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PubMed1990

Beta-adrenoceptor control of peroxidase synthesis in nasal glands.

Endogenous peroxidase activity was observed in the cisternae of the rough-surfaced endoplasmic reticulum (r-ER), including the nuclear envelope, Golgi complex, and secretory granules of the cat's nasal glands. A single injection of propranolol resulted in a decrease of peroxidase-positive secretory granules, an increase of electron-lucent granules, and no change in the level of peroxidase activity in the r-ER and Golgi complex at either 5 or 9 hours after the injection. Continuous administration of propranolol over 7 hours led to the disappearance of peroxidase activity from the r-ER and secretory granules. These data would indicate that propranolol inhibits only the synthesis of peroxidase. Twenty minutes after a single injection of isoproterenol, the rate at which the granule content containing the peroxidase reaction product was discharged into the acinar lumen increased sharply. However, 60 minutes after the injection, the secretion rate of peroxidase-positive granules decreased. The same experiment then was repeated, but this time before the isoproterenol was injected, propranolol was administered to the cats. This time no change in peroxidase activity appeared in the acinar cells. It was concluded, therefore, that the stimulation of beta-receptors enhances the synthesis of peroxidase.

Animals↗
PubMed2001

Immunohistochemical detection of human gastrointestinal glutathione peroxidase in normal tissues and cultured cells with novel mouse monoclonal antibodies.

This is the first report to describe the successful detection of human gastrointestinal glutathione peroxidase in normal tissues by Western blotting and immunohistochemical staining techniques. Four hybridoma clones producing monoclonal antibodies (MAbs) against the human gastrointestinal glutathione peroxidase were established from mice immunized with a gastrointestinal glutathione peroxidase-derived peptide. The MAbs did not crossreact with other members of the glutathione peroxidase family, be it cellular glutathione peroxidase, phospholipid hydroperoxide glutathione peroxidase, or extracellular glutathione peroxidase. Although the MAbs were found to react with a 24-kD protein in a Western blotting assay using gastric carcinoma cell extracts as antigen, they did not react with a B-lymphoblastoid cell extract. Immunohistochemical staining showed gastrointestinal glutathione peroxidase localized in the cytoplasm and in the nucleus of gastric carcinoma cells. Moreover, gastrointestinal glutathione peroxidase was detected in tissue extracts of human stomach, small intestine, large intestine, liver, and gallbladder by Western blotting, and its localization was immunohistochemically confirmed in the mucosal epithelia of the basal area of gastric pits and intestinal crypts.

Aged↗
PubMed1989

Inhibition of human thyroid peroxidase gene expression by interleukin 1.

We have already demonstrated the inhibitory effect of interleukin 1 on thyroglobulin gene expression. Recent availability of thyroid peroxidase cDNA has allowed us to investigate the regulation of thyroid peroxidase gene. Therefore, the regulation of thyroid peroxidase mRNA by interleukin 1 in cultured human thyrocytes was investigated. Thyrocytes dispersed from thyroid tissues from patients with Graves' disease were incubated with TSH with or without recombinant human interleukin 1. Unstimulated human thyrocytes did not contain any detectable thyroid peroxidase mRNA, however, TSH-stimulated thyrocytes expressed four thyroid peroxidase mRNA transcripts (4.0, 3.2, 2.1 and 1.7 kb, respectively). Both interleukin 1 alpha and beta inhibited TSH-induced thyroid peroxidase mRNA in a dose responsive manner; 10(3) U/1 interleukin 1 caused maximal suppression of TSH-induced thyroid peroxidase mRNA level to nearly basal levels. Interleukin 1 also inhibited cAMP analogue 8-bromo-cyclic AMP induced thyroid peroxidase mRNA level. In contrast the gamma-actin mRNA hybridization signal was not altered in control or treated cells. These results demonstrate that interleukin 1 directly inhibits TSH-induced thyroid peroxidase gene expression and provide further evidence for a paracrine role of interleukin 1 as a local inhibitor of thyroid hormone synthesis.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1991

Evidence for acute release of thyroid peroxidase during subtotal thyroidectomy.

An immediate reduction of thyroglobulin autoantibodies during subtotal thyroidectomy of thyroglobulin antibody positive patients has previously been shown to indicate an acute release of thyroglobulin into the circulation peroperatively. The aim of the present study was to investigate whether thyroid peroxidase was also released by measuring anti-thyroid peroxidase antibodies by a quantitative and antigen specific method both pre- and postoperatively in patients positive for anti-thyroid peroxidase antibodies. Twelve anti-thyroid peroxidase positive patients (11 females, 1 male) referred for surgery of toxic goitre were studied. Median age was 43 years (range 24-64) and median goitre size 86 g (25-165). All patients had been pretreated with antithyroid drugs and were euthyroid at the time of operation. Anti-thyroid peroxidase was measured before operation, 1-8 h, 10 days, 1-3 months, and 12 months postoperatively by a commercial method (DYNO-test, Henning, Berlin). The median anti-thyroid peroxidase level before operation was 1048 kU/l (range 68-10 517 kU/l) and fell during operation to 0.63 (range 0.37-1.28) (p less than 0.01) of initial concentration without further decrease during the next 1-8 h. The comparative decrease in thyroglobulin antibodies was 0.19 (0-0.88). The anti-thyroid peroxidase level was increasing after 10 days, but did not reach initial level until between 3 and 12 months after surgery. However, in 3 of 10 patients anti-thyroid peroxidase had disappeared after 12 months, all of whom had low levels before operation, whereas anti-thyroid peroxidase was 2-4 times higher than preoperatively in 3 other patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Prostaglandin D2 generation in mouse bone marrow-derived mast cells exposed to dexamethasone is associated with endogenous peroxidase activity.

The appearance of fixative-sensitive peroxidase activity in the nuclear envelope and endoplasmic reticulum of bone marrow-derived mast cells (BMMC) cultured in the presence of 1 microM dexamethasone (DM) for up to 14 days and its relationship with immunologic release of prostaglandin D2 (PGD2) by these cells were studied. Endogenous peroxidase activity, previously shown as a marker of arachidonic acid metabolism in various cell types, was visualized by cell incubation in 3,3' diaminobenzidine-containing solution before glutaraldehyde fixation. PGD2 release was induced by passive sensitization of BMMC with an optimal dose of monoclonal IgE and subsequent challenge with specific a antigen. We found that 4-week-old BMMC, used as the starting population of the present study, exhibited immature morphologic features, did not present peroxidase activity when cytochemically processed, and released minute amounts of PGD2 in response to IgE-dependent stimulation. When such BMMC were exposed to DM during 24 hours, they showed aldehyde-inhibited peroxidase activity in the perinuclear envelope and a few endoplasmic reticulum segments. As compared with untreated cells, 24-hour DM-exposed BMMC released higher amounts of PGD2 upon immunologic stimulation. After an additional 14-day period of DM exposure, an intense peroxidase activity was detected in the perinuclear envelope and the endoplasmic reticulum of BMMC, which, under immunologic stimulation, released as much as 42.4 +/- 14.7 ng of PGD2/1 x 10(6) cells. Aminotriazole (20 and 50 mM) extinguished both peroxidase activity and PGD2 release from BMMC whereas indomethacin (1 microM) suppressed PGD2 production, but did not alter endogenous peroxidase activity. Previous cell fixation with glutaraldehyde totally inhibited endogenous peroxidase reaction in DM-exposed BMMC. Moreover, 14-day DM-exposed BMMC exhibited morphologic characteristics of mature mast cells and possessed alcian blue+/safranin+ granules. Therefore, the present data suggest that appearance of peroxidase activity in the nuclear envelope and the endoplasmic reticulum of DM-exposed BMMC is associated with the ability of the cells to synthetize PGD2 and appears as a cytochemical marker of the in vitro maturation of mouse bone marrow-derived mast cells.

Aldehydes↗
PubMed1987

Acquisition of peroxidase activity by rat alveolar macrophages during pulmonary inflammation.

The authors investigated the ability of rat alveolar macrophages to acquire peroxidase activity in the course of pulmonary inflammation. Granulomatous pulmonary inflammation was induced in bacille Calmette-Guérin (BCG)-immunized rats by intravenous injection of BCG in mineral oil. In contrast to normal alveolar macrophages, which are peroxidase-negative, alveolar macrophages lavaged from the BCG-treated rats showed significant peroxidase activity in large cytoplasmic inclusions compatible with internalized exogenous material. Alveolar macrophage uptake of intact peroxidase-positive neutrophils was also observed. Maximal numbers of peroxidase-positive alveolar macrophages were observed after the initial influx of neutrophils into the lungs, and peroxidase activity could be demonstrated in cell-free lavage fluid during the acute phase of lung injury. Normal alveolar macrophages acquired peroxidase activity after incubation with peritoneal exudate neutrophils, with purified soluble human myeloperoxidase, and with opsonized erythrocytes. It is concluded that alveolar macrophages acquire peroxidase activity from multiple sources during pulmonary inflammation. Internalization of peroxidase by the alveolar macrophage may serve to clear a potentially toxic enzyme(s) from the alveolar space and contribute to the resolution of pulmonary inflammation.

Animals↗
PubMed1989

Abnormal peroxidase-positive granules in "specific granule" deficiency.

"Specific granule" deficiency (SGD) has been previously associated with lactoferrin deficiency. The antimicrobial peptides termed defensins, comprising 30% of normal primary granule proteins, have also been shown to be markedly deficient in SGD. The present study was undertaken to correlate these findings with ultrastructural morphometric analysis and peroxidase cytochemistry. Peroxidase-positive, rim-stained, large, defensin-rich dense granules, previously described as a subpopulation of azurophil or primary granules in normal neutrophils, were markedly decreased in a patient with SGD. Morphometric studies of peroxidase-positive granules indicated an average peroxidase-positive granule area (all profiles) in the patient of 0.019 +/- 0.017 micron 2 (mean +/- SD, n = 941) compared to control values from normal neutrophils of two volunteers of 0.049 +/- 0.033 micron 2 (n = 896) and 0.050 +/- 0.039 micron 2 (n = 873) (P less than 0.001 between patient and control samples). Granule histograms showed a single peak of small peroxidase-positive granules, whereas control samples contained more prominent subpopulations of larger peroxidase-positive granules. The total number of peroxidase-positive granules per 100 micron 2 of cytoplasm in the patient was 255 +/- 124 (mean +/- SD, n = 15 cell profiles), which was similar to control values of 266 +/- 63 and 212 +/- 109. Thus, the defensin deficiency in SGD is associated with a decrease in size rather than number of peroxidase-positive granules; suggesting that defensins contribute to normal peroxidase-positive granule size and that SGD is a more global granule deficiency than originally thought.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Proteins↗
PubMed1994

Peroxidase activity in murine and human hematopoietic progenitor cells: potential relevance to benzene-induced toxicity.

Peroxidases may be important in the mechanism of toxicity of a number of compounds including benzene, a chemical that has been associated with bone marrow toxicity and leukemia after chronic exposure. The major peroxidase in bone marrow is myeloperoxidase (MPO), which has been previously thought to be expressed at the promyelocytic stage of differentiation. Hematopoietic progenitor cells are important potential cellular targets of bone marrow toxins and leukemogens. We therefore examined peroxidase activity in both murine and human progenitor cells. Murine progenitor populations were purified as lineage-negative cells (> 99% enriched) and human progenitor populations were purified as CD34+ cells (> 95% enriched). Using conventional biochemical assays for peroxidase activity, murine and human progenitor cells were found to have 30% and 11% of the peroxidase activity of murine and human unpurified marrow, respectively. Peroxidase activity was confirmed in purified murine and human progenitor populations by flow cytometry using a 2,7-dichlorofluorescein assay, adapted to measure peroxidase activity. In addition, two-color flow cytometry of murine whole marrow using phycoerythrin-conjugated antibodies to lineage markers confirmed the peroxidase activity of the murine progenitor cell population. A reverse transcription-polymerase chain reaction assay was developed for MPO mRNA, which was detected in murine progenitor cells. These data show that MPO mRNA is expressed in murine progenitor cells and that both murine and human progenitor cells have marked peroxidase activity. These data may have relevance for studies of hematopoietic cell differentiation and for the examination of mechanisms underlying cell-specific toxicity in bone marrow.

Animals↗
PubMed1993

Horseradish peroxidase-catalyzed two-electron oxidations. Oxidation of iodide, thioanisoles, and phenols at distinct sites.

The atypical two-electron oxidation of thioanisole and its p-methyl, p-methoxy, and p-nitro analogues by horseradish peroxidase, contrary to earlier reports, stereoselectively produces the (S) sulfoxides in 60-70% enantiomeric excess. Horseradish peroxidase reconstituted with delta-meso-ethylheme has little peroxidase (guaiacol oxidizing) activity, as previously reported, but exhibits increased sulfoxidation activity. Difference spectroscopy shows that guaiacol binds to delta-meso-ethylheme-reconstituted horseradish peroxidase even though it is essentially not oxidized. In contrast, horseradish peroxidase reconstituted with delta-meso-methylheme is active in both reactions. Studies with H(2)18O2 show that the oxygen in the sulfoxide produced by delta-meso-ethylheme-reconstituted horseradish peroxidase derives, as it does in the reaction catalyzed by the native enzyme, primarily from the peroxide. Preincubation of horseradish peroxidase with phenylhydrazine, which modifies the protein, suppresses peroxidase activity but does not inhibit thioanisole sulfoxidation. On the other hand, the oxidation of iodide is blocked by reconstitution of horseradish peroxidase with delta-meso-ethylheme or preincubation with phenylhydrazine. Noncompetitive kinetics are observed for the inhibition of guaiacol and iodide oxidation by thioanisole and of guaiacol oxidation by iodide. The kinetic data and the differential inhibitory effects of delta-meso-ethylheme reconstitution and phenylhydrazine preincubation indicate that thioanisole and iodide, both of which undergo net two-electron oxidations, are oxidized at sites distinct from each other and from that involved in the oxidation of guaiacol. Spectroscopic substrate binding studies provide support for distinct thioanisole, guaiacol, and iodide-binding sites. An active site model is proposed to rationalize the results.

Anisoles↗
PubMed1995

Peroxidase activity and glutathione content in the human first-trimester placenta and decidua.

OBJECTIVE: Recently, a novel pathway of xenobiotic oxidation by peroxidase in the placenta at term was described. Herein, we aim to determine the potential of the first-trimester placenta and decidua to activate carcinogens and mutagens by peroxidase and to scavenge free radicals by glutathione. METHODS: Placental and decidual peroxidase activity was measured using a sensitive, quantitative colorimetric kinetic assay, with O-phenylenediamine dihydrochloride (OPD) as substrate and H2O2 as co-substrate. Glutathione levels were measured using a colorimetric assay. RESULTS: Peroxidase activity in cytosolic and CaCl2-extracted (membrane-bound) fractions was inhibited by a specific inhibitor, NaN3. The membrane-bound peroxidase activity was maximal at 12 weeks of gestation while cytosolic peroxidase activity did not change. Placental glutathione content remained unchanged during the first trimester. Decidual and placental peroxidase activities were similar; however decidual glutathione content was 15-fold lower, resulting in a higher decidual peroxidase activity/glutathione ratio (p < 0.03). CONCLUSIONS: We report for the first time that peroxidase may be an important pathway for xenobiotic activation at the maternal-embryonal interface. It remains to be established whether the low glutathione content limits the ability of the decidua but not placenta to protect against genomic damage induced through xenobiotic oxidation.

Calcium Chloride↗
PubMed2006

The possible involvement of peroxidase in defense of yellow lupine embryo axes against Fusarium oxysporum.

Peroxidase activity (EC 1.11.1.7) towards phenolic substrates, i.e. pyrogallol, syringaldazine and guaiacol, and ascorbate peroxidase activity (EC 1.11.1.11) were analyzed in embryo axes of Lupinus luteus L. cv. Polo cultured on Heller medium for 96h after inoculation with the necrotrophic fungus Fusarium oxysporum f.sp. Schlecht lupini. Four variants were compared: inoculated embryo axes cultured with 60mM sucrose (+Si) or without it (-Si), and non-inoculated embryo axes cultured with 60mM sucrose (+Sn) or without it (-Sn). Between 0 and 96h of culture, peroxidase activity towards the phenolic substrates increased in all variants except -Si, where a decrease was noted in peroxidase activity towards syringaldazine and guaiacol, but not towards pyrogallol. In +Si tissues, a considerable increase in enzyme activity towards these substrates was recorded starting from 72h of culture. Lignin content of +Si tissues increased already at the first stage of infection, i.e. 24h after inoculation. Additionally, in +Sn tissues, high ascorbate peroxidase activity was observed during the culture. Its activity increased in +Si tissues, beginning at 72h after inoculation. However, this was lower than in +Sn tissues. At 72h after inoculation, a considerably stronger development of the infection was observed in -Si than in +Si tissues during our earlier research [Morkunas, I. et al., 2005. Sucrose-stimulated accumulation of isoflavonoids as a defense response of lupine to Fusarium oxysporum. Plant Physiol Biochem 2005; 43: 363-73]. Both peroxidases assayed towards phenolic substrates and ascorbate peroxidase was less active in -Si tissues than in -Sn tissues. Hydrogen peroxide concentration was much higher in -Si than in +Si tissues. These results indicate that peroxidases may be some of the elements of the defense system that are stimulated by sucrose in yellow lupine embryo axes in response to infection caused by F. oxysporum.

Ascorbate Peroxidases↗
PubMed2004

Defining substrate specificity and catalytic mechanism in ascorbate peroxidase.

Haem peroxidases catalyse the H2O2-dependent oxidation of a variety of, usually organic, substrates. Mechanistically, these enzymes are very well characterized: they share a common catalytic cycle that involves formation of a two-electron oxidized intermediate (Compound I) followed by reduction of Compound I by substrate. The substrate specificity is more diverse, however. Most peroxidases oxidize small organic substrates, but there are prominent exceptions to this and the structural features that control substrate specificity remain poorly defined. APX (ascorbate peroxidase) catalyses the H2O2-dependent oxidation of L-ascorbate and has properties that place it at the interface between the class I (e.g. cytochrome c peroxidase) and classical class III (e.g. horseradish peroxidase) peroxidase enzymes. We present a unified analysis of the catalytic and substrate-binding properties of APX, including the crystal structure of the APX-ascorbate complex. Our results provide new rationalization of the unusual functional features of the related cytochrome c peroxidase enzyme, which has been a benchmark for peroxidase-mediated catalysis for more than 20 years.

Ascorbate Peroxidases↗
PubMed1987

Macromolecular binding of the thyroid carcinogen 3-amino-1,2,4-triazole (amitrole) catalyzed by prostaglandin H synthase, lactoperoxidase and thyroid peroxidase.

3-Amino-1,2,4-triazole, a thyroid carcinogen and goitrogen, is negative in a wide variety of short-term mutagenicity assays. However, amitrole induces gene mutations and morphological transformation in Syrian hamster embryo fibroblasts, cells known to carry out the prostaglandin H synthase (PHS)-mediated peroxidative metabolism of other carcinogens. Therefore, we have investigated the peroxidase-mediated binding of [14C]amitrole to macromolecules in vitro. We report here the PHS- and lactoperoxidase-catalyzed binding of [14C]amitrole to protein and tRNA, as well as protein binding by rat and hog thyroid peroxidase. PHS was an order of magnitude more active than lactoperoxidase and two orders of magnitude more active than thyroid peroxidase. The low levels of binding observed with thyroid peroxidase could be explained by the rapid and potent inhibition of this enzyme by amitrole. Although the thyroid peroxidase-mediated binding of amitrole was quite low, it was not inhibitable by compounds that would be expected to be competing substrates in vivo (i.e. I-, monoiodotyrosine, diiodotyrosine). Neither catalase nor horseradish peroxidase catalyzed binding of [14C]amitrole. It was also observed that an interaction between amitrole and protein and/or nucleic acid resulted in the slow generation of hydrogen peroxide, which then served as a substrate to drive peroxidase-mediated binding of [14C]amitrole. These data suggest that PHS may be responsible for conversion of amitrole to a mutagenic intermediate in Syrian hamster embryo cells. Furthermore, the generation of reactive metabolites of amitrole by thyroid peroxidase and/or PHS may contribute to the complete carcinogenicity of this compound by adding a mutagenic response to its potent hormonal effects.

Amitrole↗
PubMed1999

In vivo role of catalase-peroxidase in synechocystis sp. strain PCC 6803.

The katG gene coding for the only catalase-peroxidase in the cyanobacterium Synechocystis sp. strain PCC 6803 was deleted in this organism. Although the rate of H2O2 decomposition was about 30 times lower in the DeltakatG mutant than in the wild type, the strain had a normal phenotype and its doubling time as well as its resistance to H2O2 and methyl viologen were indistinguishable from those of the wild type. The residual H2O2-scavenging capacity was more than sufficient to deal with the rate of H2O2 production by the cell, estimated to be less than 1% of the maximum rate of photosynthetic electron transport in vivo. We propose that catalase-peroxidase has a protective role against environmental H2O2 generated by algae or bacteria in the ecosystem (for example, in mats). This protective role is most apparent at a high cell density of the cyanobacterium. The residual H2O2-scavenging activity in the DeltakatG mutant was a light-dependent peroxidase activity. However, neither glutathione peroxidase nor ascorbate peroxidase accounted for a significant part of this H2O2-scavenging activity. When a small thiol such as dithiothreitol was added to the medium, the rate of H2O2 decomposition in the DeltakatG mutant increased more than 10-fold, indicating that a thiol-specific peroxidase, for which thioredoxin may be the physiological electron donor, is present. Oxidized thioredoxin is likely to be reduced again by photosynthetic electron transport. Therefore, under laboratory conditions, there are only two enzymatic mechanisms for H2O2 decomposition present in Synechocystis sp. strain PCC 6803. One is catalyzed by a catalase-peroxidase, and the other is catalyzed by thiol-specific peroxidase.

Ascorbate Peroxidases↗
PubMed1994

Effects of manganese deficiency on soluble apoplastic peroxidase activities and lignin content in needles of Norway spruce (Picea abies).

Apoplastic peroxidase activities were investigated in manganese-deficient and manganese-sufficient needles of field-grown Norway spruce trees (Picea abies L.). In Mn-sufficient needles, two sets of peroxidases, one with an alkaline pI >/= 9 and another with an acidic pI </= 3, were identified using guaiacol or coniferylalcohol as substrates for activity staining after isoelectric focusing in a pH gradient from 3 to 9. The acidic peroxidases were capable of Mn-dependent NADH oxidation and H(2)O(2) formation. Syringaldazine peroxidase activity was not found in apoplastic extracts, but was present in whole-needle extracts. Manganese deficiency did not affect the activity or the isoelectric focusing pattern (pH 3 to 9) of the apoplastic peroxidases. Soluble peroxidase activities from whole-needle extracts were significantly higher in Mn-deficient than in Mn-sufficient needles with all substrates tested. Mn-deficient needles contained slightly less cell wall material than Mn-sufficient needles, but the lignin content was similar. Neither apoplastic peroxidase activity nor lignification was affected by Mn deficiency, suggesting that apoplastic peroxidases are regulated independently from symplastic peroxidases.

Journal Article↗
PubMed1993

Soybean Seed Coat Peroxidase (A Comparison of High-Activity and Low-Activity Genotypes).

Peroxidase activity in the seed coats of soybean (Glycine max [L.] Merr.) is controlled by the Ep locus. We compared peroxidase activity in cell-free extracts from seed coat, root, and leaf tissues of three EpEp cultivars (Harosoy 63, Harovinton, and Coles) to three epep cultivars (Steele, Marathon, and Raiden). Extracts from the seed coats of EpEp cultivars were 100-fold higher in specific activity than those from epep cultivars, but there was no difference in specific activity in crude root or leaf extracts. Isoelectric focusing of root tissue extracts and staining for peroxidase activity showed that EpEp cultivars had a root peroxidase of identical isoelectric point to the seed coat peroxidase, whereas roots of the epep types were lacking that peroxidase, indicating that the Ep locus may also affect expression in the root. In seed coat extracts, peroxidase was the most abundant soluble protein in EpEp cultivars, whereas this enzyme was present only in trace amounts in epep genotypes, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Histochemical localization of peroxidase activity in seed coats of EpEp cultivars shows that the enzyme occurs predominately in the cytoplasm of hourglass cells of the subepidermis. No obvious difference in the gross or microscopic structure of the seed coat was observed to be associated with the Ep locus. These results suggest that soybean seed coat peroxidase may be involved in processes other than seed coat biosynthesis.

Journal Article↗
PubMed1975

The reaction of coumarins with horseradish peroxidase.

The peroxidase catalyzed oxidation of indole-3-acetate is inhibited by naturally occurring coumarins such as scopoletin. This inhibition is due to the preferential reactivity of the coumarins with the peroxidase compounds I, II, and III. In view of the possible growth regulatory role of coumarins in plants, the mechanism of oxidation of scopoletin by horse-radish peroxidase has been investigated.Peroxidase catalyzed coumarin oxidation requires either an electron donor and molecular oxygen or hydrogen peroxide. If peroxide is present, the reaction is mediated by peroxidase compound II which reacts rapidly and stoichiometrically with scopoletin. Different oxidation products are formed, depending on whether IAA or hydrogen peroxide promotes the reaction. A scopoletin-free radical intermediate has been isolated from the peroxide reaction mixture but was not detected in the peroxide-free system.When indole-3-acetate is the electron donor, reduced peroxidase combines with molecular oxygen to give peroxidase compound III. Added scopoletin is cooxidized with indole-3-acetate. Compared to the scopoletin peroxidation, this reaction is slower and yields fewer coumarin oxidation products. The differences observed between the two scopoletin oxidation pathways reflect: (a) the competition between indole-3-acetate and scopoletin for peroxidase compounds; (b) the lower reactivity of scopoletin with peroxidase compound III compared with peroxidase compound II. The peroxide-promoted reaction is eliminated by catalase, while the indole-3-acetate initiated oxidation is not affected by excess quantities of either catalase or superoxidase dismutase.

Journal Article↗
PubMed1987

The Effect of Pseudomonas putida Colonization on Root Surface Peroxidase.

Increased activities of peroxidase and indole 3-acetic acid (IAA) oxidase were detected on root surfaces of bean (Phaseolus vulgaris) seedlings colonized with a soil saprophytic bacterium, Pseudomonas putida. IAA oxidase activity increased over 250-fold and peroxidase 8-fold. Enhancement was greater for 6-day-old than for 4- or 8-day-old inoculated plants No IAA oxidase or peroxidase activities were associated with the bacterial cells. Native polyacrylamide gel electrophoresis demonstrated that washes of P. putida-inoculated roots contained two zones of peroxidase activity. Only the more anodic bands were detected in washes from noninoculated roots. Ion exchange and molecular sizing gel chromatography of washes from P. putida-colonized roots separated two fractions of peroxidase activity. One fraction corresponded to the anodic bands detected in washes of P. putida inoculated and in noninoculated roots. A second fraction corresponded to the less anodic zone of peroxidase, which was characteristic of P. putida-inoculated plants. This peroxidase had a higher IAA oxidase to peroxidase ratio than the more anodic, common enzyme. The changes in root surface peroxidases caused by colonization by a saprophytic bacterium are discussed with reference to plant-pathogen interactions.

Journal Article↗