangle Park , NC , USA and
| | - Scott L Watson
- a Discovery Sciences, RTI International , Research Triangle Park , NC , USA and
| | - Vicki Sutherland
- b Division of the National Toxicology Program, National Institute of Environmental Health Sciences (NIEHS) , Research Triangle Park , NC , USA
| | - Suramya Waidyanatha
- b Division of the National Toxicology Program, National Institute of Environmental Health Sciences (NIEHS) , Research Triangle Park , NC , USA
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Prevalence of iodine inadequacy in Switzerland assessed by the estimated average requirement cut-point method in relation to the impact of iodized salt. Public Health Nutr 2014; 18:1333-42. [PMID: 25231207 DOI: 10.1017/s1368980014002018] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
OBJECTIVE To assess the iodine status of Swiss population groups and to evaluate the influence of iodized salt as a vector for iodine fortification. DESIGN The relationship between 24 h urinary iodine and Na excretions was assessed in the general population after correcting for confounders. Single-day intakes were estimated assuming that 92 % of dietary iodine was excreted in 24 h urine. Usual intake distributions were derived for male and female population groups after adjustment for within-subject variability. The estimated average requirement (EAR) cut-point method was applied as guidance to assess the inadequacy of the iodine supply. SETTING Public health strategies to reduce the dietary salt intake in the general population may affect its iodine supply. SUBJECTS The study population (1481 volunteers, aged ≥15 years) was randomly selected from three different linguistic regions of Switzerland. RESULTS The 24 h urine samples from 1420 participants were determined to be properly collected. Mean iodine intakes obtained for men (n 705) and women (n 715) were 179 (sd 68.1) µg/d and 138 (sd 57.8) µg/d, respectively. Urinary Na and Ca, and BMI were significantly and positively associated with higher iodine intake, as were men and non-smokers. Fifty-four per cent of the total iodine intake originated from iodized salt. The prevalence of inadequate iodine intake as estimated by the EAR cut-point method was 2 % for men and 14 % for women. CONCLUSIONS The estimated prevalence of inadequate iodine intake was within the optimal target range of 2-3 % for men, but not for women.
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Nepravishta R, Sabelli R, Iorio E, Micheli L, Paci M, Melino S. Oxidative species and S-glutathionyl conjugates in the apoptosis induction by allyl thiosulfate. FEBS J 2011; 279:154-67. [DOI: 10.1111/j.1742-4658.2011.08407.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Kudugunti SK, Vad NM, Whiteside AJ, Naik BU, Yusuf MA, Srivenugopal KS, Moridani MY. Biochemical mechanism of caffeic acid phenylethyl ester (CAPE) selective toxicity towards melanoma cell lines. Chem Biol Interact 2010; 188:1-14. [PMID: 20685355 DOI: 10.1016/j.cbi.2010.05.018] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Revised: 05/27/2010] [Accepted: 05/27/2010] [Indexed: 11/30/2022]
Abstract
In the current work, we investigated the in vitro biochemical mechanism of Caffeic Acid Phenylethyl Ester (CAPE) toxicity and eight hydroxycinnamic/caffeic acid derivatives in vitro, using tyrosinase enzyme as a molecular target in human SK-MEL-28 melanoma cells. Enzymatic reaction models using tyrosinase/O(2) and HRP/H(2)O(2) were used to delineate the role of one- and two-electron oxidation. Ascorbic acid (AA), NADH and GSH depletion were used as markers of quinone formation and oxidative stress in CAPE induced toxicity in melanoma cells. Ethylenediamine, an o-quinone trap, prevented the formation of o-quinone and oxidations of AA and NADH mediated by tyrosinase bioactivation of CAPE. The IC(50) of CAPE towards SK-MEL-28 melanoma cells was 15muM. Dicoumarol, a diaphorase inhibitor, and 1-bromoheptane, a GSH depleting agent, increased CAPE's toxicity towards SK-MEL-28 cells indicating quinone formation played an important role in CAPE induced cell toxicity. Cyclosporin-A and trifluoperazine, inhibitors of the mitochondrial membrane permeability transition pore (PTP), prevented CAPE toxicity towards melanoma cells. We further investigated the role of tyrosinase in CAPE toxicity in the presence of a shRNA plasmid, targeting tyrosinase mRNA. Results from tyrosinase shRNA experiments showed that CAPE led to negligible anti-proliferative effect, apoptotic cell death and ROS formation in shRNA plasmid treated cells. Furthermore, it was also found that CAPE selectively caused escalation in the ROS formation and intracellular GSH (ICG) depletion in melanocytic human SK-MEL-28 cells which express functional tyrosinase. In contrast, CAPE did not lead to ROS formation and ICG depletion in amelanotic C32 melanoma cells, which do not express functional tyrosinase. These findings suggest that tyrosinase plays a major role in CAPE's selective toxicity towards melanocytic melanoma cell lines. Our findings suggest that the mechanisms of CAPE toxicity in SK-MEL-28 melanoma cells mediated by tyrosinase bioactivation of CAPE included quinone formation, ROS formation, intracellular GSH depletion and induced mitochondrial toxicity.
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Affiliation(s)
- Shashi K Kudugunti
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, TX 79106, USA
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Almeida LE, Imasato H, Tabak M. Enzymatic oxidation of dipyridamole in homogeneous and micellar solutions in the horseradish peroxidase–hydrogen peroxide system. Biochim Biophys Acta Gen Subj 2006; 1760:216-26. [PMID: 16310957 DOI: 10.1016/j.bbagen.2005.10.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2005] [Revised: 09/16/2005] [Accepted: 10/07/2005] [Indexed: 11/28/2022]
Abstract
Enzymatic oxidation of dipyridamole (DIP) by horseradish peroxidase-hydrogen peroxide system (HRP-H2O2) in aqueous and micellar solutions was carried out. The reaction was monitored by optical absorption and fluorescence techniques. In aqueous solution at pH 7.0 and pH 9.0, the disappearance of the characteristic bands of DIP centered at 400 nm and 280 nm was observed. A new strong band at 260 nm is observed for the oxidation product(s) with shoulders at 322 nm and 390 nm. A non-fluorescent product is formed upon oxidation. In cationic cethyl trimethyl-1-ammonium chloride (CTAC) and zwitterionic 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS) micellar solutions the same results are observed: three, well-defined, isosbestic points in the optical spectra suggest the transformation between two species. In anionic micellar sodium dodecylsulfate solution (SDS), the appearance of a new band centered around 506 nm was observed, associated to a solution color change from the usual yellow to deep blue/violet, characteristic of a radical species associated to the one-electron oxidation of DIP to its cation radical (DIP*+), observed previously in electrochemical oxidation. Experiments of radical decay kinetics monitoring the absorbance change at 506 nm were performed and analyzed in the frame of a kinetic model taking into account the species both in homogeneous and micellar media. The reaction medium is composed of bulk solution, SDS micelle/solution interface and enzyme catalytic site(s). The variation of DIP*+ concentration was analyzed assuming: (1) synthesis of DIP*+ by HRP through one-electron oxidation; (2) decomposition of DIP*+ by further one-electron oxidation; (3) direct two-electron oxidation of DIP by HRP; (4) bimolecular DIP*+ disproportionation. The main results of the analysis are as follows: (1) kinetic data can be divided in two phases, an HRP active phase and another phase which proceeds in the absence of enzyme activity due to consumption of all H2O2; (2) the reactions of DIP*+ formation, DIP*+ decomposition and DIP two-electron oxidation are HRP concentration dependent; (3) since DIP*+ formation constant seems to be overestimated, it is proposed that two-electron oxidation is another source of DIP*+, through the comproportionation reaction. Evidences for this reaction were also observed previously in electrochemical experiments; and (4) the kinetic analysis provides evidences that the bimolecular reaction of DIP*+ takes place mainly in the absence of active HRP and in this phase the combination of, at least, two second-order kinetic processes is needed to model the experimental data. Our data suggest that HRP oxidizes DIP in general by a two-electron process or that the cation radical is very unstable so that the one-electron process is only detected in the presence of anionic surfactant, which stabilizes significantly the DIP*+ intermediate.
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Affiliation(s)
- Luis Eduardo Almeida
- Instituto de Química de São Carlos, Universidade de São Paulo, C.P.780, 13560-970 São Carlos, SP, Brasil
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Ling KQ, Sayre LM. Horseradish peroxidase-mediated aerobic and anaerobic oxidations of 3-alkylindoles. Bioorg Med Chem 2005; 13:3543-51. [PMID: 15848767 DOI: 10.1016/j.bmc.2005.02.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2004] [Revised: 02/05/2005] [Accepted: 02/09/2005] [Indexed: 11/29/2022]
Abstract
Little is known about the HRP-mediated oxidations of 3-alkylindoles. Whereas 3-methylindole and 3-ethylindole were found to be turned over smoothly by HRP, reactions of tryptophol and N-acetyltryptamine were inefficient. Oxidations of the former two indoles by HRP under aerobic conditions led to the corresponding ring-opened o-acylformanilides and oxindoles, whereas anaerobic oxidations resulted in oxidative dimerization. The major products of anaerobic oxidation of 3-methylindole were shown to be two hydrated dimers, while anhydrodimers were obtained in the 3-ethyl case. The proposed mechanism involves HRP-mediated one-electron oxidation to give an indole radical that either dimerizes (anaerobic conditions) or reacts with O2 (aerobic conditions). Measured kinetics of indole oxidation by HRP compounds I and II mirrored their relative reactivities under turnover conditions. The observed comparable binding affinities for all four indole substrates investigated suggest that the low reactivity of tryptophol and N-acetyltryptamine reflect binding to HRP in an orientation that is disadvantageous to electron transfer oxidation of the indole ring.
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Affiliation(s)
- Ke-Qing Ling
- Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, USA
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Metzler DE, Metzler CM, Sauke DJ. Transition Metals in Catalysis and Electron Transport. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50019-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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8
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Reszka KJ, Matuszak Z, Chignell CF, Dillon J. Oxidation of biological electron donors and antioxidants by a reactive lactoperoxidase metabolite from nitrite (NO2-): an EPR and spin trapping study. Free Radic Biol Med 1999; 26:669-78. [PMID: 10218656 DOI: 10.1016/s0891-5849(98)00244-5] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We report that a lactoperoxidase (LPO) metabolite derived from nitrite (NO2-) catalyses one-electron oxidation of biological electron donors and antioxidants such as NADH, NADPH, cysteine, glutathione, ascorbate, and Trolox C. The radical products of the reaction have been detected and identified using either direct EPR or EPR combined with spin trapping. While LPO/H2O2 alone generated only minute amounts of radicals from these compounds, the yield of radicals increased sharply when nitrite was also present. In aerated buffer (pH 7) the nitrite-dependent oxidation of NAD(P)H by LPO/H2O2 produced superoxide radical, O2*-, which was detected as a DMPO/*O2H adduct. We propose that in the LPO/H2O2/NO2-/biological electron donor systems the nitrite functions as a catalyst because of its preferential oxidation by LPO to a strongly oxidizing metabolite, most likely a nitrogen dioxide radical *NO2, which then reacts with the biological substrates more efficiently than does LPO/H2O2 alone. Because both nitrite and peroxidase enzymes are ubiquitous our observations point at a possible mechanism through which nitrite might exert its biological and cytotoxic action in vivo, and identify some of the physiological targets which might be affected by the peroxidase/H2O2/nitrite systems.
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Affiliation(s)
- K J Reszka
- Department of Ophthalmology, Columbia University, New York, NY, USA.
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Abstract
The kinetics of luminol oxidation catalyzed by horseradish peroxidase (HRP), Arthromyces ramosus peroxidase (ARP) and lactoperoxidase (LPO) at pH 7.0 was investigated. One-electron oxidation of luminol by peroxidase systems was inferred from the detection of luminol radicals, luminol-mediated formation of ascorbate radicals, and the trapping of luminol-mediated GSH radicals. The catalytic intermediate of peroxidases in the steady state was Compound II and the rate constants of HRP, ARP, and LPO Compound II with luminol were 3.6 x 10(4), 1.1 x 10(7), and 2.5 x 10(4) M(-1)s(-1), respectively. The intensity of luminol chemiluminescence (CL) generated by the peroxidases depended on the rate constants of the rate-determining step. The luminol CL catalyzed by peroxidases increased with an increase in the concentration of H2O2 and was inhibited in the presence of catalase. Neither oxygen consumption during the reaction under aerobic conditions nor a change of light intensity under anaerobic conditions was observed. The light emission and oxidation of luminol catalyzed by LPO was increased by trace amounts of iodide. LPO catalyzes two-electron oxidations of iodide to form iodinating intermediate (Nakamura, M.; et al. J. Biol. Chem. 260:13546-13552, 1985), which subsequently oxidizes luminol. The results lead us to conclude that CL of luminol was initiated by peroxidase systems irrespective of one- or two-electron oxidations of luminol.
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Affiliation(s)
- M Nakamura
- Department of Chemistry, Asahikawa Medical College, Japan
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Mitani M, Yokoyama Y, Ichikawa S, Sawada H, Matsumoto T, Fujimori K, Kosugi M. Determination of horseradish peroxidase concentration using the chemiluminescence of Cypridina luciferin analogue, 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-one. JOURNAL OF BIOLUMINESCENCE AND CHEMILUMINESCENCE 1994; 9:355-61. [PMID: 7879651 DOI: 10.1002/bio.1170090602] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The chemiluminescence of the Cypridina luciferin analogue, 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin++ +-3-one (MCLA) was observed at 462 nm in the presence of horseradish peroxidase (HRP) and the total spectrum of light emitted was found to depend linearly on HRP concentration. Methods for the determination of HRP concentration using the chemiluminescence was investigated. HRP could be detected in the range from 100 pmol/L to 100 nmol/L under the optimum condition, H2O2 (10 mmol/L) and MCLA (10 mumol/L) at pH 5.8.
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Affiliation(s)
- M Mitani
- Tsukuba Research Laboratory, NOF Corporation, Ibaraki, Japan
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Kamidate T, Katayama A, Ichihashi H, Watanabe H. Characterization of peroxidases in luminol chemiluminescence coupled with copper-catalysed oxidation of cysteamine. JOURNAL OF BIOLUMINESCENCE AND CHEMILUMINESCENCE 1994; 9:279-86. [PMID: 7985529 DOI: 10.1002/bio.1170090406] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Hydrogen peroxide formed during the course of the copper(II)-catalysed oxidation of cysteamine with oxygen was continuously determined by a peroxidase (POD)-catalysed luminol chemiluminescence (CL) method. Horseradish peroxidase (HRP), lactoperoxidase (LPO) and Arthromyces ramosus peroxidase (ARP) were used as a CL catalyst. The respective PODs gave specific CL intensity-time profiles. HRP caused a CL delay, and ARP gave a time-response curve which followed the production rate of H2O2. LPO gave only a weak CL flash which decayed promptly. These differences of CL response curves could be explained in terms of the different reactivities of PODs for superoxide anion and the different formation rate of luminol radicals in the peroxidation of luminol catalysed by POD.
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Affiliation(s)
- T Kamidate
- Faculty of Engineering, Hokkaido University, Sapporo, Japan
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de Melo MP, Cilento G. Chemiexcitation in the peroxidative metabolism of N-methylcarbazole: mechanistic implications. Photochem Photobiol 1994; 59:677-82. [PMID: 8066126 DOI: 10.1111/j.1751-1097.1994.tb09675.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The peroxidative metabolism of N-methylcarbazole emits light independently of the presence of oxygen. It is likely that two chemiexcited transients are formed by electron transfer to the activated peroxidase, the cation radical by one electron transfer and a cation biradical by two electron transfer consistent with the failure to observe horseradish peroxidase-II in the steady state of the reaction. In the spectral range investigated (390-700 nm) the observed emission (570-700 nm) is ascribed to the biradical, as the latter is equivalent to an excited state of the postulated iminium cation. While lipoxygenase has no effect upon N-methylcarbazole, it markedly enhances the emission if peroxidase is present. This effect requires oxygen and is ascribed to an excited product formed by lipoxygenase acting upon an intermediate hydroperoxide of the aerobic process promoted by peroxidase. Our results are of importance on two counts. First they extend to N-methylcarbazole the formation of excited species in the peroxidative metabolism of important xenobiotics. Second, the mechanistic information they provide supports the scheme of metabolism postulated by Kedderis et al. (1986, J. Biol. Chem. 261, 15910-15914).
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Affiliation(s)
- M P de Melo
- Department of Biochemistry, Universidade de São Paulo, Brazil
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Melo MPDE, Cilento G. CHEMIEXCITATION IN THE PEROXIDATIVE METABOLISM OF N- METHYLCARBAZOLE: MECHANISTIC IMPLICATIONS. Photochem Photobiol 1994. [DOI: 10.1111/j.1751-1097.1994.tb08237.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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14
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Hosoya T, Yoshimura H, Naito N, Suzuki N, Sato K, Takamatsu J. Isolation of thyroid peroxidase from patients with Graves' disease and comparison with animal peroxidases. THE INTERNATIONAL JOURNAL OF BIOCHEMISTRY 1994; 26:351-65. [PMID: 8187932 DOI: 10.1016/0020-711x(94)90055-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
1. Human thyroid peroxidase (TPO) was isolated from 280-640 g of pooled thyroid tissue resected from patients with Graves' disease. 2. Isolation was performed by an improved and simplified method. 3. The Reinheit Zahl (A412/A280) of the final preparations was in the range of 0.16-0.32. 4. The spectroscopic and enzymatic properties of Graves' TPO were compared with those of porcine TPO and bovine LPO, revealing closer resemblance to the former. 5. Graves' TPO may provide a useful substitute for normal TPO, which is very difficult to isolate.
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Affiliation(s)
- T Hosoya
- Faculty of Pharmaceutical Sciences, Chiba University, Japan
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Chang CS, Sinclair R, Khalid S, Yamazaki I, Nakamura S, Powers L. An extended X-ray absorption fine structure investigation of the structure of the active site of lactoperoxidase. Biochemistry 1993; 32:2780-6. [PMID: 8457545 DOI: 10.1021/bi00062a007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Native lactoperoxidase, compound III, and the reduced forms (at pH 6 and 9) were studied using X-ray absorption spectroscopy (XAS). Native lactoperoxidase has four pyrrole nitrogen ligands at an average distance of 2.04 +/- 0.01 A, a proximal ligand at 1.91 +/- 0.02 A, and a sixth (distal) ligand at 2.16 +/- 0.03 A. Lactoperoxidase native enzyme has a first coordination shell structure that is similar to that of native lignin peroxidase [Sinclair, R., Yamazaki, I., Bumpus, J., Brock, B., Chang, C.-S., Albo, A., & Powers, L. (1992) Biochemistry 31, 4892-4900] and different from that of horseradish peroxidase [Chance, B., Powers, L., Ching, Y., Poulos, T., Schonbaum, G., Yamazaki, I., & Paul, K. (1984) Arch. Biochem. Biophys. 235, 596-611]. Similarly, lactoperoxidase compound III resembles lignin peroxidase compound III. The five-coordinated ferrous form was stable at pH 9, but at pH 6 it was rapidly converted to the six-coordinated form with a distal ligand at 2.18 +/- 0.03 A. No evidence typical of changes in spin state was obtained at the different pH values.
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Affiliation(s)
- C S Chang
- National Center for the Design of Molecular Function, Utah State University, Logan 84322-4630
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Nakamura M, Hayashi T. Oxidation mechanism of vitamin E analogue (Trolox C, 6-hydroxy-2,2,5,7,8-pentamethylchroman) and vitamin E by horseradish peroxidase and myoglobin. Arch Biochem Biophys 1992; 299:313-9. [PMID: 1332620 DOI: 10.1016/0003-9861(92)90280-a] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The oxidation of 6-hydroxy-2,2,5,7,8-pentamethylchroman, Trolox C, and alpha-tocopherol by horseradish peroxidase was examined by stopped-flow and ESR experiments. The catalytic intermediate of horseradish peroxidase during the oxidation of vitamin E analogues and vitamin E was invariably Compound II, and rate constants for the rate-determining step decreased in the order 6-hydroxy-2,2,5,7,8-pentamethylchroman > Trolox C > alpha-tocopherol. The formation of phenoxyl radicals from substrates was verified with ESR and was followed optically. Resulting 6-hydroxy-2,2,5,7,8-pentamethylchroman and Trolox C radicals decayed through a dismutation reaction, followed by formation of the quinoid form via a transient intermediate. The sequence of events after formation of 6-hydroxy-2,2,5,7,8-pentamethylchroman and Trolox C radicals was similar to that observed by pulse radiolysis (Thomas, M. J., and Bielski, B. H. J. (1989). J. Am. Chem. Soc. 111, 3315-3319). Final oxidation products of 6-hydroxy-2,2,5,7,8-pentamethylchroman and Trolox C were identified as the quinoid forms and were obtained quantitatively whether or not the analogue had a carboxyl or methyl group at the 2-position of chroman ring. In contrast, enzymatic oxidation of alpha-tocopherol gave alpha-tocopherol quinone in very low yield. Conversion of 6-hydroxy-2,2,5,7,8-pentamethylchroman, Trolox C, and alpha-tocopherol to the corresponding quinones was also catalyzed by metmyoglobin in a reaction completely inhibited by ascorbate.
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Affiliation(s)
- M Nakamura
- Research Institute for Electronic Science, Hokkaido University, Sapporo, Japan
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Abstract
In routine guaiacol assays for thyroid peroxidase and lactoperoxidase employing a newly purchased bottle of guaiacol from Aldrich Chemical Co., we were surprised to find the formation of a blue color instead of the expected amber color classically associated with this assay. This was observed also with horseradish, myelo-, and cytochrome c peroxidase. The blue color (Amax approximately 650 nm) was not formed with guaiacol reagents obtained from two other chemical companies, nor was it seen with a bottle of old Aldrich guaiacol that had been in use in the laboratory for more than 10 years. In the present investigation we provide evidence that formation of the blue color is closely associated with the presence of a low concentration of catechol (approximately 0.5 mol%) in the new Aldrich guaiacol reagent. Catechol itself, even in much higher concentration, is a very weak donor for peroxidase, forming a light pink color. The blue color in Aldrich new guaiacol is not formed to the exclusion of 470-nm-absorbing product(s). Formation of the latter is, however, inhibited, and use of Aldrich new guaiacol for assay leads to low values for peroxidase activity. Other dihydroxyphenols (resorcinol and hydroquinone) do not mimic the action of catechol in formation of the blue color. Resorcinol is a very potent inhibitor of peroxidation of guaiacol. Possible schemes are proposed for formation of the products that may be associated with the amber and blue colors.
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Affiliation(s)
- A Taurog
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235
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Bhattacharyya D, Bandyopadhyay U, Banerjee R. Chemical and kinetic evidence for an essential histidine in horseradish peroxidase for iodide oxidation. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)50164-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Kettle A, Winterbourn C. Oxidation of hydroquinone by myeloperoxidase. Mechanism of stimulation by benzoquinone. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42445-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Kettle AJ, Winterbourn CC. Mechanism of inhibition of myeloperoxidase by anti-inflammatory drugs. Biochem Pharmacol 1991; 41:1485-92. [PMID: 1850278 DOI: 10.1016/0006-2952(91)90565-m] [Citation(s) in RCA: 137] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Hypochlorous acid (HOCl) is the most powerful oxidant produced by human neutrophils, and should therefore be expected to contribute to the damage caused by these inflammatory cells. It is produced from H2O2 and Cl- by the heme enzyme myeloperoxidase (MPO). We used a H2O2-electrode to assess the ability of a variety of anti-inflammatory drugs to inhibit conversion of H2O2 to HOCl. Dapsone, mefenamic acid, sulfapyridine, quinacrine, primaquine and aminopyrine were potent inhibitors, giving 50% inhibition of the initial rate of H2O2 loss at concentrations of about 1 microM or less. Phenylbutazone, piroxicam, salicylate, olsalazine and sulfasalazine were also effective inhibitors. Spectral investigations showed that the inhibitors acted by promoting the formation of compound II, which is an inactive redox intermediate of MPO. Ascorbate reversed inhibition by reducing compound II back to the active enzyme. The characteristic properties that allowed the drugs to inhibit MPO reversibly were ascertained by determining the inhibitory capacity of related phenols and anilines. Inhibition increased as substituents on the aromatic ring became more electron withdrawing, until an optimum reduction potential was reached. Beyond this optimum, their inhibitory capacity declined. The best inhibitor was 4-bromoaniline which had an I50 of 45 nM. An optimum reduction potential enables inhibitors to reduce MPO to compound II, but prevents them from reducing compound II back to the active enzyme. Exploitation of this optimum reduction potential will help in targeting drugs against HOCl-dependent tissue damage.
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Affiliation(s)
- A J Kettle
- Department of Pathology, Christchurch School of Medicine, New Zealand
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21
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Kinetic and molecular orbital studies on the rate of oxidation of monosubstituted phenols and anilines by lactoperoxidase compound II in comparison with the case of horseradish peroxidase. J Biol Phys 1991. [DOI: 10.1007/bf00417806] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
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22
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Libby R, Rotberg N. Compound I formation is a partially rate-limiting process in chloroperoxidase-catalyzed bromination reactions. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(18)77185-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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23
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Verma S, Kumar GP, Laloraya M, Singh A. Activation of iodine into a free-radical intermediate by superoxide: a physiologically significant step in the iodination of tyrosine. Biochem Biophys Res Commun 1990; 170:1026-34. [PMID: 2167666 DOI: 10.1016/0006-291x(90)90495-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A pivotal biochemical event in the thyroid physiology is identified unravelling a superoxide anion radical-mediated activation of iodine into an active I.- form, which could be the intermediate that is incorporated onto tyrosine. This active iodine species gives fairly stable spin-adducts with PBN that could be characterized using EPR spectroscopy. Thus, a long-lasting puzzle regarding the iodine intermediate formed before iodination of tyrosine seems to be solved.
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Affiliation(s)
- S Verma
- School of Life Sciences, Devi Ahilya Vishwavidyalaya, Indore, India
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24
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Fukuzawa A, Aye M, Nakamura M, Tamura M, Murai A. Biosynthetic Formation of Cyclic Bromo-ethers Initiated by Lactoperoxidase. CHEM LETT 1990. [DOI: 10.1246/cl.1990.1287] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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25
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Pérez U, Dunford HB. Spectral studies on the oxidation of organic sulfides (thioanisoles) by horseradish peroxidase compounds I and II. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1038:98-104. [PMID: 2317520 DOI: 10.1016/0167-4838(90)90016-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Using both rapid-scan and conventional spectrophotometry, oxygenation of p-substituted thioanisoles by horseradish peroxidase compounds I and II was investigated at pH 5, 7 and 9. The pH-jump technique was applied to the compound II reactions at acidic and neutral pH. The rate of oxidation of the sulfides is dependent on pH, concentration of substrate and on the different substituents in the para position of the benzene ring. Our results, based on transient state observations of the enzyme intermediates, are in agreement with the results of Kobayashi, S., Minoru, N., Kimura, T. and Schaap, A.P. (Biochemistry (1987) 26, 5019-5022), obtained using 18O-labelling and studies of product formation, in which formation of a sulfur cation radical from compound I is proposed. We consider two reaction mechanisms for the compound II reaction: one a one-electron oxidation of the thioanisole, analogous to the compound I reaction, and the other, the attack of the hydroxyl radical originating from compound II on the sulfur-cation radical.
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Affiliation(s)
- U Pérez
- Department of Chemistry, University of Alberta, Edmonton, Canada
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26
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Kobayashi K, Hayashi K, Swallow AJ. Reactions of the NAD radical with higher oxidation states of horseradish peroxidase. Biochemistry 1990; 29:2080-4. [PMID: 2328239 DOI: 10.1021/bi00460a017] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The reactions of the NAD radical (NAD.) with ferric horseradish peroxidase and with compounds I and II were investigated by pulse radiolysis. NAD. reacted with the ferric enzyme and with compound I to form the ferrous enzyme and compound II with second-order rate constants of 8 X 10(8) and 1.5 X 10(8) M-1 s-1, respectively, at pH 7.0. In contrast, no reaction of NAD. with native compound II at pH 10.0 nor with diacetyldeutero-compound II at pH 5.0-8.0 could be detected. Other reducing species generated by pulse radiolysis, such as hydrated electron (eaq-), superoxide anion (O2-), and benzoate anion radical, could not reduce compound II of the enzyme to the ferric state, although the methylviologen radical reduced it. The results are discussed in relation to the mechanism of catalysis of the one-electron oxidation of substrates by peroxidase.
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Affiliation(s)
- K Kobayashi
- Institute of Scientific and Industrial Research, Osaka University, Japan
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27
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Abstract
Studies with biomimetic models can yield considerable insight into mechanisms of enzymatic catalysis. The discussion above indicates how such information has been important in the cases of flavoproteins, hemoproteins, and, to a lesser extent, the copper protein dopamine beta-hydroxylase. Some of the moieties that we generally accept as intermediates (i.e., high-valent iron oxygen complex in cytochrome P-450 reactions) would be extremely hard to characterize were it not for biomimetic models and more stable analogs such as peroxidase Compound I complexes. Although biomimetic models can be useful, we do need to keep them in perspective. It is possible to alter ligands and aspects of the environment in a way that may not reflect the active site of the protein. Eventually, the model work needs to be carried back to the proteins. We have seen that diagnostic substrates can be of considerable use in understanding enzymes and examples of elucidation of mechanisms through the use of rearrangements, mechanism-based inactivation, isotope labeling, kinetic isotope effects, and free energy relationships have been given. The point should be made that a myriad of approaches need to be applied to the study of each enzyme, for there is potential for misleading information if total reliance is placed on a single approach. The point also needs to be made that in the future we need information concerning the structures of the active sites of enzymes in order to fully understand them. Of the enzymes considered here, only a bacterial form of cytochrome P-450 (P-450cam) has been crystallized. The challenge to determine the three-dimensional structures of these enzymes, particularly the intrinsic membrane proteins, is formidable, yet our further understanding of the mechanisms of enzyme catalysis will remain elusive as long as we have to speak of putative specific residues, domains, and distances in anecdotal terms. The point should be made that there is actually some commonality among many of the catalytic mechanisms of oxidation, even among proteins with different structures and prosthetic groups. Thus, we see that cytochrome P-450 has some elements of a peroxidase and vice versa; indeed, the chemistry at the prosthetic group is probably very similar and the overall chemistry seems to be induced by the protein structure. The copper protein dopamine beta-hydroxylase appears to proceed with chemistry similar to that of the hemoprotein cytochrome P-450 and, although not so thoroughly studied, the non-heme iron protein P. oleovarans omega-hydroxylase.(ABSTRACT TRUNCATED AT 400 WORDS)
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28
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Resonance Raman characterization of heme Fe(IV)=O groups of intermediates of yeast cytochrome C peroxidase and lactoperoxidase. J Mol Struct 1989. [DOI: 10.1016/0022-2860(89)80004-3] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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29
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Millis CD, Cai DY, Stankovich MT, Tien M. Oxidation-reduction potentials and ionization states of extracellular peroxidases from the lignin-degrading fungus Phanerochaete chrysosporium. Biochemistry 1989; 28:8484-9. [PMID: 2605198 DOI: 10.1021/bi00447a032] [Citation(s) in RCA: 83] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The oxidation-reduction potentials of lignin peroxidase isozymes H1, H2, H8, and H10 as well as the Mn-dependent peroxidase isozymes H3 and H4 are reported. The potentiometric titrations involving the ferrous and ferric states of the enzyme had Nernst plots indicating single-electron transfer. The Em7 values of lignin peroxidase isozymes H1, H2, H8, and H10 are -142, -135, -137, and -127 mV versus standard hydrogen electrode, respectively. The Em7 values for the Mn-dependent peroxidase isozymes H3 and H4 are -88 and -93 mV versus standard hydrogen electrode, respectively. The midpoint potential of H1, H8, and H4 remained unchanged in the presence of their respective substrates, veratryl alcohol and Mn(II). The midpoint potential between the ferric and ferrous forms of isozymes H1 and H4 exhibited a pH-dependent change between pH 3.5 and pH 6.5. These results indicate that the reductive half-reaction of the enzymes is the following: ferric peroxidase + le- + H+----ferrous peroxidase. Above pH 6.5, the effect of pH on the midpoint potential is diminished and indicates that an ionization with an apparent pKa equal to approximately 6.6-6.7 occurs in the reduced form of the enzymes. A heme-linked ionization group in the ferrous form of the enzymes was confirmed by studying the effect of pH on the absorption spectra of isozymes H1 and H4. These spectrophotometric pH titration experiments confirmed the electrochemical results indicating pKa values of 6.59 and 6.69 for reduced isozymes H1 and H4, respectively. These results indicate the presence of a heme-linked ionization of an amino acid in the reduced form of the lignin peroxidase isozymes similar to that of other plant peroxidases.
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Affiliation(s)
- C D Millis
- Department of Molecular and Cell Biology, Pennsylvania State University, University Park 16802
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30
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The chloride-activated peroxidation of catechol as a mechanistic probe of chloroperoxidase reactions. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)84823-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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31
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Holler TP, Hopkins PB. A qualitative fluorescence-based assay for tyrosyl radical scavenging activity: ovothiol A is an efficient scavenger. Anal Biochem 1989; 180:326-30. [PMID: 2817362 DOI: 10.1016/0003-2697(89)90440-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
A method for determining relative tyrosyl radical scavenging activity of antioxidants which requires only a standard fluorometer and commercially available materials is presented. Ultraviolet irradiation of aqueous tyrosine solutions containing superoxide dismutase and catalase produces fluorescent dityrosine residues via dimerization of photogenerated tyrosyl radicals. Added antioxidants suppress the buildup of fluorescence by scavenging the tyrosyl radicals. A correlation exists between the ability of a substance to suppress dityrosine formation and the substance's one-electron oxidation potential. This method demonstrates that ovothiol A scavenges tyrosyl radicals much more efficiently than glutathione or cysteine, resembling instead the known biological radical scavengers uric acid and ascorbic acid and the alpha-tocopherol analog trolox.
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Affiliation(s)
- T P Holler
- Department of Chemistry, University of Washington, Seattle 98195
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32
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Silva E, Cilento G. DUAL EFFECTS OF TRYPTOPHAN IN THE HORSERADISH PEROXIDASE SYSTEM THAT GENERATES TRIPLET ACETONE. Photochem Photobiol 1989. [DOI: 10.1111/j.1751-1097.1989.tb04157.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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33
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Nakamura M, Yamazaki I, Kotani T, Ohtaki S. Thyroglobulin-mediated One- and Two-electron Oxidations of Glutathione and Ascorbate in Thyroid Peroxidase Systems. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)51574-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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34
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Svensson BE. Involvement of cysteine, serotonin and their analogues in peroxidase-oxidase reactions. Chem Biol Interact 1989; 70:305-21. [PMID: 2545363 DOI: 10.1016/0009-2797(89)90052-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Myeloperoxidase-oxidase reactions with close to physiological concentrations of thiols and phenols were studied. Cysteine was shown to be a myeloperoxidase-oxidase substrate when catalytic amounts of serotonin were added as cosubstrate. Penicillamine could be substituted for cysteine and acetaminophen could be substituted for serotonin. The properties of these peroxidase-oxidase reactions, e.g. the dependence on substrate and myeloperoxidase concentration, reduced oxygen species, metal ions and pH, were studied. Also, eosinophil, lacto- and horseradish peroxidase could catalyse these reactions.
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Affiliation(s)
- B E Svensson
- Research and Development Department, Södertälje, Sweden
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35
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Kohler H, Taurog A, Dunford HB. Spectral studies with lactoperoxidase and thyroid peroxidase: interconversions between native enzyme, compound II, and compound III. Arch Biochem Biophys 1988; 264:438-49. [PMID: 3401009 DOI: 10.1016/0003-9861(88)90309-8] [Citation(s) in RCA: 63] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Spectral scans in both the visible (650-450 nm) and the Soret (450-380 nm) regions were recorded for the native enzyme, Compound II, and Compound III of lactoperoxidase and thyroid peroxidase. Compound II for each enzyme (1.7 microM) was prepared by adding a slight excess of H2O2 (6 microM), whereas Compound III was prepared by adding a large excess of H2O2 (200 microM). After these compounds had been formed it was observed that they were slowly reconverted to the native enzyme in the absence of exogenous donors. The pathway of Compound III back to the native enzyme involved Compound II as an intermediate. Reconversion of Compound III to native enzyme was accompanied by the disappearance of H2O2 and generation of O2, with approximately 1 mol of O2 formed for each 2 mol of H2O2 that disappeared. A scheme is proposed to explain these observations, involving intermediate formation of the ferrous enzyme. According to the scheme, Compound III participates in a reaction cycle that effectively converts H2O2 to O2. Iodide markedly affected the interconversions between native enzyme, Compound II, and Compound III for lactoperoxidase and thyroid peroxidase. A low concentration of iodide (4 microM) completely blocked the formation of Compound II when lactoperoxidase or thyroid peroxidase was treated with 6 microM H2O2. When the enzymes were treated with 200 microM H2O2, the same low concentration of iodide completely blocked the formation of Compound III and largely prevented the enzyme degradation that otherwise occurred in the absence of iodide. These effects of iodide are readily explained by (i) the two-electron oxidation of iodide to hypoiodite by Compound I, which bypasses Compound II as an intermediate, and (ii) the rapid oxidation of H2O2 to O2 by the hypoiodite formed in the reaction between Compound I and iodide.
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Affiliation(s)
- H Kohler
- Department of Pharmacology, University of Texas Health Science Center, Dallas 75235
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36
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37
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Frydman RB, Rosenfeld J, Camoretti-Mercado B, Peisach J. Porphobilinogen oxygenase. Purification and evidence of its hemoprotein structure. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(18)48146-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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38
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Kobayashi S, Nakano M, Kimura T, Schaap AP. On the mechanism of the peroxidase-catalyzed oxygen-transfer reaction. Biochemistry 1987; 26:5019-22. [PMID: 3663642 DOI: 10.1021/bi00390a020] [Citation(s) in RCA: 108] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
We reported evidence that horseradish peroxidase (HRP) and chloroperoxidase (CPO) catalyze oxygen transfer from H2O2 to thioanisoles [Kobayashi, S., Nakano, M., Goto, T., Kimura, T., & Schaap, A. P. (1986) Biochem. Biophys. Res. Commun. 135, 166-171]. In the present paper, the reaction mechanism of this oxygen transfer is discussed. The oxidation of para-substituted thioanisoles by HRP compound II showed a large negative rho value of -1.46 vs. the sigma + parameter in a Hammett plot. These results are in accord with the formation of a cation radical intermediate in the rate-determining step. Hammett treatments for HRP- and CPO-dependent S-oxygenations did not provide unequivocal proofs to judge the reaction mechanism, because of the poor correlations for sigma + and sigma p parameters. Different behavior was found in kinetics and stereoselectivity between the two enzymes. Results in the present study and recent studies strongly suggested the formation of a cation radical intermediate. The oxygen atom would transfer by reaction of compound II and the cation radical intermediate. Although involvement of the cation radical was not confirmed in the CPO system, a similar mechanism was proposed for CPO.
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Affiliation(s)
- S Kobayashi
- Department of Chemistry, Wayne State University, Detroit, Michigan 48202
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39
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40
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Meunier B. Horseradish peroxidase: a useful tool for modeling the extra-hepatic biooxidation of exogens. Biochimie 1987; 69:3-9. [PMID: 3101748 DOI: 10.1016/0300-9084(87)90266-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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41
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Abstract
Free radicals are formed in prosthetic groups or amino acid residues of certain enzymes. These free radicals are closely related to the activation process in enzyme catalysis, but their formation does not always result in the formation of substrate free radicals as a product of the enzyme reaction. The role of free radicals in enzyme catalysis is discussed.
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Affiliation(s)
- I Yamazaki
- Biophysics Division, Hokkaido University, Sapporo, Japan
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42
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Taketa K, Ichikawa E, Hanada T. A tetrazolium method for staining peroxidase labels in blotting assays. J Immunol Methods 1986; 95:71-7. [PMID: 2431066 DOI: 10.1016/0022-1759(86)90319-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A sensitive staining method of horseradish peroxidase-labeled immunoglobulins on nitrocellulose membrane was established by employing a reaction chain leading to formazan formation with phenol as a substrate of peroxidase and NADH as a hydrogen donor to reduce nitro blue tetrazolium. Higher concentrations of NADH relative to phenol were necessary to increase the intensity of staining and to ensure a wide dose-response range of color production with respect to the applied enzyme activities. By an optimized tetrazolium method in combination with antibody-affinity blotting, as low as 4 ng/ml alpha-fetoprotein was detected and 3-4-fold greater color intensities in a working assay range as compared with those of existing methods were obtained. The present technique of peroxidase staining may prove to have a wide application for the enzyme immunoassay using blotting modalities.
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43
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Characterization of one- and two-electron oxidations of glutathione coupled with lactoperoxidase and thyroid peroxidase reactions. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(18)66960-1] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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