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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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

Prolactin iodinated by lactoperoxidase method showed immunologically, electrophoretically and biolo9gically similar properties to native prolactin and possessed enough specific radioactivity for receptor studies. 1251-prolactin was incubated with mouse mammary tissues at 8 days of lactation. Both binding and release of 1251-prolactin depended on incubation time and temperature and were maximal at 37 degrees C. Michaelis constant was estimated to be 1.4 X 10(-9) M from Lineweaver-Burk plot and to be 1.2 X 10(-9) M from id-value of the dose-response curve for displacement with native prolactin. Total number of binding sites for prolactin was 1.38 X 10(-15) mole per mg weight of tissue. Ovine prolactin, human growth hormone and human placental lactogen complete with 1251-prolactin and dose-response curves for these three hormones were all parallel. These results suggest the existence of a specific receptor site with high affinity for prolactin in lactating mouse mammary glands.
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PMID:A receptor site for prolactin in lactating mouse mammary tissues. 17 1

The lactoperoxidase-catalyzed oxidation of glutathione (GSH) and thiocyanate (SCN-) was studied. Oxidation of SCN- was recorded by ultraviolet spectroscopy and by electron spin resonance (ESR). Consumption of GSH was measured by amperometric titration. One or two moles of GSH was oxidized per mole of H2O2 added, depending on the reaction conditions. Omission of SCN- prevented the oxidation of GSH. The oxidation of GSH required only catalytic amounts of SCN-, which was therefore recycled. Iodide (I-) could replace SCN-, while chloride or bromide were ineffective. The apparent Michaelis constant for SCN- was 17 microM. Oxidation of SCN- gave rise to two reactive intermediates, one stable and one unstable. The stable intermediate (-OSC. = N-(?)) decayed by a second-order reaction with a rate constant of 1.1 M-1 s-1. The decay of the unstable radical was very fast. The data (a) explain the short- and long-term antibacterial effects of lactoperoxidase-halide-H2O2 system, (b) point to possible deleterious effects due to glutathione depletion, (c) are of relevance for free radical diseases involving sulphur-centered free radicals, and (d) support previous observations on lipid peroxidation/halogenation in biological membranes, liposomes, and unsaturated fatty acids.
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PMID:Free radical generation and coupled thiol oxidation by lactoperoxidase/SCN-/H2O2. 132 2

2-Thiazoline-2-thiol is an antithyroid agent that strongly reduces thyroid hormone levels. Synthesis of these hormones is catalyzed in vivo by thyroid peroxidase. The interaction of this drug with molecular iodine and its effect on peroxidase activity were investigated. Iodine and 2-thiazoline-2-thiol form a complex of the charge transfer type of 1:1 stoichiometry characterized by a formation constant of 2,527 l.mole-1 at 20 degrees C. This drug was found to inhibit both horseradish peroxidase and lactoperoxidase (used as a model of thyroid peroxidase) in a competitive manner, giving inhibition constants of 5.7 mM and 0.13 mM, respectively. T3 and T4 levels were reduced significantly after a three-week administration of this drug to a group of 10 rats. Histological examination of the thyroid gland showed the presence of a cylindrical epithelium, which is indicative of hyperactivity of the gland. The results indicated that 2-thiazoline-2-thiol acts on both molecular iodine and thyroid peroxidase.
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PMID:Sites of action of 2-thiazoline-2-thiol on biogenesis of thyroid hormones. 138 Sep 99

Direct evidence is presented in support of mechanism-based (suicide) inactivation of lactoperoxidase by thiocarbamide thyroid inhibitors. The turnover of 1-methylbenzimidazolidine-2-thione was demonstrated by identifying the inhibitor-derived products 1-methylbenzimidazole and bisulfite ion that are formed concurrent to enzyme inactivation. The turnover of a hydroperoxide cosubstrate, 5-phenyl-4-pentenyl hydroperoxide, was quantitated from formation of the corresponding alcohol during enzyme inactivation. A specific inactivation pathway is suggested by the covalent binding of 1 mol of 14C- and 35S-labeled benzimidazolidine-2-thione and 1-methylbenzimidazolidine-2-thione per mole of inactivated lactoperoxidase. These results are explained by partitioning of inhibitor-derived S-oxygenated intermediates between turnover and inactivation pathways. The properties of the inactivation process are unique among thiono-sulfur compounds and suggest that benzimidazolinesulfenic acids are the reactive intermediates.
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PMID:Mechanism-based inhibition of lactoperoxidase by thiocarbamide goitrogens. Identification of turnover and inactivation pathways. 245 91

1. Inhibition of lactoperoxidase by thiocarbamides is consistent with a suicide mechanism whereby enzyme-catalysed S-oxygenation produces reactive intermediates which covalently modify the active site haem. 2. The reaction of thiocarbamide goitrogens with lactoperoxidase in the presence of hydroperoxides results in time-dependent and irreversible enzyme inactivation and an altered visible spectrum of the haem prosthetic group of the inactivated enzyme. 3. A mechanism of S-oxygenation for the inactivation is suggested by lactoperoxidase-catalysed formation of stable S-oxides from thioamide and organosulphur functional groups, and by a common dependence of substrate and inhibitor binding constants on their electrochemical oxidation potentials. 4. Hydroperoxide-dependent inactivation of lactoperoxidase by benzimidazoline-2-thiones occurs concomitantly to the covalent binding of stoichiometric amounts of 14C- or 35S-labelled inhibitors per mole of enzyme, and the formation of turnover products derived from the hydroperoxide cosubstrate and inhibitor.
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PMID:Hydroperoxide-dependent metabolism of goitrogenic thiocarbamides by lactoperoxidase. 314 24

Aerobic or anaerobic degradation of glucose by Streptococcus dysgalactiae and Streptococcus uberis yielded products qualitatively similar to those observed previously for Streptococcus agalactiae. There were, however, quantitative differences. Though acetoin was formed during aerobic growth of Streptococcus uberis, there was none with Streptococcus dysgalactiae. Differences between Streptococcus dysgalactiae and Streptococcus uberis in their aerobic metabolism of glucose was in lower oxygen consumption (.5 mol/mol of glucose), greater conversion of glucose to lactic acid, and lower molar growth yields with Streptococcus uberis. Cell suspensions of Streptococcus uberis had strong peroxidase activity, and no hydrogen peroxide accumulated during the respiration on glucose. With Streptococcus dysgalactiae, there was more oxygen consumed during growth (1.5 mol/mol of glucose used), greater conversion of glucose to acetic and formic acids and carbon dioxide, and a cell yield of about 6 g of dry cells more per mole of glucose than with Streptococcus uberis. This increase in molar growth yield with Streptococcus dysgalactiae over Streptococcus uberis could be nearly all accounted for by differences in the amount of substrate level adenosine triphosphate generated. Cell suspensions oxidizing glucose accumulated hydrogen peroxide and showed no peroxidase activity. Streptococcus dysgalactiae showed the same growth relationships in three milk media as Streptococcus agalactiae, although growth and acid formation values were much lower. Growth inhibition by the lactoperoxidase complex was reversed with cystine. Acid formation by Streptococcus uberis was decreased by the lactoperoxidase complex and increased by the addition of cystine; however, neither appeared to affect the growth of the organism.
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PMID:Physiological characteristics of Streptococcus dysgalactiae and Streptococcus uberis and the effect of the lactoperoxidase complex on their growth in a chemically-defined medium and milk. 391 77

1. Binding of a purified scorpion toxin to membrane fragments isolated from electroplaque of an electric eel Electrophorus electricus was studied using a radio-iodinated toxin.2. A scorpion toxin was purified from the venom of Leiurus quinquestriatus and iodinated with (125)I in a lactoperoxidase-catalysed reaction. Monoiodinated toxin, isolated by an ion exchange chromatography, retarded the inactivation kinetics of Na current to a similar extent as the native toxin, indicating that radioiodination did not appreciably affect physiological and binding properties of the native toxin.3. Analyses of binding properties by Scatchard plots showed the presence of two classes of binding sites (with low and high affinities) in the membrane preparation from eel electroplaque; similar preparation from an electric skate, of which the electroplaque is known to be devoid of Na channels, possessed only the low affinity sites.4. The number of high affinity sites in the eel preparation was 41.8 +/- 10.5 p-mole/g tissue; the value was within the range reported for tetrodotoxin binding to similar preparations (15-148 p-mole/g tissue).5. A variety of cations (Na(+), Mn(2+) and La(3+)) inhibited the high affinity scorpion toxin binding, as indicated for the toxin binding to Na channels by a previous electrophysiological study. K(D) value in the presence of 120 mM-Na(+) (approx. 8 nM) agreed reasonably with that (approx. 10nM) reported for the scorpion toxin binding to excitable neuroblastoma cells or synaptic nerve ending particles under conditions where membrane potential was depolarized by the addition of 135 mM-KCl.6. Pretreatment of the eel membrane preparation with beta-bungarotoxin (7-44 ng/ml.) in the presence of Ca ions (10-200 muM) resulted in a substantial loss of high affinity binding of scorpion toxin. When phospholipase A(2) activity of the beta-toxin was inactivated by a chemical modification with p-bromophenacyl bromide, the inhibitory action of the beta-bungarotoxin was abolished.7. It is concluded that a high affinity binding of scorpion toxin to the eel electroplaque membrane fragments represents the binding to Na channels in vitro, and that phospholipase A(2) activity of beta-bungarotoxin interferes with the binding of scorpion toxin to Na channels.
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PMID:Binding of scorpion toxin to sodium channels in vitro and its modification by beta-bungarotoxin. 624 82

Cystine reduction in Streptococcus agalactiae, resulting in sulfhydryl formation, may account for antagonism of the antibacterial effect of lactoperoxidase-thiocyanate-hydrogen peroxide when cystine is present in excess of the amount needed for maximum growth. Accumulation of cystine by S. agalactiae and its reduction to form sulfhydryl compounds were demonstrated. The reduction of cystine appeared to occur by a couple reaction between glutathione reductase and glutathione-disulfide transhydrogenase activity, both of which were found in the supernatant fraction from cell homogenates. NADPH-specific glutathione reductase activity was found in the pellet and supernatant fractions from cell homogenates. Two sulfhydryls were formed for each mole of NADPH used during cystine reduction. The information presented offers a plausible explanation of how cystine, when present in excess of growth needs, may be reduced to generate sulfhydryl compounds which neutralize the antibacterial effect of lactoperoxidase-thiocyanate-hydrogen peroxide on S. agalactiae.
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PMID:Cystine antagonism of the antibacterial action of lactoperoxidase-thiocyanate-hydrogen peroxide on Streptococcus agalactiae. 637 Jan 35

The titration by ferrocyanide and the localization of the oxidizing equivalents of lactoperoxidase "compound II" were studied as a function of pH. It was demonstrated that 1) whatever the pH, the structure of lactoperoxidase "compound II" was compatible with a Fe IV R degree state, 2) at acidic pH, ferrocyanide preferentially reduced the oxidizing equivalent localized on the heme iron to give an Fe III R degree compound, 3) at pH 4.2 only the Fe III R degree form was obtained after reduction of lactoperoxidase "compound II" with one mole of ferrocyanide and whereas at pH greater than 4.2, a mixture of both Fe III R degree and Fe IV R forms was present, 4) lowering the pH from 7.2 to 4.0 induced a transition of Fe IV R state to Fe III R degree state, but increasing the pH from 4.0 to 7.2 did not permit the formation of Fe IV R compound from Fe III R degree compound.
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PMID:Reduction of lactoperoxidase-H2O2 compounds by ferrocyanide: indirect evidence of an apoprotein site for one of the two oxidizing equivalents. 637 71


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