Search PubMed⌕ Search

Biomedical subjects

I Yamazaki

Publications and source records attributed to I Yamazaki.

At least 109 records · Page 6Linked to original sources
PubMed1986

Oxygen exchange between the Fe(IV) = O heme and bulk water for the A2 isozyme of horseradish peroxidase.

Resonance Raman spectra were observed for compound II of horseradish peroxidase A2, and the Fe(IV) = O stretching Raman line was identified at 775 cm-1. This Raman line shifted to 741 cm-1 upon a change of solvent from H2(16)O to H2(18)O, indicating occurrence of the oxygen exchange between the Fe(IV) = O heme and bulk water. The oxygen exchange took place only at the acidic side of the heme-linked ionization with pKa = 6.9.

Catalysis↗
PubMed1986

Characterization of one- and two-electron oxidations of glutathione coupled with lactoperoxidase and thyroid peroxidase reactions.

Glutathione (GSH) was oxidized to GSSG in the presence of H2O2, tyrosine, and peroxidase. During the GSH oxidation catalyzed by lactoperoxidase, O2 was consumed and the formation of glutathione free radical was confirmed by ESR of its 5,5'-dimethyl-1-pyrroline-N-oxide adduct. When lactoperoxidase was replaced by thyroid peroxidase in the reaction system, the consumption of O2 and the formation of the free radical became negligibly small. These results led us to conclude that, in the presence of H2O2 and tyrosine, lactoperoxidase and thyroid peroxidase caused the one-electron and two-electron oxidations of GSH, respectively. It was assumed that GSH is oxidized by primary oxidation products of tyrosine, which are phenoxyl free radicals in lactoperoxidase reactions and phenoxyl cations in thyroid peroxidase reactions. When tyrosine was replaced by diiodotyrosine or 2,6-dichlorophenol, the difference in the mechanism between lactoperoxidase and thyroid peroxidase disappeared and both caused the one-electron oxidation of GSH. Iodides also served as an effective mediator of GSH oxidation coupled with the peroxidase reactions. In this case the two peroxidases both caused the two-electron oxidation of GSH.

Animals↗
PubMed1986

Calcitonin secreting property of ipriflavone in the presence of estrogen.

Calcitonin secretion is influenced by estrogen. In the present study, basal and calcium-stimulated serum calcitonin levels were reduced in ovariectomized rats, and replacement estrogen administered for 3 weeks increased both calcitonin levels to those in intact rats. Ipriflavone, 7-isopropoxy-3-phenyl-4H-1-benzopyran-4-one, alone did not influence either calcitonin level. However, ipriflavone and subeffective doses of estrogen administered simultaneously increased both levels; the increase depended upon the dose of ipriflavone. Furthermore, pretreatment with estrone resulted in greater calcitonin release in response to various doses of calcium and pretreatment with estrone and ipriflavone caused an even greater release. These findings indicate that ipriflavone increases the sensitivity of the thyroid gland to estrogen to secrete calcitonin in response to calcium.

Animals↗
PubMed1986

Effect of ipriflavone on glucocorticoid-induced osteoporosis in rats.

Ipriflavone, 7-isopropoxy-3-phenyl-4H-1-benzopyran-4-one, was administered orally for 12 weeks to male rats with prednisolone-induced osteoporosis. Microdensitometric analysis of a roentgenograph of the femurs revealed that ipriflavone increased the density of the distal metaphysis dose-dependently and tended to increase the density of the diaphysis. It also inhibited dose-dependently the decrease in the mechanical strength of the tibia, breaking strain and breaking energy, and the fractional content of ash in femurs. These results indicate that ipriflavone markedly suppresses bone resorption at the metaphysis where the content of trabecular bone with a rapid turnover rate is high, and possibly inhibits bone reduction at the diaphysis.

Animals↗
PubMed1986

Effect of ipriflavone on the response of uterus and thyroid to estrogen.

Ipriflavone, 7-isopropoxy-3-phenyl-4H-1-benzopyran-4-one, was uterotropic in intact but not in ovariectomized rats. When it was administered simultaneously with estrone and estradiol-17 beta to ovariectomized rats, ipriflavone increased the uterotropic activities of both estrogens. The uterotropic activity of this compound in intact rats might be attributable to its action on the target organ of estrogen by augmenting the response to the hormone because none of the other possibilities for accelerating uterine growth such as gonadotropin-releasing, gonadotropic, and estrogen metabolism-retarding activities were demonstrated experimentally. In addition, ipriflavone increased the calcitonin releasing activity of estrone when these compounds were administered simultaneously to ovariectomized rats.

Animals↗
PubMed1986

The sustained release of LH X RH agonist from LH X RH agonist-polymer composite in patients with prostatic cancer.

Luteinizing hormone-releasing hormone (LH X RH) agonist can be administered daily to patients with prostatic cancer with resulting clinical efficacy. A sustained drug release formulation of an LH X RH agonist, (D-Leu6)-des Gly-NH2(10)-LH X RH ethylamide (leuprolide)-vinyl polymer composite, was prepared by means of radiation-induced polymerization under a supercooled state. The sustained release of leuprolide from subcutaneously implanted leuprolide-vinyl polymer composite (14 mm in diameter and 4 mm in thickness) was obtained over a period of several months in five patients with prostatic cancer. Serum testosterone levels began to decrease on the tenth day, fell below 1 ng/ml after three weeks of implantation, and thereafter remained at the castration level until removal of the polymer composite. Clinical improvement was associated with serum hormonal changes, and support this as a novel and superior method of administration of LH X RH agonist.

Aged↗
PubMed1986

The 2-electron reduction of sperm whale ferryl myoglobin by ethanol.

Upon the addition of hydrogen peroxide or ethyl hydroperoxide to sperm whale metmyoglobin (MbIII) in the presence of ethanol, MbIII was converted to oxymyoglobin (MbIIO2) under aerobic conditions and carboxymyoglobin (MbIICO) under CO-saturated conditions. MbIIO2 and MbIICO were also formed when ethanol was added to ferryl myoglobin (MbIV) which had been formed from the reaction of MbIII with hydrogen peroxide. From the stoichiometry, the primary reaction was formulated as follows. MbIV + ethanol----MbII + acetaldehyde The reaction was optimal at pH 7.0-7.5. Sperm whale ferryl myoglobin was reduced less effectively by methanol and n-butanol, but not at all by sec- and tert-butanols. The reduction of ferryl hemoproteins by ethanol was slower with horse heart myoglobin and was not observed with bovine hemoglobin or horseradish peroxidase.

Animals↗
PubMed1985

Photooxidation of porphyrin in Mg-substituted horseradish peroxidase.

Upon photoirradiation under aerobic conditions, the porphyrin prosthetic group in Mg-substituted horseradish peroxidase was oxidized to a mixture of its pi-cation radical and an oxidized product with an absorption band at 448 nm. The 448 nm compound was then converted to a 489 nm compound in the dark and the activation energy for the conversion was 19.3 kcal/mol. About 1 mol of O2 was consumed per mol of the 448 nm compound formed and no O2 consumption was seen in the dark reaction. The substitution of ethyl groups (meso) and hydroxyethyl groups (hemato) for the vinyl groups in protoporphyrin IX did not have an effect on the result. Under anaerobic conditions and in the presence of a suitable electron acceptor, the only photooxidation product of porphyrin was its pi-cation radical. The formation of hydroxyl radicals during irradiation under aerobic conditions was confirmed by the spin-trapping method. The formation of the above two radicals could be followed by ESR spectroscopy separately at a fixed magnetic field which was set to maximize each ESR signal. The rate of hydroxyl radical formation depended linearly on the concentration of Mg peroxidase. The photooxidation of porphyrin was slow and gave nonspecific product(s) when Mg protoporphyrin IX was present in the heme crevice of apomyoglobin or free in solution.

Electron Spin Resonance Spectroscopy↗
PubMed1985

Thyroid peroxidase selects the mechanism of either 1- or 2-electron oxidation of phenols, depending on their substituents.

Unlike lactoperoxidase and horseradish peroxidase, thyroid peroxidase catalyzed the oxidation of hydroquinone mostly by way of 2-electron transfer. This conclusion could be derived from three independent experiments: ESR measurements of p-benzosemiquinone, trapping the unpaired electron by cytochrome c, and spectrophotometric analysis of catalytic intermediates of the enzymes. The 1-electron flux for hydroquinone oxidation was found to be 15-19% in the reaction of thyroid peroxidase, while it was nearly 100% in the reactions of lactoperoxidase and horseradish peroxidase. From the spectrophotometric analysis of the catalytic intermediates of enzyme, it was suggested that the mechanism of oxidation catalyzed by thyroid peroxidase changes from a 2-electron to a 1-electron type as the substituents at 2- and 6-positions of phenol become bulky or heavy. On the other hand, the mechanism was invariably a 1-electron type when the oxidation of phenols was catalyzed by lactoperoxidase or horseradish peroxidase. These three peroxidases all catalyzed 1-electron oxidation of ascorbate.

Animals↗
PubMed1985

Detection of a catalytic intermediate of peroxidase in hog thyroid microsomes.

A catalytic intermediate, Compound II of peroxidase was detected spectrophotometrically in thyroid microsomes. From comparison with the spectral data on purified thyroid peroxidase, the content of the peroxidase was estimated to be 0.019 nmol per mg of the microsomal protein, being about one-eighth of the amount of cytochrome b5. It was concluded that thyroid peroxidase exhibits the same peroxidase activity for guaiacol or ascorbate in the free and the microsome-bound forms.

Animals↗
PubMed1985

Spectra of chloroperoxidase compounds II and III.

Chloroperoxidase was present as Compound II during the peroxidatic oxidation of ascorbic acid. Compound III (oxy-form) was formed when excess hydrogen peroxide was added to Compound II. By decreasing the temperature it was possible to measure the spectra of Compounds II and III in the Soret and visible regions. Each spectrum was found to resemble that of the corresponding form of lactoperoxidase. Under the experimental conditions, chloroperoxidase Compound III was apparently converted to Compound II in parallel with the decomposition of hydrogen peroxide and finally to the ferric enzyme.

Ascorbic Acid↗
PubMed1985

Purification of thyroid peroxidase by monoclonal antibody-assisted immunoaffinity chromatography.

A rapid method was developed for purification of hog thyroid peroxidase by immunoaffinity chromatography on a column of Sepharose 4B coupled to a monoclonal antibody to the peroxidase. The purified enzyme had a specific activity of 194 units/mg and showed the same absorption spectrum in the Soret and visible regions as that of the enzyme purified after trypsin treatment. The ratio of A413 nm to A280 nm was 0.24, being much less than that for the trypsinized enzymes. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, it gave a broad protein band in the 100,000-dalton region. It is concluded that the preparation purified in this study represents a native form of thyroid peroxidase.

Animals↗
PubMed1985

Characterization of hog thyroid peroxidase.

Several fundamental properties of purified hog thyroid peroxidase (A413 nm/A280 nm = 0.55) were investigated in comparison with bovine lactoperoxidase. The Mr of thyroid peroxidase was 71,000. The prosthetic group of thyroid peroxidase was identified spectrophotometrically as protoheme IX after the enzyme was hydrolyzed with Pronase. Optical spectra of oxidized and reduced thyroid peroxidases and their complexes with azide and cyanide were very similar to lactoperoxidase, except that lactoperoxidase had two reduced forms with the Soret band either at 446 or 435 nm, and thyroid peroxidase lacked a reduced form having the 446-nm band. From comparison of their pyridine hemochrome spectra, epsilon mM at 413 nm of thyroid peroxidase was estimated to be 114, being the same as that of lactoperoxidase. The cyanide inhibition for the reaction of thyroid peroxidase was competitive with hydrogen peroxide and the inhibition constant was in rough accord with the dissociation constant of its cyanide complex measured from spectrophotometric titration. Azide inhibited the reaction with an inhibition constant which was about one one-thousandth of the dissociation constant for its spectrally discernible complex. The azide inhibition was not competitive with hydrogen peroxide and decreased as the reaction proceeded. Aminotriazole inhibited the reaction strongly, and the inhibition was augmented during the reaction. These inhibition patterns of azide and aminotriazole were more or less observed in the reaction of lactoperoxidase, but not in the case of horseradish peroxidase. Characteristics of animal peroxidases are discussed.

Animals↗
PubMed1985

Physiological aspects of free-radical reactions.

Enzymes which catalyze the formation of free radicals in vitro will catalyze similar reactions in vivo. We believe that the formation of some kinds of free radicals has definite physiological meanings in metabolism. In this sense, the enzymes forming such free radicals are concluded to be in evolutionally advanced states. Elaborated structure and function of enzymes such as horseradish peroxidase and microsomal flavoproteins support the idea. Deleterious and side reactions caused by free radicals are assumed to be minimized in vivo by localizing the reactions, but this assumption should be verified by future studies.

Animals↗
PubMed1984

Reactions of ferryl lactoperoxidase (compound II) with sulfide and sulfhydryl compounds.

Lactoperoxidase in the ferryl state (compound II) reacts with sulfide to form a typical sulfheme -containing hemoprotein as do hemoglobin, myoglobin, and catalase. Ferrous sulflactoperoxidase is primarily formed and then oxidized to its ferric form under aerobic conditions. Similar reactions of lactoperoxidase occurs when methylmercaptoimidazole (MMI) is substituted for sulfide. The yield of the adducts from one-turnover reactions of ferryl lactoperoxidase is 100% with sulfide and about 20% with MMI. Sulfur and MMI of the adducts appear to be removed from the enzyme upon reduction by dithionite. Upon the reactions with cysteine and dithiothreitol, the enzyme is converted to spectral species, which are less characteristic but are similar to ferrous and ferric sulflactoperoxidases , respectively. We conclude that there is no essential difference in the mechanism of reactions of lactoperoxidase with sulfide, MMI, cysteine, and dithiothreitol.

Animals↗
PubMed1984

Iodination and oxidation of thyroglobulin catalyzed by thyroid peroxidase.

The kinetics of iodination and oxidation of hog thyroglobulin were studied with purified hog thyroid peroxidase and the results were compared with the reactions of free tyrosine. From Lineweaver-Burk plots and on the basis of a value of 0.83 for delta epsilon mM at 289 nm/iodine atom incorporated, the rate constant for transfer of an assumed enzyme-bound iodinium cation to thyroglobulin was estimated to be 6.7 X 10(7) and 2.3 X 10(7) M-1 s-1 in native (iodine content = 1.0%) and more iodinated (iodine content = 1.2%) thyroglobulins, respectively. This iodine-transferring reaction was stimulated by iodothyronines, similarly as observed in the reaction with free tyrosine. The iodination of thyroglobulin was inhibited by GSH, the inhibition being competitive with thyroglobulin. Thyroglobulin was oxidized in the presence of a thyroid peroxidase system without giving any appreciable change in absorbance around 300 nm. From stopped flow data, the oxidation was concluded to occur by way of two-electron transfer and the rate constant for the reaction of thyroid peroxidase Compound I with thyroglobulin was estimated to be 1.0 X 10(7) M-1 s-1. The stopped flow kinetic pattern was similar to that observed on the reaction with free tyrosine and monoiodotyrosine. About 6 mol of hydrogen peroxide were consumed per mol of thyroglobulin. Thyroid peroxidase catalyzed thyroglobulin-mediated oxidation of GSH, but lactoperoxidase did not.

Animals↗