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At least 919 records · Page 51Linked to original sources
PubMed2001

Role of extracellular peroxidase in the superoxide production by wheat root cells.

Extracellular peroxidase has been shown to contribute to superoxide production in wounded wheat (Triticum aestivum L. cv. Ljuba) root cells. The superoxide-synthesizing system of root cells was considerably inhibited by KCN and NaN3 and activated by MnCl2 and H2O2. Treatment of roots with salicylic acid and a range of di- and tri-carbonic acids (malic, citric, malonic, fumaric, and succinic acids) stimulated superoxide production in both root cells and extracellular solution. The H2O2-stimulated superoxide production in the extracellular solution was much higher when roots were preincubated with salicylic or succinic acid. Exogenous acids enhanced peroxidase activity in the extracellular solution. Pretreatment of root cells with the detergents trypsin and sodium dodecyl sulfate had similar effects on the peroxidase activity. Significant inhibition of both superoxide production and peroxidase activity by diphenylene iodonium suggests that the specificity of the latter as an inhibitor of NADPH oxidase is doubtful. Results obtained indicate that extra-cellular peroxidase is involved in the superoxide production in wheat root cells. The mobile form of peroxidase can be readily secreted to the apoplastic solution and serve as an emergency enzyme involved in plant wound response.

Adrenochrome↗
PubMed1986

Characterisation of an antiserum and development of an ELISA for glutathione peroxidase.

Sheep red blood cells were fractionated by ion exchange and gel filtration chromatography to yield glutathione peroxidase approximately 99% pure. An antiserum against glutathione peroxidase was raised in the rabbit. The antiserum has been shown to cross-react with both bovine and human glutathione peroxidase by double diffusion. An enzyme linked immunosorbent assay has been developed for glutathione peroxidase which detected 6.15 X 10(-5) IU of the enzyme. The antiserum has also been shown to be effective in the detection of glutathione peroxidase immobolised on strips of nitrocellulose, subsequent to sodium dodecyl sulphate polyacrylamide gel electrophoresis, by second antibody conjugate. Avidin-biotin was also used to detect nitrocellulose immobolised enzyme. These techniques provide an alternative highly sensitive and specific means of assaying glutathione peroxidase which is not dependent on the lability of enzymatic activity nor the chemical specificity of the assay.

Animals↗
PubMed1976

Intracellular distinction between peroxidase and catalase in exocrine cells of rat lacrimal gland: a biochemical and cytochemical study.

The lacrimal gland (Glandula orbitalis externa) of rat contains both peroxidase and catalase and was used as a model for biochemical and cytochemical distinction between peroxidase and catalase. Both enzymes were isolated by ammonium sulfate precipitation from tissue homogenates, and the effects of fixation with glutaraldehyde and various conditions of incubation were investigated colorimetrically using DAB as hydrogen donor. The lacrimal gland peroxidase is strongly inhibited by glutaraldehyde treatment. In contrast, for catalase the fixation with glutaraldehyde is the prerequistie for demonstration of its peroxidatic activity. The maximal peroxidatic activity was obtained after treatment of catalase with 3% glutaraldehyde, higher concentrations being inhibitory. For lacrimal gland peroxidase, the maximal rate of oxidation of DAB is at pH 6.5, whereas for catalase it is at pH 10.5. The optimal concentration of H2O2 for lacrimal gland peroxidase is at 10(-3)M and for peroxidatic activity of catalase at 10(-1)M. These optimal conditions obtained biochemically were applied to tissue sections of rat lacrimal gland. After the fixation of tissue with a low concentration of glutaraldehyde and incubation in the DAB medium at neutral pH containing 10(-3)M H2O2 (Peroxidase medium), the reaction product was localized in the cisternae of the rough endoplasmic reticulum, in elements of the Golgi apparatus, and in secretory granules. After the fixation of tissue with 3% glutaraldehyde and incubation in the DAB-medium containing 10(-1)M H2O2 and at pH 10.5 (catalase medium), the staining in the endoplasmic reticulum, the Golgi-apparatus and in secretory granules was completely inhibited and reaction product was localized exclusively in small (0.2-0.5 mu) particles similar to small peroxisomes described in various other cell-types.

3,3'-Diaminobenzidine↗
PubMed1979

Analysis of mammary tumors for cytochemical evidence of endogenous mammary peroxidase.

The purpose of this study was to determine whether or not endogenous mammary peroxidase can serve as a cytochemical marker to distinguish ovarian hormone-dependent from ovarian hormone independent mammary tumors. Spontaneous mammary tumors arising in virgin C3H and GR mice (hormone independent tumors) and hormone-dependent mammary tumors arising during pregnancy in GR mice were examined. None of these tumors contained mammary peroxidase. Mammary tumors induced in Sprague-Dawley rats with methylnitrousourea (MNU) and dimethylbenzanthracene (DMBA) were also examined. These tumors included hormone-dependent and hormone independent ones. Several of the DMBA-induced hormone-dependent tumors contained a few peroxidase-positive cells, but the hormone independent tumors were negative. All of the MNU-induced tumors examined were negative for mammary peroxidase. Twenty human breast tumors (malignant and non-malignant) removed from women at surgery, were also negative for mammary peroxidase. Our results indicate that endogenous mammary peroxidase cannot be used to distinguish hormone-dependent from hormone independent mammary tumors.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1991

Synthesis and properties of lignin peroxidase from Streptomyces viridosporus T7A.

The production of lignin peroxidase by Streptomyces viridosporus T7A was studied in shake flasks and under aerobic conditions in a 7.5-L batch fermentor. Lignin peroxidase synthesis was found to be strongly affected by catabolite repression. Lignin peroxidase was a non-growth-associated, secondary metabolite. The maximum lignin peroxidase activity was 0.064 U/mL at 36 h. In order to maximize lignin peroxidase activity, optimal conditions were determined. The optimal incubation temperature, pH, and substrate (2,4-dichlorophenol) concentration for the enzyme assays were 45 degrees C, 6, and 3 mM, respectively. Stability of lignin peroxidase was determined at 37, 45, and 60 degrees C, and over the pH range 4-9.

Enzyme Repression↗
PubMedDate not supplied

Abnormalities of blood selenium and glutathione peroxidase activity in patients with acquired immunodeficiency syndrome and aids-related complex.

Severe protein-calorie malnutrition is common in patients with AIDS and could contribute to the progressive deterioration characteristic of that disease. Selenium deficiency could also have a negative impact on immune function and other organ functions vital for recovery from infectious diseases. Therefore, to assess any role for selenium in AIDS we determined plasma and erythrocyte selenium levels and glutathione peroxidase activity in 13 patients with AIDS compared to 8 patients with AIDS-related complex (ARC) and 14 healthy controls. Plasma selenium levels were significantly reduced in AIDS patients compared to controls (p less than .0001) and to ARC (p less than .02). Erythrocyte selenium levels in both AIDS and ARC were also reduced compared to controls (p less than .02), but not to each other. Glutathione peroxidase activity in AIDS was 28.9 +/- 1.4 U/g Hb vs 38.4 +/- 6.9 in ARC (p = NS) and 52.3 +/- 1.7 in controls (p less than .0001 vs AIDS; p less than .02 vs ARC). When all groups were combined, there were significant correlations between total lymphocyte count and both plasma selenium (r = .53; p less than .002) and erythrocyte glutathione peroxidase activity (r = .65; p less than .0001). In addition, strong correlations were noted between plasma selenium and serum albumin (r = .68; p less than .0001), plasma selenium and glutathione peroxidase (r = .77; p less than .0001), and glutathione peroxidase and hematocrit (r = .66; p less than .0001). In AIDS or ARC, no correlations between selenium with disease duration or weight loss were present. We conclude that, in comparison to normals, patients manifesting infection with human immunodeficiency virus have evidence of selenium deficiency as determined by diminished plasma and erythrocyte levels and glutathione peroxidase activity. These abnormalities are most marked in patients with AIDS, but are also present in patients with AIDS-related complex. Selenium deficiency has important implications for the progression and pathogenesis of clinical disease in AIDS.

AIDS-Related Complex↗
PubMed2000

Kinetics and thermodynamics of peroxidase- and laccase-catalyzed oxidation of N-substituted phenothiazines and phenoxazines.

Steady-state and single-turnover kinetics for the oxidation of the N-substituted phenothiazines (PTs) and phenoxazines (POs) catalyzed by fungal Coprinus cinereus peroxidase and Polyporus pinsitus laccase were investigated at pH 4-10. In the case of peroxidase, an apparent bimolecular rate constant (expressed as k(cat)/K(m)) varied from 1 x10(7)M(-1)s(-1) to 2.6 x 108 M(-1)s(-1) at pH 7.0. The constants for PO oxidation were higher in comparison to PT. pH dependence revealed two or three ionizable groups with pKa values of 4.9-5.7 and 7.7-9.7 that significantly affected the activity of peroxidase. Single-turnover experiments showed that the limiting step of PT oxidation was reduction of compound II and second-order rate constants were obtained which were consistent with the constants at steady-state conditions. Laccase-catalyzed PT and PO oxidation rates were lower; apparent bimolecular rate constants varied from 1.8x 10(5) M(-1) s(-1) to 2.0 x 10(7) M(-1) s(-1) at pH 5.3. PO constants were higher in comparison to PT, as was the case with peroxidase. The dependence of the apparent bimolecular constants of compound II or copper type 1 reduction, in the case of peroxidase or laccase, respectively, was analyzed in the framework of the Marcus outer-sphere electron-transfer theory. Peroxidase-catalyzed reactions with PT, as well as PO, fitted the same hyperbolic dependence with a maximal oxidation rate of 1.6 x 10(8)M(-1)s(-1) and a reorganization energy of 0.30 eV. The respective parameters for laccase were 5.0 x 10(7) M(-1) s(-1) and 0.29 eV.

Antiprotozoal Agents↗
PubMed2006

Peroxidase activity of selenoprotein GrdB of glycine reductase and stabilisation of its integrity by components of proprotein GrdE from Eubacterium acidaminophilum.

The anaerobe Eubacterium acidaminophilum has been shown to contain an uncharacterized peroxidase, which may serve to protect the sensitive selenoproteins in that organism. We purified this peroxidase and found that it was identical with the substrate-specific "protein B"-complex of glycine reductase. The "protein B"-complex consists of the selenocysteine-containing GrdB subunit and two subunits, which derive from the GrdE proprotein. The specific peroxidase activity was 1.7 U (mg protein)(-1) with DTT and cumene hydroperoxide as substrates. Immunoprecipitation experiments revealed that GrdB was important for DTT- and NADH-dependent peroxidase activities in crude extracts, whereas the selenoperoxiredoxin PrxU could be depleted without affecting these peroxidase activities. GrdB could be heterologously produced in Escherichia coli with coexpression of selB and selC from E. acidaminophilum for selenocysteine insertion. Although GrdB was sensitive to proteolysis, some full-size protein was present which accounted for a peroxidase activity of about 0.5 U (mg protein)(-1) in these extracts. Mutation of the potentially redox-active UxxCxxC motif in GrdB resulted in still significant, but decreased activity. Heterologous GrdB was protected from degradation by full-length GrdE or by GrdE-domains. The GrdB-GrdE interaction was confirmed by copurification of GrdE with Strep-tagged GrdB. The data suggest that GrdE domains serve to stabilise GrdB.

Amino Acid Oxidoreductases↗
PubMed2001

Effect of enzyme impurities on phenol removal by the method of polymerization and precipitation catalyzed by Coprinus cinereus peroxidase.

The removal of phenol by peroxidase-catalyzed polymerization was examined using the Coprinus cinereus peroxidases at different levels of impurity with respect to contamination. The phenol removal efficiency was improved by lowering the peroxidase purity. Acidic and high molecular weight proteins present as impurities in the peroxidase solution had some positive effect on the phenol-polymerizing reaction. The residual enzyme activity, either only in the solution or both in the solution and on the precipitate during the polymerizing reaction, was measured. The results indicate that the main effect of impurities in the peroxidase solution was the suppression of the adsorption of peroxidase molecules on the polymerized precipitate.

Adsorption↗
PubMed2003

Differential distribution of ascorbic acid, peroxidase activity, and hydrogen peroxide along the root axis in Allium cepa L. and its possible relationship with cell growth and differentiation.

In this paper we show an asymmetrical distribution of apoplastic and symplastic ascorbic acid content, peroxidase activities and hydrogen peroxide along the root axis in Allium cepa L. For most of these metabolites, a marked gradient from the root apex to the onion base was observed and was different for apoplastic and symplastic compartments. In total homogenates, ascorbic acid content was higher in the zones closer to the apex and decreased towards the root base. However, an opposite pattern was observed in the apoplastic fraction. Peroxidase activities with guaiacol, ferulic acid, ascorbic acid, and coniferyl alcohol were also different depending on the evaluated zone and the fraction used (apoplastic or symplastic). In general, each activity had a specific and unique pattern. Immunodetection of peroxidase proteins in Western blots using anti-horseradish peroxidase and anti-ascorbate peroxidase antibodies revealed different bands at the different zones of the root. Hydrogen peroxide was detected by electron microscopy and was mainly found in cell walls of epidermis (or rhizodermis), meristem, and elongating cells. The number of cell walls showing hydrogen peroxide decreased dramatically towards the root base. The results suggest that the different zones of the root show specific requirements for ascorbic acid and hydrogen peroxide. Also, each fragment of the root seems to express specific peroxidase proteins. Different processes that take place at every part of the root, as cell proliferation and elongation near the root apex and gradual lignification and differentiation towards the root base are the key to explain the results.

Ascorbic Acid↗
PubMed2005

Oxidase reaction of the hybrid Mn-peroxidase of the fungus Panus tigrinus 8/18.

The hybrid Mn-peroxidase of the fungus Panus tigrinus 8/18 oxidized NADH in the absence of hydrogen peroxide, this being accompanied by the consumption of oxygen. The reaction of NADH oxidation started after a period of induction and completely depended on the presence of Mn(II). The reaction was inhibited in the presence of catalase and superoxide dismutase. Oxidation of NADH by the enzyme or by manganese(III)acetate was accompanied by the production of hydrogen peroxide and superoxide radicals. In the presence of NADH, the enzyme was transformed into a catalytically inactive oxidized form (compound III), and the latter was inactivated with bleaching of the heme. The substrate of the hybrid Mn-peroxidase (Mn(II)) reduced compound III to yield the native form of the enzyme and prevented its inactivation. It is assumed that the hybrid Mn-peroxidase used the formed hydrogen peroxide in the usual peroxidase reaction to produce Mn(III), which was involved in the formation of hydrogen peroxide and thus accelerated the peroxidase reaction. The reaction of NADH oxidation is a peroxidase reaction and the consumption of oxygen is due to its interaction with the products of NADH oxidation. The role of Mn(II) in the oxidation of NADH consisted in the production of hydrogen peroxide and the protection of the enzyme from inactivation.

Catalase↗
PubMed2006

Cloning, characterization and localization of three novel class III peroxidases in lignifying xylem of Norway spruce (Picea abies).

Plant class III peroxidases (POXs) take part in the formation of lignin and maturation of plant cell walls. However, only a few examples of such peroxidases from gymnosperm tree species with highly lignified xylem tracheids have been implicated so far. We report here cDNA cloning of three xylem-expressed class III peroxidase encoding genes from Norway spruce (Picea abies). The translated proteins, PX1, PX2 and PX3, contain the conserved amino acids required for heme-binding and peroxidase catalysis. They all begin with putative secretion signal propeptide sequences but diverge substantially at phylogenetic level, grouping to two subclusters when aligned with other class III plant peroxidases. In situ hybridization analysis on expression of the three POXs in Norway spruce seedlings showed that mRNA coding for PX1 and PX2 accumulated in the cytoplasm of young, developing tracheids within the current growth ring where lignification is occurring. Function of the putative N-terminal secretion signal peptides for PX1, PX2 and PX3 was confirmed by constructing chimeric fusions with EGFP (enhanced green fluorescent protein) and expressing them in tobacco protoplasts. Full-length coding region of px1 was also heterologously expressed in Catharanthus roseus hairy root cultures. Thus, at least the spruce PX1 peroxidase is processed via the endoplasmic reticulum (ER) most likely for secretion to the cell wall. Thereby, PX1 displays correct spatiotemporal localization for participation in the maturation of the spruce tracheid secondary cell wall.

Amino Acid Sequence↗
PubMed2006

Examination of the biological effects of high anionic peroxidase production in tobacco plants grown under field conditions. I. Insect pest damage.

At least 25 wild type and high peroxidase tobacco Nicotiana tabacum L. plants were examined semiweekly over several weeks for pest insect distribution and damage in a 2 year field study. Incidence and/or severity of naturally occurring caterpillar damage (dingy cutworm (Feltia ducens Walker), black cutworm (Agrotis ipsilon (Hufnagel), tobacco hornworm (Manduca sexta L.), and false tobacco budworm (= corn earworm Helicoverpa zea (Boddie)) was significantly reduced at several sample dates for high peroxidase vs. wild type plants. These results parallel those of prior laboratory studies with caterpillars. The number of adult whiteflies (Trialeurodes vaporariorum (Westwood) per plant was significantly reduced on high peroxidase compared to wild type plants on most sample dates in both years. The number of plants with leaves containing >100 aphids (primarily Myzus persicae Sulzer) per leaf on high peroxidase plants was significantly lower that on wild type plants after an equivalent invasion period in both years. A significantly higher proportion of aphids were found dead on leaf five of high peroxidase compared to wild type plants at most sample dates in both years. These results indicate that high peroxidase plants have resistance to a wide range of insects, implicating this enzyme as a broad range resistance mechanism.

Animals↗
PubMed1985

Purification and characterization of an extracellular Mn(II)-dependent peroxidase from the lignin-degrading basidiomycete, Phanerochaete chrysosporium.

A Mn(II)-dependent peroxidase found in the extracellular medium of ligninolytic cultures of the white rot fungus, Phanerochaete chrysosporium, was purified by DEAE-Sepharose ion-exchange chromatography, Blue Agarose chromatography, and gel filtration on Sephadex G-100. Sodium dodecyl sulfate-gel electrophoresis indicated that the homogeneous protein has an Mr of 46,000. The absorption spectrum of the enzyme indicates the presence of a heme prosthetic group. The pyridine hemochrome absorption spectrum indicates that the enzyme contained one molecule of heme as iron protoporphyrin IX. The absorption maximum of the native enzyme (406 nm) shifted to 433 nm in the reduced enzyme and to 423 nm in the reduced-CO complex. Both CN- and N-3 readily bind to the native enzyme, indicating an available coordination site and that the heme iron is high spin. The absorption spectrum of the H2O2 enzyme complex, maximum at 420 nm, is similar to that of horseradish peroxidase compound II. P. chrysosporium peroxidase activity is dependent on Mn(II), with maximal activity attained above 100 microM. The enzyme is also stimulated to varying degrees by alpha-hydroxy acids (e.g., malic, lactic) and protein (e.g., gelatin, albumin). The peroxidase is capable of oxidizing NADH and a wide variety of dyes, including Poly B-411 and Poly R-481. Several of the substrates (indigo trisulfonate, NADH, Poly B-411, variamine blue RT salt, and Poly R-481) are oxidized by this Mn(II)-dependent peroxidase at considerably faster rates than those catalyzed by horseradish peroxidase. The enzyme rapidly oxidizes Mn(II) to Mn(III); the latter was detected by the characteristic absorption spectrum of its pyrophosphate complex. Inhibition of the oxidation of the substrate diammonium 2,2-azino-bis(3-ethyl-6-benzothiazolinesulfonate) (ABTS) by Na-pyrophosphate suggests that Mn(III) plays a role in the enzyme mechanism.

Basidiomycota↗
PubMed1986

Comparison of ligninase-I and peroxidase-M2 from the white-rot fungus Phanerochaete chrysosporium.

Ligninase-I (Mr 42,000-43,000; carbohydrate, 21%) and peroxidase-M2 (Mr 45,000-47,000; carbohydrate, 17%), two representative, hydrogen peroxide-dependent extracellular enzymes produced by ligninolytic cultures of the white-rot fungus Phanerochaete chrysosporium BKM-F-1767, were purified and their properties compared. Spectroscopic studies showed that both native enzymes are heme proteins containing protoporphyrin IX. EPR spectroscopy indicated that iron ions are coordinated with the enzymes' prosthetic groups as high-spin ferriheme complexes. We confirmed reports of others that the ligninase-hydrogen peroxide complex (activated enzyme) reverts to its native state on addition of dithionite or one of the enzyme's substrates (e.g., veratryl alcohol); however, we found that the peroxidase-M2-hydrogen peroxide complex required Mn2+ ions to accomplish a similar cycle. The peroxidase oxidized Mn2+ to a higher oxidation state, and the oxidized Mn acted as a diffusible catalyst able to oxidize numerous organic substrates. Unlike ligninase-I which is found free extracellularly, peroxidase-M2 appears to be associated closely with the fungal mycelium. In its peroxidatic reactions, ligninase-I oxidizes a variety of nonphenolic and phenolic lignin model compounds. In the presence of Mn2+, peroxidase-M2 oxidizes numerous phenolic compounds, especially syringyl (3,5-dimethoxy-4-hydroxyphenyl) and vinyl side-chain substituted substrates. Also, the peroxidase-Mn2+ system (without hydrogen peroxide) expresses oxidase activity against NADPH, GSH, dithiothreitol, and dihydroxymaleic acid, forming hydrogen peroxide at the expense of oxygen. Both enzymes were believed to play roles in lignin degradation, and these are discussed.

Amino Acids↗
PubMed1988

Prostaglandin H synthase: distinct binding sites for cyclooxygenase and peroxidase substrates.

Prostaglandin H synthase has two distinct catalytic activities: a cyclooxygenase activity that forms prostaglandin G2 from arachidonic acid; and a peroxidase activity that reduces prostaglandin G2 to prostaglandin H2. Lipid hydroperoxides, such as prostaglandin G2, also initiate the cyclooxygenase reaction, probably via peroxidase reaction cycle enzyme intermediates. The relation between the binding sites for lipid substrates of the two activities was investigated with an analysis of the effects of arachidonic and docosahexaenoic acids on the reaction kinetics of the peroxidase activity, and their effects on the ability of a lipid hydroperoxide to initiate the cyclooxygenase reaction. The cyclooxygenase activity of pure ovine synthase was found to have an apparent Km value for arachidonate of 5.3 microM and a Ki value (competetive inhibitor) for docosahexaenoate of 5.2 microM. When present at 20 microM neither fatty acid had a significant effect on the apparent Km value of the peroxidase for 15-hydroperoxyeicosatetraenoic acid: the values were 7.6 microM in the absence of docosahexaenoic acid and 5.9 microM in its presence, and (using aspirin-treated synthase) 13.7 microM in the absence of arachidonic acid and 15.7 microM in its presence. Over a range of 1 to 110 microM the level of arachidonate had no significant effect on the initiation of the cyclooxygenase reaction by 15-hydroperoxyeicosatetraenoic acid. The inability of either arachidonic acid or docosahexaenoic acid to interfere with the interaction between the peroxidase and lipid hydroperoxides indicates that the cyclooxygenase and peroxidase activities of prostaglandin H synthase have distinct binding sites for their lipid substrates.

Animals↗
PubMed1990

Axial ligand coordination in intestinal peroxidase.

EPR spectra of intestinal peroxidase are reported for the first time. The resting state of intestinal peroxidase exhibits only a high spin EPR spectrum with pH-dependent rhombicity. Addition of chloride shifts the equilibrium between an acidic and a neutral form of the enzyme. In contrast, resting lactoperoxidase shows EPR spectra of both low spin and high spin species, indicating a different heme environment between these two peroxidases. The high spin signal of lactoperoxidase consists of multiple components; the major component exhibits pH-dependent rhombicity similar to intestinal peroxidase and the equilibrium between the acidic and the neutral forms is also shifted by chloride ion. EPR features of the low spin cyanide complex of intestinal peroxidase and lactoperoxidase are compared with those of other hemeproteins, whose proximal axial ligands are known to be histidine residues. The g-values of the cyanide adducts of the mammalian peroxidases are similar. The relationship between the g-value anisotropy and imidazolate character of the proximal histidine is discussed.

Animals↗
PubMed1992

Purification and characterization of a catalase-peroxidase from the fungus Septoria tritici.

Three classes of heme proteins, commonly designated hydroperoxidases, are involved in the metabolism of hydrogen peroxide: catalases, peroxidases, and catalase-peroxidases. While catalases and peroxidases are widely spread in animals, plants, and microorganisms, catalase-peroxidases were characterized only in prokaryotes. We report here, for the first time, on a catalase-peroxidase in a eukaryotic organism. The enzyme was purified from the fungal wheat pathogen Septoria tritici, and is one of three different hydroperoxidases synthesized by this organism. The S. tritici catalase-peroxidase, designated StCP, is similar to the enzymes previously isolated from the bacteria Rhodobacter capsulatus, Escherichia coli, and Klebsiella pneumoniae, although it is significantly more sensitive to denaturing conditions. In addition to its catalatic activity StCP catalyzes peroxidatic activity with o-dianisidine, diaminobenzidine, pyrogallol, NADH, and NADPH as electron donors. The enzyme is a tetramer with identical subunits of 61,000 Da molecular weight. StCP shows a typical high-spin ferric heme spectrum with a Soret band at 405 nm and a peak at 632 nm, and binding of cyanide causes a shift of the Soret band to 421 nm, the appearance of a peak at 537 nm, and abolition of the peak at 632 nm. Reduction with dithionite results in a decrease in the intensity of the Soret band and its shift to 436 nm, and in the appearance of a peak at 552 nm. The pH optimum is 6-6.5 and 5.4 for the catalatic and peroxidatic activities, respectively. Fifty percent of the apparent maximal activity is reached at 3.4 mM and 0.26 mM for the catalatic and peroxidatic activities, respectively. The enzyme is inactivated by ethanol/chloroform, and is inhibited by KCN and NaN3, but not by the typical catalase inhibitor 3-amino-1,2,4-triazole.

Catalase↗