Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PEROXIDASES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24Linked to original sources
PubMed1985

Methyl ethyl ketone peroxide damage to cytochrome P-450 peroxidase activities.

Some new aspects of damage to cytochrome P-450 peroxidase activities by a toxic peroxide were investigated. Methyl ethyl ketone peroxide (MEKP) damage to cytochrome P-450 and inhibition of cytochrome P-450-mediated peroxidase activities were studied. In vivo, hepatic microsomal NADH- and NADPH-peroxidase activities were induced in rats by phenobarbital and 3-methylcholanthrene. Phenobarbital treatment induced more NADH- and NADPH-peroxidase activity than did 3-methylcholanthrene treatment. In vitro, microsomal cytochrome P-450 from rat liver was more sensitive to damage by MEKP than was this protein from rat kidney. Destruction of cytochrome P-450 hemoprotein and inhibition of its associated peroxidase activities by MEKP increased as a function of time of exposure to the peroxide. The addition of MEKP to microsomes resulted in a progressive increase in spectral absorbance at 433 nm. MEKP was an irreversible inhibitor of NADH- and NADPH-peroxidase, and NADH-peroxidase was more sensitive to damage than was NADPH-peroxidase. At 0 time and low concentration, MEKP was immediately bound to microsomal cytochrome P-450 and it exhibited competitive inhibition of NADH- and NADPH-peroxidase. At high concentration, MEKP was a mixed inhibitor of NADH- and NADPH-peroxidase. This study also showed that MEKP is a substrate for microsomal P-450 peroxidase activities and suggests that these peroxidase activities may play an important role in metabolism of toxic lipophilic organic peroxides that enter the endoplasmic reticulum.

Animals↗
PubMed1984

Endogenous peroxidase activity in mononuclear phagocytes.

The diaminobenzidine (DAB) technique has been used to visualize the subcellular localization of peroxidatic enzymes in mononuclear phagocytes. The latter cells are part of the mononuclear phagocyte system (MPS), which includes the monocytes in the bone marrow and blood, their precursors in the bone marrow, and the resident macrophages in the tissues. The DAB cytochemistry has revealed distinct subcellular distribution patterns of peroxidase in the mononuclear phagocytes. Thus the technique facilitates the identification of the various phagocyte types: Promonocytes contain peroxidase reaction in the nuclear envelope, endoplasmic reticulum, Golgi apparatus, and cytoplasmic granules. Monocytes exhibit the reaction product only in cytoplasmic granules. Most resident macrophages show the activity only in the nuclear envelope and endoplasmic reticulum. Furthermore, new phagocyte types have been detected based on the peroxidase cytochemistry. Intermediate cells between monocytes and resident macrophages contain reaction product in the nuclear envelope, endoplasmic reticulum and cytoplasmic granules. The resident macrophages can be divided into two subtypes. Most of them exhibit the pattern noted above. Some, however, are totally devoid of peroxidase reaction. Most studies on peroxidase cytochemistry of monocytes and macrophages agree that the peroxidase patterns reflect differentiation or maturation stages of one cell line. Some authors, however, still interpret the patterns as invariable characteristics of separate cell lines. As to the function of the peroxidase in phagocytes, the cytochemical findings imply that two different peroxidatic enzymes exist in the latter cells: one peroxidase is synthesized in the endoplasmic reticulum of promonocytes and transported to granules via the Golgi apparatus. The synthesis ceases when the promonocyte matures to the monocyte. Upon phagocytosis the peroxidase is discharged into the phagosomes. Biochemical and functional studies have indicated that this peroxidase (myeloperoxidase) is part of a microbicidal system operating in host defence mechanisms. The other enzyme with peroxidatic activity is confined to the nuclear envelope and endoplasmic reticulum of resident macrophages in-situ and of monocytes at early stages in culture. As suggested by the subcellular distribution, the inhibition by peroxidase blockers, and the localization during phagocytosis studies, the latter peroxidase is functionally different from the myeloperoxidase.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

Retrograde and transganglionic transport of horseradish peroxidase-conjugated cholera toxin B subunit, wheatgerm agglutinin and isolectin B4 from Griffonia simplicifolia I in primary afferent neurons innervating the rat urinary bladder.

In the present study, we investigated and compared the ability of the cholera toxin B subunit, wheat germ agglutinin and isolectin B4 from Griffonia simplicifolia I conjugated to horseradish peroxidase, to retrogradely and transganglionically label visceral primary afferents after unilateral injections into the rat urinary bladder wall. Horseradish peroxidase histochemical or lectin-immunofluorescence histochemical labelling of bladder afferents was seen in the L6-S1 spinal cord segments and in the T13-L2 and L6-S1 dorsal root ganglia. In the lumbosacral spinal cord, the most intense and extensive labelling of bladder afferents was seen when cholera toxin B subunit-horseradish peroxidase was injected. Cholera toxin B subunit-horseradish peroxidase-labelled fibres were found in Lissauer's tract, its lateral and medial collateral projections, and laminae I and IV-VI of the spinal gray matter. Labelled fibres were numerous in the lateral collateral projection and extended into the spinal parasympathetic nucleus. Labelling from both the lateral and medial projections extended into the dorsal grey commissural region. Wheat germ agglutinin-horseradish peroxidase labelling produced a similar pattern but was not as dense and extensive as that of cholera toxin B subunit-horseradish peroxidase. The isolectin B4 from Griffonia simplicifolia I-horseradish peroxidase-labelled fibres, on the other hand, were fewer and only observed in the lateral collateral projection and occasionally in lamina I. Cell profile counts showed that a larger number of dorsal root ganglion cells were labelled with cholera toxin B subunit-horseradish peroxidase than with wheat germ agglutinin- or isolectin B4-horseradish peroxidase. In the L6-S1 dorsal root ganglia, the majority (81%) of the cholera toxin B subunit-, and almost all of the wheat germ agglutinin- and isolectin B4-immunoreactive cells were RT97-negative (an anti-neurofilament antibody that labels dorsal root ganglion neurons with myelinated fibres). Double labelling with other neuronal markers showed that 71%, 43% and 36% of the cholera toxin B subunit-immunoreactive cells were calcitonin gene-related peptide-, isolectin B4-binding- and substance P-positive, respectively. A few cholera toxin B subunit cells showed galanin-immunoreactivity, but none were somatostatin-, vasoactive intestinal polypeptide-, or neuropeptide Y-immunoreactive or contained fluoride-resistant acid phosphatase. The results show that cholera toxin B subunit-horseradish peroxidase is a more effective retrograde and transganglionic tracer for pelvic primary afferents from the urinary bladder than wheat germ agglutinin-horseradish peroxidase and isolectin B4-horseradish peroxidase, but in contrast to somatic nerves, it is transported mainly by unmyelinated fibres in the visceral afferents.

Animals↗
PubMed1996

An engineered cation site in cytochrome c peroxidase alters the reactivity of the redox active tryptophan.

The crystal structures of cytochrome c peroxidase and ascorbate peroxidase are very similar, including the active site architecture. Both peroxidases have a tryptophan residue, designated the proximal Trp, located directly adjacent to the proximal histidine heme ligand. During the catalytic cycle, the proximal Trp in cytochrome c peroxidase is oxidized to a cation radical. However, in ascorbate peroxidase, the porphyrin is oxidized, not the proximal Trp, despite the close similarity between the two peroxidase active site structures. A cation located approximately 8 A from the proximal Trp in ascorbate peroxidase but absent in cytochrome c peroxidase is thought to be one reason why ascorbate peroxidase does not form a Trp radical. Site-directed mutagenesis has been used to introduce the ascorbate peroxidase cation binding site into cytochrome c peroxidase. Crystal structures show that mutants now bind a cation. Electron paramagnetic resonance spectroscopy shows that the cation-containing mutants of cytochrome c peroxidase no longer form a stable Trp radical. The activity of the cation mutants using ferrocytochrome c as a substrate is < 1% of wild type levels, while the activity toward a small molecule substrate, guaiacol, increases. These results demonstrate that long range electrostatic effects can control the reactivity of a redox active amino acid side chain and that oxidation/reduction of the proximal Trp is important in the oxidation of ferrocytochrome c.

Animals↗
PubMed2004

Activity and isoforms of peroxidases, lignin and anatomy, during adventitious rooting in cuttings of Ebenus cretica L.

Adventitious rooting of Ebenus cretica cuttings was studied in order to examine a) the rooting ability of different genotypes in relation to electrophoretic patterns of peroxidases. b) the activity and electrophoretic patterns of soluble and wall ionically bound peroxidases, the lignin content and anatomical changes in the control and IBA treated cuttings of and genotypes in the course of adventitious root formation. In addition, a fraction of soluble cationic peroxidases was separated by gel filtration chromatography from the total soluble peroxidases of a genotype. No rooting occurred in cuttings without IBA-treatment. In both genotypes, electrophoretic patterns of soluble anionic peroxidases revealed two common peroxidase isoforms, while a fast-migrating anionic peroxidase isoform (A3) appeared only in genotypes. Both genotypes showed similar patterns of soluble, as well as wall ionically bound cationic peroxidase isoforms. The number of isoforms was unchanged during the rooting process (induction, initiation and expression phase) but an increase in peroxidase activity (initiation phase) followed by decrease has been found in IBA-treated cuttings. During initiation phase the lignin content was almost similar to that on day 0 in genotype while it was reduced at by about 50% in genotype at the respective time. Microscopic observations revealed anatomical differences between genotypes. According to this study, the and genotypes display differences in anatomy, lignin content, activity of soluble peroxidases and the electrophoretic patterns of soluble anionic peroxidase isoforms. The A3-anionic peroxidase isoform could be used as biochemical marker to distinguish and genotypes of E. cretica and seems to be correlated to lignin synthesis in rooting process.

Ebenaceae↗
PubMed2003

Three differentially expressed basic peroxidases from wound-lignifying Asparagus officinalis.

The activity of ionically bound peroxidases from an asparagus spear increased from 5-24 h post-harvest. Isoelectric focusing showed that the post-harvest increase of the total peroxidase activity was due to the increase of several distinct isoperoxidases. Concomitantly, a decrease in the activity of two anionic peroxidases was observed. Peroxidases with pI 5.9, 6.4 and 9.2 were detected only at 24 h post-harvest, whereas four peroxidases, with pI 8.7, 8.1, 7.4, and 6.7, detected throughout the time-course, increased in their activity. Histochemical staining demonstrated that lignin and peroxidase activity were located in the vascular bundles throughout the period of measurement. Lignin was detected in the cell walls of the protoxylem in the vascular bundles of the asparagus stem. A cDNA library of mRNA isolated from asparagus spears 24 h post-harvest was screened for peroxidases using homologous and heterologous probes. Three clones were isolated and the corresponding mature asparagus peroxidases displayed 70%, 76% and 81% amino acid sequence identity to each other. These new asparagus peroxidases are typical class III plant peroxidases in terms of conserved regions with a calculated pI >9.2, which is consistent with most basic peroxidases. One of the genes was shown to be a constitutively expressed single-copy gene, whereas the others showed an increased expression at post-harvest. The highest similarity in the amino acid sequence (71-77%) was found in peroxidases from roots of winter grown turnip TP7, to Arabidopsis AtP49, to an EST sequence from cotton fibres and to TMV-infected tobacco.

Amino Acid Sequence↗
PubMed2004

Phylogenetic relationships in class I of the superfamily of bacterial, fungal, and plant peroxidases.

Molecular phylogeny among catalase-peroxidases, cytochrome c peroxidases, and ascorbate peroxidases was analysed. Sixty representative sequences covering all known subgroups of class I of the superfamily of bacterial, fungal, and plant heme peroxidases were selected. Each sequence analysed contained the typical peroxidase motifs evolved to bind effectively the prosthetic heme group, enabling peroxidatic activity. The N-terminal and C-terminal domains of catalase-peroxidases matching the ancestral tandem gene duplication event were treated separately in the phylogenetic analysis to reveal their specific evolutionary history. The inferred unrooted phylogenetic tree obtained by three different methods revealed the existence of four clearly separated clades (C-terminal and N-terminal domains of catalase-peroxidases, ascorbate peroxidases, and cytochrome c peroxidases) which were segregated early in the evolution of this superfamily. From the results, it is obvious that the duplication event in the gene for catalase-peroxidase occurred in the later phase of evolution, in which the individual specificities of the peroxidase families distinguished were already formed. Evidence is presented that class I of the heme peroxidase superfamily is spread among prokaryotes and eukaryotes, obeying the birth-and-death process of multigene family evolution.

Amino Acid Sequence↗
PubMed1978

Cofactor role of iodide in peroxidase antimicrobial action against Escherichia coli.

The mechanism of antimicrobial activity of the peroxidase-hydrogen peroxide (H(2)O(2))-iodide (I(-)) system was investigated. Inhibition of respiration and loss of viability of Escherichia coli were used as measures of antimicrobial activity. Because the bacteria destroyed H(2)O(2), peroxidase antimicrobial action depended on the competition for H(2)O(2) between the bacteria and the peroxidase. Utilization of H(2)O(2) by the peroxidase was favored by (i) increasing either the peroxidase or the I(-) concentration, so as to increase the rate of oxidation of I(-), (ii) lowering the temperature to lower the rate of destruction of H(2)O(2) by the bacteria, and (iii) adding H(2)O(2) in small increments so as to avoid a large excess of H(2)O(2) relative to I(-). When utilization of H(2)O(2) by the peroxidase system was favored, the peroxidase system and iodine (I(2)) were equivalent. That is, antimicrobial action per mole of H(2)O(2) equaled that per mole of I(2). Also, identical antimicrobial action was obtained either by incubating the bacteria directly with the peroxidase system or by preincubating the peroxidase system so as to form I(2) and then adding the bacteria. On the other hand, peroxidase antimicrobial action could be obtained at low I(-) concentrations. These I(-) concentrations were lower than the concentration of I(2) that was required for antimicrobial action. It is proposed that peroxidase-catalyzed oxidation of I(-) yields I(2), which reacts with bacterial components to yield the oxidized components and I(-). The I(-) that is released can be reoxidized and participate again in the oxidation of bacterial components. In this way, I(-) acts as a cofactor in the peroxidase-catalyzed oxidation of bacterial components.

Coenzymes↗
PubMed1989

Thyroid peroxidase: rat cDNA sequence, chromosomal localization in mouse, and regulation of gene expression by comparison to thyroglobulin in rat FRTL-5 cells.

A rat thyroid peroxidase cDNA has been isolated from a FRTL-5 thyroid cell library and sequenced. The cDNA is 2776 base pairs long with an open reading frame of 770 amino acids. By comparison to full-length human thyroid peroxidase cDNA and based on its identification of a 3.2 kilobase mRNA in rat thyroid FRTL-5 cell Northern blots, the rat peroxidase cDNA appears to lack 400-500 base pairs at the 5'-end of the mRNA. It exhibits only a 74% nucleotide and 77% amino acid sequence similarity to human thyroid peroxidase cDNA within the total aligned sequences, although the predicted active site regions are highly conserved (greater than 90-100%). The cDNA has been used to map the thyroid peroxidase gene in mice to chromosome 12 and to compare thyroid peroxidase and thyroglobulin gene expression in FRTL-5 rat thyroid cells. Despite the fact TSH action in both cases is duplicated, and presumably mediated, by cAMP, TSH-induced increases in thyroid peroxidase and thyroglobulin mRNA levels differ. Differences exist with respect to hormone concentration and time. The ability of TSH to increase thyroglobulin, but not thyroid peroxidase mRNA levels, requires insulin, 5% serum, or insulin-like growth factor-I. Insulin or insulin-like growth factor-I alone can increase thyroglobulin mRNA levels as well as or better than TSH but have only a small effect on thyroid peroxidase mRNA levels by comparison to TSH. The ability of TSH to increase thyroglobulin gene expression is readily detected in nuclear run-on assays but not the ability of TSH to increase thyroid peroxidase gene expression. Cycloheximide inhibits TSH-increased thyroglobulin but not peroxidase mRNA levels. Finally, methimazole and phorbol 12-myristate 13-acetate show different effects on TSH-induced increases in thyroglobulin and thyroid peroxidase mRNA levels.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1991

Why no simple relationship between thyroid peroxidase activity-inhibiting immunoglobulins and thyroid function in autoimmune thyroid disease?

We have reported that some anti-thyroid peroxidase antibodies inhibit the activity of thyroid peroxidase in vitro. These thyroid peroxidase activity-inhibiting immunoglobulins seem to inhibit thyroid function in some patients, but the relationship between thyroid peroxidase activity-inhibiting immunoglobulins and thyroid function is not simple. We designed this study to explore this lack of a simple relationship. We stained immunoglobulin G deposits by immunofluorescence staining or the peroxidase-antiperoxidase method, and stained endogenous thyroid peroxidase activity by enzyme histochemistry in thyroid sections. When cryostat thyroid sections were incubated with thyroid peroxidase activity-inhibiting immunoglobulins, immunoglobulin G deposits were seen as lines of stain on the apical border and as intracellular staining, and endogenous thyroid peroxidase activity was inhibited. In paraffin-embedded thyroid sections from 5 Hashimoto's patients and 6 Graves' patients, immunoglobulin G deposits were not found on the apical border of the follicular epithelium. In frozen thyroid sections from 22 Graves' patients, no clear deposits of immunoglobulin G on this apical border were seen. In organ-cultured thyroid slices incubated with thyroid peroxidase activity-inhibiting immunoglobulins, endogenous thyroid peroxidase activity was not inhibited. In conclusion, thyroid peroxidase activity-inhibiting immunoglobulins may reach its antigen only with difficulty. This is one of the reasons why no simple relationship is observed between thyroid peroxidase activity-inhibiting immunoglobulins and thyroid function.

Antigens↗
PubMed1995

Crystal structure of recombinant pea cytosolic ascorbate peroxidase.

The crystal structure of recombinant pea cytosolic ascorbate peroxidase has been refined to an R = 0.19 for data between 8.0 and 2.2 A resolution and magnitude of F > or = 2 sigma(magnitude of F). The refined model consists of four ascorbate peroxidase monomers consisting of 249 residues per monomer assembled into two homodimers, with one heme group per monomer. The ascorbate peroxidase model confirms that the pea cytosolic enzyme is a noncovalent homodimer held together by a series of ionic interactions arranged around the 2-fold noncrystallographic dimer axis. As expected from the high level of sequence identity (33%), the overall fold of the ascorbate peroxidase monomer closely resembles that of cytochrome c peroxidase. The average root mean square differences for 137 helical alpha-carbon atoms between the four ascorbate peroxidase monomers and cytochrome c peroxidase and for 249 topologically equivalent alpha-carbon atoms are 0.9 and 1.3 A, respectively. The active site structures are also the same, including the hydrogen-bonding interactions between the proximal His ligand, a buried Asp residue, and a Trp residue, whose indole ring is parallel to and in contact with the proximal His ligand just under the heme ring. This proximal Trp residue is thought to be the site of free radical formation in cytochrome c peroxidase compound I and is also essential for enzyme activity. The corresponding Trp in ascorbate peroxidase, Trp179, occupies exactly the same position. The most interesting, and possibly functionally important, difference between the two peroxidases is the presence of a cation binding site in ascorbate peroxidase located approximately 8 A from the alpha-carbon atom of Trp179.

Ascorbate Peroxidases↗
PubMed1995

Identification of a porphyrin pi cation radical in ascorbate peroxidase compound I.

Electron paramagnetic resonance (EPR) spectroscopy has been used to analyze the ascorbate peroxidase Fe3+ resting state and to compare the reaction product between the enzyme and H2O2, compound I, with that of cytochrome c peroxidase. Because ascorbate peroxidase has a Trp residue in the proximal heme pocket at the same location as the Trp191 compound I free radical in cytochrome c peroxidase [Patterson, W. R., & Poulos, T. L. (1995) Biochemistry 34, 4331-4341], it was anticipated that ascorbate peroxidase compound I might also contain a Trp-centered radical. However, the ascorbate peroxidase compound I EPR spectrum is totally different from that of cytochrome c peroxidase. Immediately after the addition of H2O2, the 7.5 K EPR spectrum of ascorbate peroxidase compound I exhibits an axial resonance extending from g perpendicular = 3.27 to g parallel approximately 2 that disappears within 30 s, presumably due to endogenous reduction of compound I. In contrast, cytochrome c peroxidase compound I exhibits a long-lived g approximately 2 signal associated with the Trp191 cation free-radical [Houseman, A. L. P., et al. (1993) Biochemistry 32, 4430-4443]. Recently, the 2 K EPR spectrum of a catalase compound I was found to exhibit a broad signal extending from g perpendicular = 3.45 to g parallel approximately 2 and was interpreted as a porphyrin pi cation radical [Benecky, M. J., et al. (1993) Biochemistry 32, 11929-11933]. On the basis of these comparisons, we conclude that ascorbate peroxidase forms an unstable compound I porphyrin pi cation radical, even though it has a Trp residue positioned precisely where the Trp191 radical is located in cytochrome c peroxidase.

Ascorbate Peroxidases↗
PubMed2004

Root growth inhibition by aluminum is probably caused by cell death due to peroxidase-mediated hydrogen peroxide production.

The effect of aluminum on hydrogen peroxide production and peroxidase-catalyzed NADH oxidation was studied in barley roots germinated and grown between two layers of moistened filter paper. Guaiacol peroxidase activity significantly increased after 48 h and was approximately two times higher after 72 h in Al-treated roots. The oxidation of NADH was also significantly increased and, like guaiacol peroxidase activity, it was two times higher in A1-treated roots than in controls. Elevated H2O2 production was observed both 48 and 72 h after the onset of imbibition in the presence of A1. Separation on a cation exchange column allowed the detection of two peaks with NADH peroxidase and H2O2 production activity. However, a difference between control and Al-treated plants was found only in one fraction, in which four times higher guaiacol peroxidase activity and five times higher NADH peroxidase activity were expressed and about three times more H2O2 was produced. One anionic peroxidase and three cationic peroxidases were detected in this fraction by native polyacrylamide gel electrophoresis. The anionic peroxidase was activated in the Al-treated root tips and also oxidized NADH but was detectable only after a long incubation time. Two of the cationic peroxidases were capable of oxidizing NADH and producing a significant amount of H2O2, but only one of these was activated by A1 stress. The role of these peroxidases during A1 stress in barley root tips is discussed.

Aluminum↗
PubMed1990

Luminol chemiluminescence reaction catalyzed by a microbial peroxidase.

A peroxidase produced by microorganisms belonging to the genera Arthromyces and Coprinus was found to be a potent catalyst for the chemiluminescent oxidation of luminol, the luminescence produced per unit of microbial peroxidase protein being well over 100 times as strong as that produced by horseradish peroxidase. No large difference in Km value for H2O2 in the presence of luminol was found between Arthromyces ramosus peroxidase and horseradish peroxidase (7.0 and 15.5 microM, respectively), but Vmax of the Arthromyces peroxidase was 500 times greater than that of the horseradish peroxidase. It was also found that the Arthromyces peroxidase surpasses, beyond expectation, the horseradish peroxidase in the initial velocity of the chemiluminescence reaction with the stopped-flow method. The Arthromyces peroxidase was used for the glucose and cholesterol assays, which were notably more sensitive than the corresponding assays involving the horseradish peroxidase.

Calibration↗
PubMed1987

Uptake and axonal transport of horseradish peroxidase isoenzymes by different neuronal types.

The uptake and transport of basic and acidic horseradish peroxidase isoenzymes was compared in the neuromuscular, visual and olfactory systems of Xenopus larvae and postmetamorphic frogs. The concentration (w/v) of the two preparations was corrected to compensate for their difference in enzymatic activity (unit/w), which was seven-fold higher in basic horseradish peroxidase. Uptake and transport of horseradish peroxidase isoenzymes could be demonstrated with 7% basic horseradish peroxidase, but not with equal amounts of 49% acidic horseradish peroxidase in all systems investigated: retrograde transport from terminals of retinal ganglion cells, isthmotectal neurons and spinal motoneurons, as well as anterograde transganglionic transport along olfactory neurons. A very weak labelling of the same neuronal pathways by acidic horseradish peroxidase was obtained only after increasing the amount injected by approximately two-fold. Basic horseradish peroxidase isoenzymes were also preferentially taken up and transported retrogradely by broken axons of the optic nerve. When tested, similar results were obtained in both larvae and frogs suggesting that preferential uptake and transport of basic horseradish peroxidase is a general feature of all neurons and of all developmental stages. Electron microscopical analysis of the outer layers of the optic tectum revealed that, in the same experimental conditions producing no retrotrade labelling of optic axons, acidic horseradish peroxidase was rarely found to enter nerve terminals. It appears that interactions between horseradish peroxidase and neuronal membranes occur during uptake and transport and that molecular charge plays an important role, beyond non-specific fluid-phase endocytosis. We suggest that differences between horseradish peroxidase isoenzymes as neuronal tracers reflect a process of adsorptive endocytosis related to general characteristics of neuronal membranes (regardless of age) and not to specific receptor-mediated interactions characteristic of neuronal specificity.

Animals↗
PubMedDate not supplied

[Peroxidase and human thyroid hormone synthesis disorders (author's transl)].

Thyroid peroxidase in involved in several steps of the biosynthesis of thyroid hormone utilizing H2O2: peroxidation of iodide to iodine, iodination of thyroglobulin (Tg) and coupling reaction leading to T4 and T3 formation. The peroxidase enzyme appears to be an heme protein containing a protoporphyrin IX, with binding sites for both iodide and tyrosine. Although the peroxidase is present in numerous cellular structure, iodination activity occurs primarily if not only at all, at the apical cell border. Lack of peroxidase activity or abnormal peroxidase has been described in isolated cases of congenital goiter with organification defect and a positive perchlorate test. However no change in enzymatic activity has been found in patients with Pendred's syndrome as compared to normal tissue. The deficiency of hormone synthesis observed in various benign diffuse thyroid disorders in certainly not due to a lack of peroxidase activity. In treated hyperthyroid patients, a high cellular activity is observed, especially at the apical cell border. In euthyroid patients with diffuse sporadic goiter, an increase of peroxidase activity is also observed. However, the cytochemical localization of the enzyme in goitrous thyroid gland shows that the peroxidase activity is mostly visualized around numerous lipoid structures; being concentrated in this particular site, the enzyme might preferentially oxidize lipids and consequently be less available for hormone synthesis. In euthyroid hot nodule, the peroxidase activity is normal. In cold nodule, a discrepancy between iodide oxidation and protein iodination has been found, suggesting that iodide peroxidation and iodination of tyrosine residues of Tg are two relatively independent processes although thyroid peroxidase catalyses both reactions. In contrast with the benign pathological conditions, the peroxidase activity is lower than normal in thyroid cancerous tissue.

Humans↗
PubMed1999

Addition of veratryl alcohol oxidase activity to manganese peroxidase by site-directed mutagenesis.

Manganese peroxidase and lignin peroxidase are ligninolytic heme-containing enzymes secreted by the white-rot fungus Phanerochaete chrysosporium. Despite structural similarity, these peroxidases oxidize different substrates. Veratryl alcohol is a typical substrate for lignin peroxidase, while manganese peroxidase oxidizes chelated Mn2+. By a single mutation, S168W, we have added veratryl alcohol oxidase activity to recombinant manganese peroxidase expressed in Escherichia coli. The kcat for veratryl alcohol oxidation was 11 s-1, Km for veratryl alcohol approximately 0.49 mM, and Km for hydrogen peroxide approximately 25 microM at pH 2.3. The Km for veratryl alcohol was higher and Km for hydrogen peroxide was lower for this manganese peroxidase mutant compared to two recombinant lignin peroxidase isoenzymes. The mutant retained full manganese peroxidase activity and the kcat was approximately 2.6 x 10(2) s-1 at pH 4.3. Consistent with relative activities with respect to these substrates, Mn2+ strongly inhibited veratryl alcohol oxidation. The single productive mutation in manganese peroxidase suggested that this surface tryptophan residue (W171) in lignin peroxidase is involved in catalysis.

Alcohol Oxidoreductases↗
PubMed1993

Deficient glutathione peroxidase activity in preeclampsia is associated with increased placental production of thromboxane and lipid peroxides.

OBJECTIVE: Thromboxane and lipid peroxide levels are abnormally increased in preeclamptic placentas. The cause of this increase is not known. Peroxides stimulate prostaglandin H2 synthase to increase thromboxane and oxygen radicals, which increase lipid peroxides. Glutathione peroxidase inactivates peroxides, thereby decreasing peroxide stimulation of prostaglandin H synthase. If glutathione peroxidase activity were deficient, then peroxides could increase, leading to increased stimulation of prostaglandin H synthase, resulting in increased production of thromboxane and lipid peroxides. The following study tested this hypothesis. STUDY DESIGN: Placental tissues from 11 normal and 11 preeclamptic women were immediately frozen in liquid nitrogen after delivery. One gram of tissue from each placenta was homogenized for analysis. Placental tissues were also obtained from six normal pregnancies for incubation with a glutathione peroxidase inhibitor, N-ethylmaleimide. Samples were analyzed for glutathione peroxidase activity, lipid peroxides by hydrogen peroxide equivalents, thromboxane by thromboxane B2, and prostacyclin by 6-keto-prostaglandin F1 alpha. RESULTS: Glutathione peroxidase activity was significantly lower in preeclamptic than in normal placentas (9.41 +/- 0.05 vs 13.41 +/- 0.63 units/gm, p < 0.001, mean +/- SE). Lipid peroxides and thromboxane were significantly higher in preeclamptic than in normal placentas (hydrogen peroxide equivalents 4.23 +/- 0.32 vs 2.84 +/- 0.27 mumol/gm, p < 0.01; thromboxane B2 215 +/- 31 vs 138 +/- 15 ng/gm, p < 0.05), whereas prostacyclin was significantly lower (6-keto-prostaglandin F1 alpha 23.3 +/- 2.2 vs 41.6 +/- 6.0 ng/gm, p < 0.01). Inhibition of glutathione peroxidase activity in normal placentas resulted in a dose-response increase in placental production of both lipid peroxides and thromboxane without affecting prostacyclin, so the ratio of thromboxane to prostacyclin increased progressively with inhibition of glutathione peroxidase. CONCLUSIONS: Glutathione peroxidase activity is significantly lower, and lipid peroxides and thromboxane are significantly higher, in preeclamptic placentas compared with normal placentas. Inhibition of glutathione peroxidase activity in normal placentas results in significantly increased production of lipid peroxides and thromboxane and an increase in the thromboxane to prostacyclin ratio. We speculate that in normal placentas, glutathione peroxidase limits prostaglandin H synthase activity by reducing the amount of peroxide present, thus reducing peroxide stimulation of prostaglandin H synthase. In preeclampsia deficient glutathione peroxidase activity results in in increased peroxide levels leading to increased stimulation of prostaglandin H synthase, which results in increased production of lipid peroxides and thromboxane.

Case-Control Studies↗