Characterization of the Oxidase Activity in Mammalian Catalase

Abstract

Catalase is a highly conserved heme-containing antioxidant enzyme known for its ability to degrade hydrogen peroxide into water and oxygen. In low concentrations of hydrogen peroxide, the enzyme also exhibits peroxidase activity. We report that mammalian catalase also possesses oxidase activity. This activity, which is detected in purified catalases, cell lysates, and intact cells, requires oxygen and utilizes electron donor substrates in the absence of hydrogen peroxide or any added cofactors. Using purified bovine catalase and 10-acetyl-3,7-dihydroxyphenoxazine as the substrate, the oxidase activity was found to be temperature-dependent and displays a pH optimum of 7–9. The Km for the substrate is 2.4 × 10-4 m, and Vmax is 4.7 × 10-5 m/s. Endogenous substrates, including the tryptophan precursor indole, the neurotransmitter precursor β-phenylethylamine, and a variety of peroxidase and laccase substrates, as well as carcinogenic benzidines, were found to be oxidized by catalase or to inhibit this activity. Several dietary plant micronutrients that inhibit carcinogenesis, including indole-3-carbinol, indole-3-carboxaldehyde, ferulic acid, vanillic acid, and epigallocatechin-3-gallate, were effective inhibitors of the activity of catalase oxidase. Difference spectroscopy revealed that catalase oxidase/substrate interactions involve the heme-iron; the resulting spectra show time-dependent decreases in the ferric heme of the enzyme with corresponding increases in the formation of an oxyferryl intermediate, potentially reflecting a compound II-like intermediate. These data suggest a mechanism of oxidase activity involving the formation of an oxygen-bound, substrate-facilitated reductive intermediate. Our results describe a novel function for catalase potentially important in metabolism of endogenous substrates and in the action of carcinogens and chemopreventative agents. Catalase is a highly conserved heme-containing antioxidant enzyme known for its ability to degrade hydrogen peroxide into water and oxygen. In low concentrations of hydrogen peroxide, the enzyme also exhibits peroxidase activity. We report that mammalian catalase also possesses oxidase activity. This activity, which is detected in purified catalases, cell lysates, and intact cells, requires oxygen and utilizes electron donor substrates in the absence of hydrogen peroxide or any added cofactors. Using purified bovine catalase and 10-acetyl-3,7-dihydroxyphenoxazine as the substrate, the oxidase activity was found to be temperature-dependent and displays a pH optimum of 7–9. The Km for the substrate is 2.4 × 10-4 m, and Vmax is 4.7 × 10-5 m/s. Endogenous substrates, including the tryptophan precursor indole, the neurotransmitter precursor β-phenylethylamine, and a variety of peroxidase and laccase substrates, as well as carcinogenic benzidines, were found to be oxidized by catalase or to inhibit this activity. Several dietary plant micronutrients that inhibit carcinogenesis, including indole-3-carbinol, indole-3-carboxaldehyde, ferulic acid, vanillic acid, and epigallocatechin-3-gallate, were effective inhibitors of the activity of catalase oxidase. Difference spectroscopy revealed that catalase oxidase/substrate interactions involve the heme-iron; the resulting spectra show time-dependent decreases in the ferric heme of the enzyme with corresponding increases in the formation of an oxyferryl intermediate, potentially reflecting a compound II-like intermediate. These data suggest a mechanism of oxidase activity involving the formation of an oxygen-bound, substrate-facilitated reductive intermediate. Our results describe a novel function for catalase potentially important in metabolism of endogenous substrates and in the action of carcinogens and chemopreventative agents. Mammalian catalase belongs to a family of Fe-protoporphyrin IX containing proteins that include a variety of cytochromes, globins, and peroxidases and is one of the best characterized antioxidant enzymes (1Deisseroth A. Dounce A.L. Physiol. Rev. 1970; 50: 319-375Crossref PubMed Scopus (530) Google Scholar). As a homotetrameric heme-containing enzyme, it is known for its ability to convert hydrogen peroxide into water and oxygen (catalatic activity), and in the presence of low concentrations of hydrogen peroxide to oxidize low molecular weight alcohols (peroxidatic activity). The conversion of hydrogen peroxide to water and oxygen by catalase is a two-step process whereby catalase heme Fe3+ reduces one molecule of hydrogen peroxide to water, generating a covalent Fe4+=O oxyferryl species and a porphyrin cation radical. This reaction intermediate, referred to as compound I, then oxidizes a second hydrogen peroxide molecule forming molecular oxygen and water (1Deisseroth A. Dounce A.L. Physiol. Rev. 1970; 50: 319-375Crossref PubMed Scopus (530) Google Scholar, 2Ivancich A. Jouve H.M. Sartor B. Gaillard J. Biochemistry. 1997; 36: 9356-9364Crossref PubMed Scopus (131) Google Scholar, 3Jones P. Dunford H.B. J. Theor. Biol. 1977; 69: 457-470Crossref PubMed Scopus (67) Google Scholar) (see Fig. 1). The peroxidatic activity of catalase results from the ability of compound I to oxidize alcohols to aldehydes and water (4Keilin D. Hartree E.F. Biochem. J. 1951; 49: 88-104Crossref PubMed Google Scholar, 5Keilin D. Hartree E.F. Biochem. J. 1955; 60: 310-325Crossref PubMed Scopus (83) Google Scholar, 6Kremer M.L. Biochim. Biophys. Acta. 1970; 198: 199-209Crossref PubMed Scopus (47) Google Scholar) (Fig. 1). Each catalase monomer binds one molecule of heme; the holoenzyme also binds two molecules of NADPH, although the precise role of this cofactor in enzymatic activity is unclear, because hydrogen peroxide provides both oxidative and reductive potential during catalysis. Recent studies suggest that NADPH may be important in maintaining catalase in an active state (7Kirkman H.N. Rolfo M. Ferraris A.M. Gaetani G.F. J. Biol. Chem. 1999; 274: 13908-13914Abstract Full Text Full Text PDF PubMed Scopus (215) Google Scholar). In mammalian cells, catalase is found at high concentrations in peroxisomes, along with a variety of oxidases and peroxidases (8Chance B. Oshino N. Biochem. J. 1971; 122: 225-233Crossref PubMed Scopus (84) Google Scholar). It has been suggested that the enzyme protects cells by removing hydrogen peroxide produced by flavin containing oxidases in the peroxisome, thereby preventing the accumulation of toxic levels of this reactive oxygen intermediate (9Kehrer J.P. Crit. Rev. Toxicol. 1993; 23: 21-48Crossref PubMed Scopus (1326) Google Scholar). However, hydrogen peroxide is important for an array of activities, including peroxidase-mediated metabolism, in cells, and potentially, without this reactive oxygen intermediate, cellular functioning would be limited. In addition, the Km for the catalatic activity of catalase is >10 mm, therefore, at low intracellular concentrations of hydrogen peroxide, this reaction is not kinetically favored, and it is assumed that peroxidases such as glutathione peroxidase or the recently discovered l-Cys peroxiredoxins effectively lower intracellular concentrations of hydrogen peroxide (10Rhee S.G. Chang T.S. Bae Y.S. Lee S.R. Kang S.W. J. Am. Soc. Nephrol. 2003; 14: S211-S215Crossref PubMed Google Scholar). In the present studies, we demonstrated that, in addition to the hydrogen peroxide degrading catalatic activity, mammalian catalases possess an oxidase activity. We found that several peroxidase substrates also function as substrates for mammalian catalase in the absence of hydrogen peroxide. This enzymatic activity is oxygen-dependent and inhibited by classic catalase inhibitors, including sodium azide and 3-amino-1,2,4-triazole as well as several dietary constituents thought to be antioxidants such as indole-3-carbinol and epigallocatechin-3-gallate, a constituent of green tea. Mammalian cells were found to contain endogenous substrates for the enzyme, in particular, indole, an intermediate in tryptophan biosynthesis and β-phenylethylamine, a neurotransmitter precursor. Taken together, these data suggest that the oxidase activity of catalase may be functionally important in cellular metabolism. Enzymes and Chemicals—Catechol (1,2-dihydroxybenzene), ferulic acid (4-hydroxy-3-methoxycinnamic acid), and 1,8-diaminonaphthalene were from Aldrich Chemical Co., 10-acetyl-3,7-dihydroxyphenoxazine, 2′,7′-dichlorofluorescein and resorufin (3H-phenoxazin-3-one) 2The abbreviations used are: resorufin3H-phenoxazin-3-oneABTS2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid)ATZ3-amino-1,2,4-triazoleDCFHdichlorofluoresceinDMB(dimethoxybenzidine) o-dianisidinetTBSTris-buffered saline with 0.1% Tween 20. from Molecular Probes (Eugene, OR), and polyclonal anti-catalase antibodies from Abcam Ltd. (Cambridge, UK). Horseradish peroxidase-conjugated goat anti-rabbit IgG was from Bio-Rad. n-Octyl-β-d-glucoside was from Calbiochem. Purified bovine and mouse liver catalase, twice crystallized bovine liver catalase, and all other chemicals were from Sigma, unless otherwise indicated. Purified bovine liver catalase was also obtained from Worthington Biochemical Corp. (Lakewood, NJ). Re-purified bovine liver and keratinocyte catalase were prepared as previously described (11Heck D.E. Vetrano A.M. Mariano T.M. Laskin J.D. J. Biol. Chem. 2003; 278: 22432-22436Abstract Full Text Full Text PDF PubMed Scopus (283) Google Scholar). 3H-phenoxazin-3-one 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) 3-amino-1,2,4-triazole dichlorofluorescein (dimethoxybenzidine) o-dianisidine Tris-buffered saline with 0.1% Tween 20. Cell Culture—HA-1 and catalase-overexpressing OC5 Chinese hamster fibroblasts were obtained from Douglas Spitz at the University of Iowa (Iowa City, IA). All cells were maintained in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum, penicillin (100 units/ml) and streptomycin (100 μg/ml) at 37 °C in 5% CO2 in a humidified incubator. All were obtained from lysates, cells were from in of saline and × Cell were and in saline supplemented with cells were for a were at °C catalase oxidase activity reaction pH and catalase in a reaction of cell lysates, of was The reaction was by the addition of of otherwise all were at for of the resorufin was an a and a resorufin was by at In (100 (100 or were used as and was by increases in at and and by pH studies, the reaction was sodium pH and sodium pH and pH and and sodium pH and and was the or the bovine as the were as previously described (11Heck D.E. Vetrano A.M. Mariano T.M. Laskin J.D. J. Biol. Chem. 2003; 278: 22432-22436Abstract Full Text Full Text PDF PubMed Scopus (283) Google Scholar). containing catalase were 10% and then with 5% bovine in saline with 0.1% Tween for were with anti-catalase antibodies at °C by peroxidase-conjugated antibodies for at were and Difference and spectra were by the substrates to a which catalase in pH in with catalase, were with a at and at the in the oxidase activity of catalase was was a of catalase for to the of oxygen. that 10-acetyl-3,7-dihydroxyphenoxazine was and the was to from the catalase were into Difference spectra were catalase without substrate as a catalase was then and the spectra were catalase without substrate as a was with concentrations of 10-acetyl-3,7-dihydroxyphenoxazine in reaction and of resorufin was for was a was used to reaction A.M. Biochem. PubMed Scopus Google Scholar). with a oxygen was used to oxygen by catalase oxidase. were at 37 °C in pH of Catalase in or Cell were from and at × for containing the cells were and in saline the with intact cells, 10-acetyl-3,7-dihydroxyphenoxazine was added to the of the cell (100 were then in in of a and the as described of the of 10-acetyl-3,7-dihydroxyphenoxazine was used as the substrate to the oxidase activity of catalase, because it is a electron which resorufin for highly and enzyme (see 1). activity was in purified catalases obtained from several including mouse and bovine mouse and and hamster fibroblasts and and data not (11Heck D.E. Vetrano A.M. Mariano T.M. Laskin J.D. J. Biol. Chem. 2003; 278: 22432-22436Abstract Full Text Full Text PDF PubMed Scopus (283) Google Scholar). This activity was also detected in highly purified enzyme including twice crystallized bovine catalase and bovine liver catalase (Fig. (11Heck D.E. Vetrano A.M. Mariano T.M. Laskin J.D. J. Biol. Chem. 2003; 278: 22432-22436Abstract Full Text Full Text PDF PubMed Scopus (283) Google of the oxidase activity of activity of catalase was at by the formation of the resorufin 10-acetyl-3,7-dihydroxyphenoxazine as the time-dependent oxidase activity of of concentrations of twice crystallized catalase enzyme activity. of pH catalase oxidase activity. The enzyme was in in pH from to of of The enzyme activity was at or reaction and then to by the of catalase oxidase activity. Catalase was for at the to and then for oxidase activity. of catalase oxidase activity. of In the formation of a at corresponding to resorufin was (Fig. results were found in (Fig. Using bovine liver catalase, the oxidase activity was Catalase oxidase activity was found to be with to and and and was with an optimum from pH to (Fig. The of the reaction was also to in these the of oxidase activity the was and the was to (Fig. and activity was by of of the enzyme activity at °C (Fig. This is to the of the catalatic activity of the enzyme P. PubMed Scopus Google Scholar). and reaction inhibited catalase oxidase activity (Fig. that the reaction was In addition, Fig. that the catalase oxidase reaction oxygen. these we found that of molecular catalase was for of The catalase oxidase activity was by the addition of hydrogen peroxide (100 to to to the reaction or the addition of the substrate, that the reaction was from the peroxidase reaction not activity was also by the addition of including NADPH, or not of 10-acetyl-3,7-dihydroxyphenoxazine by catalase was and The for the substrate were 2.4 × 10-4 and × 10-5 and the Vmax 4.7 × 10-5 and × 10-5 for bovine and mouse liver catalases, the bovine liver catalase, the for the reaction was and the was × Taken these data that mammalian catalases a previously oxidase activity that is of hydrogen peroxide. In of studies we catalase oxidase activity was in these studies, we used a cell and a for to hydrogen peroxide Spitz Google Scholar). OC5 cells catalase the cells J. Cell Physiol. 1993; PubMed Scopus Google Scholar) (Fig. We found that 10-acetyl-3,7-dihydroxyphenoxazine was oxidized in intact and cells as well as in cell (Fig. activity was in cells catalase and in from these cells, a with the catalase activity in these of Catalase and oxidized intermediate of catalase be by P. Chem. Google Scholar, B. Biochem. J. PubMed Scopus Google Scholar). of these provides important into the reaction Catalase reaction in the of as well as in the we the of the catalase oxidase activity Difference spectroscopy to the catalase oxidase reaction mechanism and to the of and As with 10-acetyl-3,7-dihydroxyphenoxazine as the substrate, formation of resorufin was in the spectra (Fig. We also found that substrate to catalase in the heme of the the of 10-acetyl-3,7-dihydroxyphenoxazine to bovine liver catalase in a time-dependent formation of a at and a at (Fig. The optimum for this to the mouse liver catalase, the was at and the at not The in the of catalase at is the of a in ferric heme with a corresponding in an oxyferryl species as by the time-dependent of the at B. Biochem. J. PubMed Scopus Google Scholar). We suggest that this species is compound or compound II-like B. Biochem. J. PubMed Scopus Google Scholar). the it that substrate by catalase to the formation of this intermediate. These data with that the oxidase reaction utilizes molecular oxygen (Fig. also that the catalase oxidase activity in the state of the of Catalase and studies demonstrated that inhibit the activity of catalase as well as a of oxidases Biochemistry. PubMed Scopus Google Scholar, PubMed Scopus Google Scholar, J. Biochem. PubMed Scopus Google Scholar, A.M. PubMed Google Scholar). was found to be a highly effective of catalase oxidase activity. revealed that was an with a of × 10-4 (Fig. and to function by to the not to This would catalase oxidase without its for the It be that by not the of catalase that its action is not in catalase heme not the classic catalase inhibitors sodium azide and were found to be inhibitors of catalase oxidase activity, at high concentrations × and × m, data not of electron to inhibit catalase oxidase were as inhibitors of bovine liver catalase oxidase 10-acetyl-3,7-dihydroxyphenoxazine as the substrate as described and in a a were as inhibitors of bovine liver catalase oxidase 10-acetyl-3,7-dihydroxyphenoxazine as the substrate as described and 10-acetyl-3,7-dihydroxyphenoxazine is also a peroxidase substrate M. N. Biochem. 1997; PubMed Scopus Google we other peroxidase substrates, including and as substrates for catalase oxidase activity Biochem. PubMed Scopus Google Scholar, Biol. 1999; PubMed Scopus Google Scholar) (see for Catalase oxidized all of these (Fig. These data that catalase has substrate a with the substrate of peroxidases B. The of and other of Scholar). We the oxidase substrates with 10-acetyl-3,7-dihydroxyphenoxazine for catalase activity. All were found to inhibit the of 10-acetyl-3,7-dihydroxyphenoxazine of these revealed that these catalase oxidase substrates were inhibitors of the reaction (Fig. and data not was the effective × 10-5 by × 10-4 and × peroxidase substrates, including × o-dianisidine × 10-5 × 10-4 × 10-4 and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) × 10-4 were also effective inhibitors of the reaction and not is of because it is a neurotransmitter precursor PubMed Scopus Google Scholar). that is a peroxidase substrate, M. A. Biol. 1997; 23: PubMed Scopus Google was found to be a of catalase oxidase activity × 10-4 10-acetyl-3,7-dihydroxyphenoxazine was used as the substrate (Fig. and This that it has for catalase and the the presence of substrate not the of and These data that the peroxidase substrates function to inhibit catalase oxidase by mechanism of of catalase oxidase is from is a that is a well Toxicol. PubMed Scopus Google Scholar). including and were all effective inhibitors of 10-acetyl-3,7-dihydroxyphenoxazine by catalase Fig. and data not These were all inhibitors with to was the active with a of × 10-5 These data the substrate of catalase oxidase and the enzyme activity as potentially important for It is of that the of the This was to the electron which to with activity of in the catalase oxidase of and catalase oxidase and were as inhibitors of bovine liver catalase oxidase as described and in a and were as inhibitors of bovine liver catalase oxidase as described and to the substrate 10-acetyl-3,7-dihydroxyphenoxazine, the also the heme spectra in catalase (Fig. and data not Difference spectroscopy of the reaction of o-dianisidine with the enzyme revealed a time-dependent in ferric by the formation of a at and the formation of an oxyferryl by a that at (Fig. o-dianisidine in the of and by the of an at of formation of compound (Fig. and compound B. Biochem. J. PubMed Scopus Google Scholar). These data that the catalase oxidase reaction with substrates is to reaction and also known substrates for M. M. 2003; PubMed Scopus Google Scholar, A. J. PubMed Scopus Google a of which molecular oxygen to oxidize and Biochemistry. PubMed Scopus Google Scholar). to peroxidase substrates, the laccase substrates 1,8-diaminonaphthalene and ferulic acid acid), and the vanillic acid acid) also inhibit 10-acetyl-3,7-dihydroxyphenoxazine All were inhibitors with to 10-acetyl-3,7-dihydroxyphenoxazine with of × 10-4 m, × 10-4 m, and × 10-4 m, and not The dietary constituent the in green was also an effective of catalase oxidase × 10-4 and peroxidases also oxidize A. A. J. PubMed Scopus Google Scholar, PubMed Scopus Google we the of the dietary constituents indole, indole-3-carbinol, and the catalase oxidase activity. Each was found to be a of catalase oxidase with of × 10-4 m, × m, and × 10-5 m, and not Taken together, that a of as well as dietary and substrates inhibitors for the oxidase activity of Our data that mammalian catalase possesses a previously oxidase activity. This activity was in catalases from including bovine and mouse mouse and as well as in highly purified of the enzyme, including catalase and catalase from bovine In addition, this activity also be detected in intact cells and cell intact cells possess this activity that it may a role in cellular metabolism. This is by that at two endogenous of catalase oxidase activity (see Our that the oxidase activity substrate and cofactor as well as reaction that catalase oxidase activity is from its previously catalatic and peroxidatic In this the enzymatic activity, which was not the addition of hydrogen peroxide or any to the oxidase activity found in B. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In addition, the catalatic activity of catalase, which not classic to the high reaction and of the enzyme at high hydrogen peroxide concentrations P. PubMed Scopus Google Scholar, B. Biochem. Biophys. PubMed Scopus Google catalase oxidase activity was and The of the enzyme for 10-acetyl-3,7-dihydroxyphenoxazine 2.4 × 10-4 is for its catalatic metabolism of hydrogen peroxide × However, hydrogen peroxide is 10-acetyl-3,7-dihydroxyphenoxazine × × Our studies that the of of 10-acetyl-3,7-dihydroxyphenoxazine is to the metabolism of carcinogens by enzymes Rev. 36: PubMed Scopus Google Scholar). It is important to that 10-acetyl-3,7-dihydroxyphenoxazine is an substrate, and it is that substrates be including endogenous The reaction for the catalase catalatic and peroxidatic been In catalase, in a high ferric state both the catalatic and peroxidatic to be in a of the enzyme with a molecule of hydrogen peroxide to the formation of compound I (Fig. This intermediate is by electron generating an oxyferryl species and a porphyrin radical. In the second of the catalatic two from an molecule of hydrogen peroxide used to convert the enzyme from the compound I state to the ferric to the of oxygen and the formation of catalase compound I may oxidize molecular weight alcohols the peroxidatic of catalase (Fig. In addition, for in the presence of hydrogen peroxide, compound I, in a electron may be to compound a In compound with molecule of hydrogen peroxide to compound or with electron including NADPH and be to the ferric state (Fig. In it is thought that NADPH may as well as the accumulation of compound (7Kirkman H.N. Rolfo M. Ferraris A.M. Gaetani G.F. J. Biol. Chem. 1999; 274: 13908-13914Abstract Full Text Full Text PDF PubMed Scopus (215) Google Scholar, H.N. Gaetani G.F. J. Biol. Chem. Full Text PDF PubMed Google Scholar). Difference spectroscopy has been used to both the catalatic and peroxidase of of the catalase oxidase activity that the reaction heme mechanism by electron to the formation of compound interactions of heme and molecular is with (Fig. This is by that, in a to that in heme of catalase oxidase activity in formation of a at Biochem. J. PubMed Scopus Google Scholar) (Fig. In this endogenous or electron present in cells convert the enzyme to the ferric Our that NADPH not compound formation because suggest that the of catalase oxidase activity is of this of oxygen during the reaction and the of the compound spectra we one to that the oxidase activity of catalase, the peroxidase activity, may involve electron In addition, data suggest that, in the presence of involving of an electron by the substrate and of molecular oxygen with the heme in the formation of an oxyferryl and a of this and accumulation of a compound II-like intermediate. We that, in a potentially by a the substrate is oxidized and the enzyme to the Our that of oxygen was for of such a This mechanism may with an of potentially by the formation of However, at the present the precise mechanism of the oxidase reaction is unclear, because the of the reaction and as with the of the oxidase activity of catalase exhibits substrate substrates, in addition to 10-acetyl-3,7-dihydroxyphenoxazine, were and These substrates were found to be inhibitors of catalase with to 10-acetyl-3,7-dihydroxyphenoxazine, that function by the of 10-acetyl-3,7-dihydroxyphenoxazine is it to and inhibitors of catalase of which may also be substrates of the all inhibitors, which a of of which also peroxidase substrates, were found to be with to These include and a laccase which from a substrate to oxidases that, to also known to substrate Biochemistry. PubMed Scopus Google Scholar). These the of substrate to the precise the catalase for its oxidase activity is the of peroxidases and been well characterized J. Biol. Scopus Google Scholar, M. Biophys. Biol. 1999; PubMed Scopus Google Scholar). These enzymes a substrate and to the of It is that catalase has a that it to the of the of substrates for the oxidase the of bovine liver catalase, we one such This potential is to the of catalase, the heme and by and (Fig. In this this is thought to be by inhibitors of the catalase catalatic including acid M. Biophys. Biol. 1999; PubMed Scopus Google Scholar). However, such as the to well into this as by the that it catalase oxidase by a was that is a of the catalase oxidase to catalase, is thought to the enzyme an oxidized intermediate J. Biol. Scopus Google Scholar, M. Biophys. Biol. 1999; PubMed Scopus Google Scholar). in hydrogen a for in the for peroxide, and in the has been J. Biol. Scopus Google Scholar). The potential for oxidase substrates that we this Our in with the that a compound II-like state is during catalase oxidase activity, suggest that substrate is by formation of an oxyferryl intermediate and the cation in this of the of the by catalase provides into the reaction It was that was an the activity of these and electron We that by the presence of the in the of catalase, a potentially important in the substrates with the the Taken with of catalase oxidase substrates to a to the the substrates with and (Fig. of is that and several dietary of which active in the catalase oxidase of these including and indole-3-carbinol, also peroxidase It is well that peroxidases the to carcinogens such as PubMed Scopus Google Scholar). electron of reactive which to carcinogenic PubMed Scopus Google Scholar, B. The of and other of Scholar). it is catalase of results in the formation of carcinogenic The activity of and ferulic acid, as well as epigallocatechin-3-gallate, is is that several dietary constituents known to inhibit the carcinogenic including ferulic acid, indole-3-carbinol, and the green constituent A. M. J. PubMed Scopus Google Scholar, Rev. Google Scholar, Rev. PubMed Scopus Google were active in the catalase oxidase that, catalase oxidase is important in carcinogens such as the ability of the dietary constituents to in this process may be important in activity. endogenous were active in catalase oxidase the tryptophan indole, and the neurotransmitter as were also in of fibroblasts and that inhibit of 10-acetyl-3,7-dihydroxyphenoxazine by M. D. M. D. and J. D. These may be substrates of catalase oxidase and suggest that the enzyme is to be functionally important in cellular metabolism. It to be dietary active in the catalase oxidase the action of endogenous in In we characterized a novel oxidase activity of mammalian This activity, which is from the catalatic and peroxidatic of the enzyme, utilizes substrates and inhibitors, including and endogenous The oxidase reaction requires molecular oxygen and to electron a compound II-like intermediate. studies to heme in catalase A. P. Biochemistry. PubMed Scopus (67) Google a that a mechanism of oxygen in the mammalian catalase oxidase has been that catalase to cellular hydrogen peroxide to molecular weight electron such as Our studies that the enzyme possesses in metabolism studies to the and reaction mechanism for the oxidase reaction in catalase and to the role of this enzymatic activity in cellular metabolism.