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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ascorbate peroxidase active component (APAC) was purified and characterized in Synechococcus PCC 9742 (R2) cells. APAC was isolated from freshly harvested cells, by ion exchange chromatography on DEAE cellulose, ultrafiltration through a 3000 dalton cut off filter and high pressure liquid chromatography through a reversed phase C-18 column. APAC was found to be extremely stable to harsh treatments of boiling water for 30 min, acidification to pH 2.0 and proteolytic digestion. A close correlation between activity and iron content of APAC was observed throughout the purification steps. E.S.R. spectrum of APAC showed a resonance line at g = 4.3 in the oxidized from. Peroxide reduction by ascorbate decreased the E.S.R. signal, which reappeared upon reoxidation by H2O2. The affinities of APAC to H2O2 and ascorbate were high (0.38 mM and 0.2 mM, respectively). Amino acid composition analysis of APAC revealed the presence of glutamic acid:glycine:cysteine residues at 2:1:1 ratio.
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PMID:A unique ascorbate peroxidase active component in the cyanobacterium Synechococcus PCC 7942 (R2). 133 15

This study aimed to determine the kinetics of albumin resorption from and the healing of two types of albumin impregnated Vasculour II (Bard Cardiovascular) Dacron grafts (ACG-A and ACG-B) using whole blood preclotted Vasculour II Dacron grafts (without albumin) as controls (PCC). Prostheses measuring 4 mm ID x 50 mm length were implanted in the aortoiliac position in 24 dogs (ACG-A n = 12, ACG-B n = 24, PCC n = 12) and explanted after 1, 2 4, and 6 months. Platelet count, platelet aggregometry to 10(-5) M ADP, prothrombin time (PT), and partial thromboplastin time (PTT) were determined preoperatively and at explantation. Sections of the explanted grafts were assayed for human albumin by immunohistochemical techniques utilizing a rabbit polyclonal mono-specific antibody for human albumin followed by the addition of a biotinylated goat anti-rabbit IgG. Immunoperoxidase staining was then performed using Avidin D horse-radish peroxidase. Histology of the grafts (light microscopy, scanning electron microscopy, and transmission electron microscopy) as well as percent thrombus free surface area (TFSA) by computerized planimetry were also determined. Seven of 48 grafts were occluded (85.4% patency) with no difference among the three groups. Platelet aggregometry was not predictive of graft patency. No change in PT or PTT occurred nor was there any difference among the three groups. Retained albumin was detected in every one-month explant but not beyond that time, with the sensitivity for detecting human albumin in this assay being 20 mg albumin per gram of Dacron. All ACG explants at one month revealed inner capsular fibrin coagula not present in PCC specimens.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Albumin impregnated vascular grafts: albumin resorption and tissue reactions. 138 74

Oxidative stress responses were tested in the unicellular cyanobacterium synechococcus PCC 7942 (R-2). Cells were exposed to hydrogen peroxide, cumene hydroperoxide and high light intensities. The extent and time course of oxidative stress were related to the activities of ascorbate peroxidase and catalase. Ascorbate peroxidase was found to be the major enzyme involved in the removal of hydrogen peroxide under the tested oxidative stress. Catalase activity was inhibited in cells, treated with high H2O2 concentrations, and was not induced under photooxidative stress. Catalase was specifically induced in cells treated with cumene hydroperoxide. Superoxide dismutase activity increased under conditions generating superoxide, such as high light intensities. The induction of the antioxidative enzymes was light dependent and was inhibited by chloramphenicol.
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PMID:Oxidative stress responses in the unicellular cyanobacterium Synechococcus PCC 7942. 190 71

The spectral (e.p.r. and absorbance) properties of the NO and deoxy derivatives of ferrous horseradish peroxidase (HRP; EC 1.11.1.7) and baker's-yeast cytochrome c peroxidase (CCP; EC 1.11.1.5) were investigated between pH 7 and pH 2; over the same pH range the kinetics for CO binding were also determined. At neutral pH the e.p.r. and absorption spectra of the NO and deoxy derivatives of HRP and CCP are typical of systems in which the haem iron is in the hexaco-ordinated state and the pentaco-ordinated state respectively. By lowering pH, the e.p.r. and absorption spectra of HRP and CCP undergo reversible transitions, with pKa values of 4.1 for the NO derivatives and less than or equal to 3 for the deoxy derivatives of the ferrous forms. By analogy with O2-carrying proteins and haem model compounds, the pH-dependent spectral changes of HRP and CCP were interpreted as indicative of the protonation of the N(epsilon) atom of the proximal histidine residue and of the cleavage of the Fe-N(epsilon) bond. However, the slow second-order rate constant (0.003 microM-1.s-1) for CO binding to deoxy ferrous HRP and CCP does not increase substantially even at pH 2.6, suggesting that changes in the Fe-haem plane geometry, presumably associated with the cleavage of the Fe-N(epsilon) bond, do not affect appreciably the observed ligand association rate constant.
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PMID:pH effects on the haem iron co-ordination state in the nitric oxide and deoxy derivatives of ferrous horseradish peroxidase and cytochrome c peroxidase. 253 9

Resonance Raman (RR) spectra for the resting state ferric and the reduced ferrous forms of recombinant Coprinus cinereus peroxidase (CIP), obtained with different excitation wavelengths and in polarized light, are reported. The spectra are compared with those obtained previously for cytochrome c peroxidase expressed in Escherichia coli [(CCP(MI)] and horseradish peroxidase (HRP-C). Although the enzymic properties of CIP and HRP-C are similar, the RR data show that, in terms of the heme cavity structures, CIP and CCP(MI) are much more closely related to each other than to HRP-C. The ferric state of CIP at neutral pH is characteristic mainly of a five-coordinate high spin heme. However, the lower frequency of the v2 mode and a higher frequency of the v(C = C) vinyl stretching modes for CIP as compared to CCP, indicate a higher degree of vibrational coupling between the two modes in CIP. In addition, CIP is rather unstable under low laser power irradiation as an irreversible transition to a six-coordinate high spin heme followed by a second transition to a six-coordinate low spin heme is observed. This instability of CIP as compared to CCP(MI) is proposed to be a consequence of the presence of a distal Phe54 in CIP rather than the homologous Trp51 in CCP, as Trp51 is hydrogen-bonded to a distal water molecule located above the heme Fe thereby preventing its coordination in CCP. In CIP the FeII-His RR band has two components with frequencies at 230 and 211 cm-1.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Resonance Raman study of the active site of Coprinus cinereus peroxidase. 780 6

Synechococcus PCC 7942, a cyanobacterium, possesses catalaseperoxidase as the sole hydrogen peroxide-scavenging system. The enzyme has been purified to electrophoretic homogenenity from the cells. The native enzyme had a molecular mass of 150 kDa and was composed of two identical subunits of molecular mass 79 kDa. The apparent Km value of the catalase activity for H2O2 was 4.2 +/- 0.27 mM and the kcat value was 2.6 x 10(4) s-1. The enzyme contained high catalase activity and an appreciable peroxidase activity with o-dianisidine and pyrogallol. The catalase activity was not inhibited by 3-amino-1,2,4-triazole but by KCN and NaN3 (apparent Ki values 19.3 +/- 0.84 and 20.2 +/- 0.95 microM respectively). The enzyme showed an absorption spectrum of typical protohaem and contained one protohaem molecule per dimer. The gene encoding catalase-peroxidase was cloned from the chromosomal DNA of Synechococcus PCC 7942. A 2160 bp open reading frame (ORF), coding a catalase-peroxidase of 720 amino acid residues (approx. 79.9 kDa), was observed. The deduced amino acid sequence coincided with that of the N-terminus of the purified enzyme and showed a remarkable similarity to those of a family of catalase-peroxidases of prokaryotic cells. Escherichia coli BL21 (DE3)plysS, harbouring a recombinant plasmid containing the catalase-peroxidase gene, produced a large amount of proteins that co-migrated on SDS/PAGE with the native enzyme. The recombinant enzyme showed the same ratio of catalase activity to peroxidase activity with o-dianisidine and the same Km for H2O2 as the native enzyme.
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PMID:The catalase-peroxidase of Synechococcus PCC 7942: purification, nucleotide sequence analysis and expression in Escherichia coli. 864 14

A cytosolic catalase-peroxidase from the cyanobacterium Synechocystis PCC 6803 was purified to homogeneity by a six-step purification procedure. It is a homodimeric enzyme with a subunit molecular mass of 85 kDa. The isoelectric point of the protein is at pH 5.5; Michaelis constant, turnover number, and catalytic efficiency of the catalase activity for H2O2 were measured to be 4.8 mM, 3450 s-1, and 7.2 x 10(5) M-1 s-1, respectively. Preparation and spectroscopy of the pyridine ferrohemochrome identified an iron protoporphyrin IX as the prosthetic group. The enzyme was shown to exhibit both catalase and peroxidase activities, both of which were inhibited by cyanide, leading to a high-spin to low-spin transition of the heme iron center as detected by a shift of the Soret peak from 405 to 421 nm. The catalase-specific inhibitor 3-amino-1,2,4-triazole proved ineffective. o-Dianisidine, pyrogallol and guaiacol functioned as a peroxidatic substrate, but no reaction was detected with NADH, NADPH, glutathione, and ascorbate. Peptide mass mapping using matrix assisted laser desorption ionization time-of-flight mass spectrometry showed the identity between the purified protein and a putative katG gene derived from the genome of Synechocystis PCC 6803. A comparison of amino acid sequences of the catalase-peroxidase from Synechocystis PCC 6803 and those from other bacteria showed a high homology around the assumed distal and proximal histidine residues, suggesting a highly conserved histidine as the fifth ligand of the heme iron.
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PMID:Purification and characterization of a hydroperoxidase from the cyanobacterium Synechocystis PCC 6803: identification of its gene by peptide mass mapping using matrix assisted laser desorption ionization time-of-flight mass spectrometry. 991 46

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.
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PMID:In vivo role of catalase-peroxidase in synechocystis sp. strain PCC 6803. 1007 82

The Synechocystis PCC 6803 katG gene encodes a dual-functional catalase-peroxidase (EC 1.11.1.7). We have established a system for the high level expression of a fully active recombinant form of this enzyme. Its entire coding DNA was extended using a synthetic oligonucleotide encoding a hexa-histidine tag at the C-terminus and expressed in Escherichia coli [BL21-(DE3)pLysS] using the pET-3a vector. Hemin was added to the culture medium to ensure its proper association with KatG upon induction. The expressed protein was purified to homogeneity by two chromatography steps including a metal chelate affinity and hydrophobic interaction chromatography. The homodimeric acidic protein (pl = 5.4) had a molecular mass of 170 kDa and a Reinheitszahl (A406/A280) of 0.64. The recombinant protein contained high catalase activity (apparent Km = 4.9 +/- 0.25 mM and apparent kcat = 3500 s(-1)) and an appreciable peroxidase activity with o-dianisidine, guaiacol and pyrogallol, but not with NAD(P)H, ferrocytochrome c, ascorbate or glutathione as electron donors. By using both conventional and sequential stopped-flow spectroscopy, formation of compound I with peroxoacetic acid was calculated to be (8.74 +/- 0.26) x 10(3) M(-1) s(-1), whereas compound I reduction by o-dianisidine, pyrogallol and ascorbate was determined to be (2.71 +/- 0.03) x 10(6) M(-1) S(-1), (8.62 +/- 0.21) x 10(4) M(-1) S(-1), and (5.43 +/- 0.19) x 10(3) M(-1) S(-1), respectively. Cyanide binding studies on native and recombinant enzyme indicated that both have the same heme environment. An apparent second-order rate constant for cyanide binding of (4.8 +/- 0.1) x 10(5) M(-1) S(-1) was obtained.
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PMID:Catalase-peroxidase from the cyanobacterium Synechocystis PCC 6803: cloning, overexpression in Escherichia coli, and kinetic characterization. 1054 46

Peroxidases are enzymes that utilize hydrogen peroxide to oxidize substrates. A histidine residue on the proximal side of the haem iron ligates most peroxidases. The various oxidation states and ligand complexes have been spectroscopically characterized. HRP-I is two oxidation states above ferric HRP. It contains an oxoferryl (= oxyferryl) iron with a pi-radical cation that resides on the haem. HRP-II is one oxidation state above ferric HRP and contains an oxoferryl iron. HRP-III is equivalent to the oxyferrous state. Only compounds I and II are part of the peroxidase reaction cycle. CCP-ES contains an oxoferryl iron but the radical cation resides on the Trp-191 residue and not on the haem. CPO is the only known peroxidase that is ligated by a cysteine residue rather than a histidine residue, on the proximal side of the haem iron. CPO is a more versatile enzyme, catalysing numerous types of reaction: peroxidase, catalase and halogenation reactions. The various CPO species are less stable than other peroxidase species and more elusive, thus needing further characterization. The roles of the amino acid residues on the proximal and distal sides of the haem need more investigation to further decipher their specific roles. Haem proteins, especially peroxidases, are structure-function-specific.
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PMID:Haem iron-containing peroxidases. 1073 Jan 88


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