Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.11.1.7 (peroxidase)
65,474 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The specificity of lactoperoxidase-catalyzed iodination for the proteins of the hepatoma tissue culture cell plasma membrane was examined by histochemical, biochemical, and cell fractionation techniques. Light microscope autoradiography of sectioned cells shows the incorporated label to be localized primarily at the periphery of the cell. Most of this label can be released from the cell by trypsin but not by collagenase or hyaluronidase. The label is recovered from the cells as either monoiodotyrosine or diiodotyrosine after hydrolysis of cell extracts with a mixture of proteolytic enzymes. The label co-purifies during cell fractionation with an authentic liver cell plasma membrane marker enzyme, 5'-nucleotidase. Thus, the incorporated iodide is itself a valid marker for those membrane polypeptides having tyrosine residues accessible to the lactoperoxidase. The polypeptide complexity of the purified plasma membrane was examined by high resolution dodecyl sulfate-polyacrylamide gel electrophoresis. At least 50 polypeptides in the membrane are accessible to iodination. These polypeptides probably represent the bulk of the protein mass of the membrane and iodinating them does not affect cell viability, growth rate, or cell function. Labeling experiments with fucose and glucosamine show that at least nine of the iodinated peptides may be glycoproteins.
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PMID:Proteins of the hepatoma tissue culture cell plasma membrane. 0 57

To produce a 125I-labelled glucagon suitable for radioligand assays, we studied the influence of variations in the lactoperoxidase iodination method. Both the degree of iodine substitution and the formation of monoiodo- or diiodo-tyrosines were pH dependent. The substitution increased and the diiodo-/monoiodotyrosine ratio decreased when pH increased. These two factors affected the immunoreactivity of the iodoglucagon relatively independently of each other. It was found that iodination at pH 10.0 with an average of 0.3 gatom I/mol glucagon resulted in 125I-labelled glucagon with higher immunoreactivity and stability than that produced at the conventional pH 7.5 and 8.5.
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PMID:Improved radioiodination of glucagon with the lactoperoxidase method. Influence of pH on iodine substitution. 0 74

Synthetic porcine secretion was labelled by the conjugation-labelling method of Bolton & Hunter, the lactoperoxidase method, the gaseous diffusion method, and the chloramine-T method. The chloramine-T technique was adapted as routine method. Ten mug (3.27 nmol) peptide was reacted with 5 mCi of Na125I at a concentration of chloramine-T of 1.3 mmol/l. Synthetic secretin was suitable for labelling for at least eight months when stored as dry matter in nitrogen-filled glass ampoules. Purification and separation of labelled from unlabelled hormone was carried out by gel-permeation chromatography on Sephadex G-50 superfine. The labelled preparation had a specific radioactivity of 405 +/- 33 muCi/nmol (mean +/- SEM., n = 9) and was unable for six days. 6-tyrosyl-secretin took more iodine compared to porcine synthetic secretin but had lower immunoreactivity with all antisera tested.
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PMID:Preparation of 125I-labeled synthetic porcine secretin for radioimmunoassay. 1 92

Trypsin-solubilized peroxidase activity from beef subcellular particles was resolved by DEAE-cellulose chromatography into 5 fractions, which contained enzymatically active components that ranged in molecular size from 73,000 to 340,000 daltons. The most active fraction (mol wt, 92,000 by gel filtration) was further purified (59,000-fold overall) by chromatography on hydroxylapatite. This highly purified peroxidase preparation had an absorbance purity ratio (A410:A280) of 0.55 and oxidized iodide (I3-formation) and guaiacol at rates of 300 and 460 micronmol/min/mg, respectively, which were about 3 and 1 1/2 times, respectively, greater than any previously described preparations. The enzyme was contaminated with an inactive protein of equal size. The highly purified peroxidase preparation lost its activity within a few days even when stored at -15 C with iodide. Two of the other DEAE-cellulose fractions contained peroxidase components with estimated sizes (gel filtration) of 73,000, 96,000, and 98,000, which were further purified purified (1,600 and 15,600 fold) on hydroxylapatite. They were 1/4 to 1/40 as active as the highly purified preparation and also became increasingly labile on purification. The remaining two DEAE-cellulose fractions were heterogeneous mixtures of stable peroxidase components whose average molecular sizes (gel filtration) were 220,000, 300,000, and 340,000 daltons, and which were not amenable to further purification on hydroxylapatite. The ratio of guaiacol to iodide activity decreased from 3.0 in the particles to about 1.5 in the highly purified preparations. The turnover numbers of the purest peroxidase component (mol wt. 92,000) for iodide and guaiacol were very similar to those of highly purifed, commericial lacto- and horseradish peroxidases. The pH maxima for iodide oxidation were 7.4, 6.0, and 4.5 for thyroid, lacto-, and horseradish peroxidases, respectively, whereas guaiacol oxidation peaked at pH 7.0-7.8 for all three enzymes. On the basis of these results and the dissimilar molecular sizes reported for trypsin-solubilized thyroid peroxidase by several other investigators, it was concluded that the molecular size is primarily determined by the conditions of proteolysis.
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PMID:Purification of bovine thyroid peroxidase. 1 22

This report describes the conditions that are necessary for iodination of staphylococcal enterotoxin B (SEB) by use of chloramine-T. Makor Chemical Co. SEB and the two major SEB components, which were prepared by isoelectric focusing of partially purified SEB, were used in these studies. The antigenic activity of the SEB preparations was monitored by radioimmunoassay as the oxidation/reduction (O/R) potential was increased by addition of chloramine-T. The SEB preparations lost antigenic activity rapidly at pH 7.5 and room temperature when sufficient chloramine-T was added to raise the O/R potential above 250 mV. Iodinated SEB with satisfactory immunoreactivity was prepared by omitting carrier iodide from the iodination reaction mixture and by using at least 1 mg of SEB/ml, steps which made the O/R potential more stable, and by stopping the reaction before the O/R potential exceeded 250 mV. Comparison of the chloramine-T method with a lactoperoxidase/H2O2 method of iodinating SEB showed the latter to cause a greater loss of immunoreactivity.
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PMID:Iodination of staphylococcal enterotoxin B by use of chloramine-T. 1 66

Indoleamine 2,3-dioxygenase was purified from rabbit small intestine to apparent homogeneity as judged by polyacrylamide gel electrophoresis and analytical ultracentrifugation. The native enzyme was a monomeric protein of a molecular weight of 41,000 +/- 1,000 with an s020,w value of 3.45 S. It had a relative abundance of hydrophobic amino acids such as valine, leucine, and isoleucine, and contained approximately 5% carbohydrate by weight. The estimated content of sugar residues per mol of enzyme was: galactose, 1.2; mannose, 2.6; N-acetylglucosamine, 5.2; and sialic acid, 0.8. One mole of enzyme had 0.8 mol of protoheme IX as a prosthetic group. However, copper was not detected in a significant amount and the ratio of copper to heme was less than 0.03. EPR spectra of the nitric oxide complex of the ferrous enzyme indicated that a nitrogen atom, possibly in an imidazole group, might be coordinated as the fifth ligand of the heme coenzyme. The anisotropic g values were gx = 2.08, gy = 1.98, and gz = 2.01. A single enzyme protein catalyzed the oxygenative ring cleavage of D- and L-tryptophan, D- and L-5-hydroxytryptophan, tryptamine, and serotonin. In addition, the purified enzyme had a peroxidase activity with guaiacol and potassium iodide as hydrogen donors, but not a catalase activity.
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PMID:Indoleamine 2,3-dioxygenase. Purification and some properties. 2 87

Glutathione and cysteine bind to the heme of lactoperoxidase, thereby causing a red shift of the Soret band which is reversed upon addition of iodide or guaiacol, two substrates for lactoperoxidase. The rate of formation of the enzyme-thiol complex is enhanced by diiodotyrosine. Binding of diiodotyrosine to lactoperoxidase does not cause a shift of the Soret band which indicates binding to the protein of the enzyme. At neutral pH and low ionic strength, lactoperoxidase is adsorbed on insolubilized diiodotyrosine (diiodotyrosine-agarose). It can be eluted at slightly increased ionic strength which shows that the binding is weak. In the presence of 5 X 10(-4) M glutathione, however, the binding of the enzyme to diiodotyrosine-agarose becomes much stronger so that a high salt concentration is required for elution. Lactoperoxidase is also adsorbed on insolubilized thiols (thiol-agarose). The presence of diiodotyrosine is not required for strong binding. A simple method for the preparation of lactoperoxidase from milk by affinity chromatography is based on the interactions of the enzyme with the two ligands, thiols and diiodotyrosine.
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PMID:Interaction of lactoperoxidase with thiols and diiodotyrosine. 3 12

The spectrophotometric method is described for the peroxidase activity determination which is based on the oxidation of guaicol and potassium iodide. Optimal conditions were elaborated for these two most sensitive substrates. The method may be applied for the quantitative peroxidase determination in different human biological fluids, in particular saliva and blood serum.
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PMID:[Method for determining peroxidase activity]. 3 24

An in vitro method employing an iodide-specific electrode for monitoring lactoperoxidase-catalyzed iodination is described. The method utilized lactoperoxidase, potassium iodide, and a glucose--glucose oxidase system for the generation of hydrogen peroxide and l-tyrosine. As iodination of l-tyrosine proceeded, the free iodide concentration in solution decreased and was monitored by an iodide-specific electrode. The iodide electrode was reliable when compared to a 131I-method for measuring free iodide changes in solution. Increasing concentrations of resorcinol, a well-known inhibitor of thyroid peroxidase-catalyzed iodination, in the reaction mixture resulted in graded inhibition of the initial rate of lactoperoxidase-catalyzed l-tyrosine iodination. This in vitro system can be used to assess inhibitory activity of various antithyroid substances.
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PMID:Use of an iodide-specific electrode to study lactoperoxidase-catalyzed iodination of l-tyrosine. 4 87

None of the radionuclides with which bleomycin has been labeled have chemical and nuclear properties that are entirely satisfactory for in vivo tumor localization. Bleomycin has been radioiodinated by the iodine monochloride, chloramine-T, and lactoperoxidase methods. Iodine monochloride proved to be the preferred method and conditions were developed whereby 80% of radioiodide was covalently bound to bleomycin. Bleomycin (140 mug) was added to 200 mul of saline/citrate buffer (pH 7.0) followed by radioiodide and iodine monochloride. This reaction mixture was incubated for 1 hr and purified by Sephadex G-10 chromatography. The iodine monochloride reaction product underwent hydrolytic deiodination in vitro at a rate of about 1.2%/day (0.15 M NaCl, 37 degrees C). Bleomycin A and B components were radioiodinated with equal efficiency on a mole fraction basis.
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PMID:Preparation and chemical characterization of radioiodinated bleomycin. 5 Oct 79


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