共查询到20条相似文献,搜索用时 10 毫秒
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The isolated myenteric plexus-longitudinal muscle of the guinea-pig ilem (GPI) was used as testsystem to study the influence of chronic morphine treatment on the levels of enkephalins, β-endorphin and some of its fragments. The peptides were assayed by means of a combination of high pressure liquid chromatography and radioimmunoassays. It was found that the levels of methionine- and leucine-enkephalin and β-endorphin were not altered by chronic morphine treatment of guinea-pigs nor in GPI exposed to morphine . However, the levels of some β-endorphin fragments i.c. γ-endorphin and des-tyrosine-γ-endorphin were elevated after morphine treatment and respectively. It is suggested that β-endorphin and its fragments are involved in homeostatic processes during development of opiate tolerance. 相似文献
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Studies were conducted to determine the influence of some LHRH analogues on gonadotropic hormone (GtH) secretion in two species of trout. The observations indicated that synthetic LHRH and various stimulatory LHRH analogues are approximately equipotent in these fish. This is an unexpected result considering the superactive properties of these analogues demonstrated in mammals. An inhibitory LHRH analogue was also tested in the trout with the result that powerful inhibition of LHRH induced GtH release was obtained. 相似文献
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John W. Kendrick 《Theriogenology》1976,5(3):150-152
and : Herds infected with have histories of infertility, occasional abortions, and pyometra.: There are no specific gross lesions in the fetus. The fetuses are usually aborted in the first half of gestation and may or may not be accompanied by the placenta.: There are no specific microscopic lesions.: It is ordinarily not necessary to culture in order to demonstrate its presence in placental fluids and/or abomasal contents.: There are no suitable seroligic procedures for diagnosing Trichomoniasis.: Wet mounts of abomasal contents and/or placental fluids are examined microscopically for .: Demonstrate the presence of by microscopic examination of wet mounts of placental fluids and/or abomasal contents. 相似文献
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Studies were conducted to determine the fate of 15α-hydroxyprogesterone in human placental tissue. Tritiated 15α-hydroxyprogesterone was perfused through normal human placentas at the time of Cesarean section and incubated with a 10,000x g microsomal supernate of the placenta . In both systems the substrate, but no additional metabolites were identified. These findings indicate that 15α-hydroxyprogesterone is not metabolized during its passage in the human term placenta, and suggests that because of its fetal origin clinical measurements of 15α-hydroxyprogesterone may provide a valuable index to the status of fetal viability. 相似文献
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M. Thirunavukkarasu Fergus G. Priest 《Biochemical and biophysical research communications》1983,114(2):677-683
α-Glucosidase was membrane bound during exponential growth of but was released into the medium during stationary phase. It could be partially removed from exponential phase cells by washing with NaCl (0.5 M). α-Amylase was exclusively extracellular and could not be detected in cells. Polysomes were prepared from exponential phase cells and separated into membrane bound and soluble fractions. chain completion and immunoprecipitation showed that α-glucosidase and α-amylase were synthesized by membrane bound and not by soluble ribosomes. 相似文献
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Anthony L. Tarentino Frank Maley 《Biochemical and biophysical research communications》1975,67(1):455-462
The substrate specificities of the endo-β-N-acetylglucosaminidases from and were compared and found to differ considerably. The enzyme from released Asn-GlcNAc-Fuc-containing glycopeptides from exoglycosidase-treated acidic IgM glycopeptides but was limited in its capacity to hydrolyze ovalbumin glycopeptides larger than Asn(GlcNAc)2(Man)5. In contrast, the enzyme from hydrolyzed this and larger neutral oligosaccharides but could not hydrolyze the above fucose-containing IgM glycopeptides. Removal of the fucose residue, however, converted the latter to an active substrate for the enzyme, thus broadening its substrate range to encompass most of those substrates hydrolyzed by the endoglycosidase. 相似文献
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Robert L. Barbieri Rapin Osathanondh Jacob A. Canick Robert J. Stillman Kenneth J. Ryan 《Steroids》1980,35(3):251-263
The effects of danazol on steroidogenesis in the 16–20 week old human fetal adrenal were examined by studying: 1) danazol binding to adrenal microsomal and mitochondrial cytochrome P-450, and 2) enzyme kinetics of danazol inhibition of the adrenal microsomal 21-hydroxylase and the mitochondrial llβ-hydroxylase. The addition of danazol to preparations of adrenal microsomes or mitochondria elicited a type I cytochrome P-450 binding spectrum. Danazol bound to microsomal cytochrome P-450 with a high affinity apparent spectral dissociation constant (Kg) of 1 μM and with a lower affinity K's of 10 μM. Danazol bound to mitochondrial cytochrome P-450 with a Kg of 5 μM. In addition, danazol competitively inhibited the microsomal 21-hydroxylase (apparent enzymatic inhibition constant KI = 0.8 μM) and the mitochondrial 11β-hydroxylase (KI = 3 μM). These findings demonstrate that low concentrations of danazol directly inhibit steroidogenesis in the human fetal adrenal . 相似文献
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Yukio Imanishi Hiroyuki Ohnishi Yutaka Hashimoto 《International journal of biological macromolecules》1981,3(2):97-104
The enantiomer selection in the nucleophilic addition reaction of optically active amines such as α-amino acid esters to phenylalanine and in as a solvent has been investigated. Stereoselectivity between the amines and the was found to change markedly according to the reaction conditions. This experimental finding is in contrast to the idea hitherto accepted that in the nucleophilic addition-type polymerization of α-amino acid the growing chain end reacts preferentially with one of the enantiomorphic having the same configuration, and indicates the importance of the investigation of stereoselectivity in the polymerization using suitable model reactions. Most acid esters reacted preferentially with , and this type of stereoselectivity increased with the of and with increasing bulkiness of the Cα substituent of α-amino acid esters (alanine < norleucine < leucine < valine). The relationship observed between the stereoselectivity and the structures of amines and was explained satisfactorily in terms of the transition state model in which the interaction of nitrogen and α-amino acid ester carbonyl as well as the interaction of carbonyl and α-amino acid ester nitrogen was taken into account. ethyl ester did not show enantiomer selectivity toward phenylalanine , but reacted preferentially with . for the reaction of proline ester with a transition-state model was proposed, which was different from the transition state model proposed for other α-amino acid esters. Some experiments were carried out to examine the transition-state models proposed. The implications of the present investigation in stereoselectivity in the nucleophilic addition-type polymerization of hitherto reported are discussed. 相似文献
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The addition of cholic acid to growing cultures of species V.P.I. 12708 caused a 25 and 46-fold increase in 7α-dehydroxylation activity using cell extracts or whole cell suspensions, respectively. Bile acid conversion rates using either [14C]-cholic acid or [14C]-chenodeoxycholic acid as substrates increased at approximately the same rate when either cholic or chenodeoxycholic acid was added to growing cultures as inducer. The induction of 7α-dehydroxylase activity was highly specific requiring a free C-24-carboxyl group and an unhindered 7α-hydroxy group on the B ring of the steroid nucleus. Unexpectedly, cholic acid also rapidly induced NADH:flavin oxidoreductase activity in growing cultures of this bacterium. 相似文献
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Noriyuki Kuramoto Munenori Sakamoto Jiro Komiyama Toshiro Iijima 《International journal of biological macromolecules》1984,6(2):69-72
The interaction of α-chymotrypsin with poly(acrylic acid)s (PAA) having different stereoregularities and molecular weights has been studied through the effects of α-chymotrypsin on enzymic hydrolysis of acetate (NpOAc). The results show that isotactic PAA inhibits the hydrolysis more strongly than do atactic and syndiotactic PAAs. The inhibition constant or the dissociation constant of the reactio-inhibiting PAA α-chymotrypsin complex decrease with increasing molecular weight of PAA. 相似文献
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), (Me3Orn)n, is usually not able to attain the α-helical conformation in aqueous solution independent of its pH value; however, it becomes α-helical at low concentrations of sodium perchlorate over a wide pH range according to the circular dichorism (c.d.) spectra. Cl?, SO42? and H2PO4? do not induce α-helix formation. One can conclude that a distinct topology of the anions bound by the side chains is responsible for the α-helix-inducing effect of some water-structure-breaking anions such as perchlorate. This means that the anions are inserted between the ?N+ of the side groups shielding the positive charges repelling one another. The insertion of the anions requires that the water molecules surrounding the ions can be stripped off, which is easily possible if they are water-structure-breaking ones. At higher perchlorate concentrations, the c.d. spectrum changes. It is characterized by a negative shoulder near 208 nm and a pronounced minimum at ≈ 226 nm. With increasing temperature, the c.d. spectrum of the α-helix occurs. Finally the α-helix undergoes a conformational change to the random coil. The apparent transition enthalpy ΔHvH is remarkably lower than that of the homologue (Me3Lys)n, obviously due to a lower cooperativity of the transition. In contrast to poly(l-ornithine), (Orn)n, the c.d. spectrum of (Me3Orn)n remains almost unchanged after adding anionic surfactants such as sodium octyl sulphate (SOS) or sodium dodecyl sulphate (SDS). In organic solvents like methanol or isopropanol, in contrast to (Orn)a and (Lys)n, no α-helix formation occurs. However, in mixtures of these alcohols or dioxane with water, α-helix formation is induced by perchlorate, as in pure water. The thermal stability of the α-helix in these systems is increased. 相似文献
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Richard B. Silverman Mark A. Levy A.Jabbar Muztar James D. Hirsch 《Biochemical and biophysical research communications》1981,102(1):520-523
Intraperitoneal injection into mice of varying concentrations of (S)-4-amino-5-fluoropentanoic acid ((S)-AFPA) produces a dose-dependent irreversible decrease in brain γ-aminobutyric acid-α-ketoglutaric acid aminotransferase (E.C. 2.6.1.19) activity. Concomitant with this inactivation is an increase in whole brain γ-aminobutyric acid (GABA) levels. Four hours after a dose of 100 mg/kg body weight of (S)-AFPA to mice, endogenous brain GABA concentrations increase to 16 times that of the untreated animals and the enzyme activity decreases to 20% that of the controls. The binding of (S)-AFPA to GABA receptors was more than three orders of magnitude poorer than for GABA itself. 相似文献
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William W.-C. Chan 《Biochemical and biophysical research communications》1983,116(1):297-302
L-leucinthiol (2-amino-4-methyl-1-pentanethiol) was designed as an inhibitor of leucine aminopeptidase by analogy with sulfhydryl inhibitors of other zinc-containing peptidases. It was synthesized from L-leucinol and shown to be a potent competitive inhibitor of the microsomal aminopeptidase from porcine kidney (Ki = 2.2 × 10?8M). The results suggest that the mechanism of aminopeptidase may be similar to that of other metalloproteases. 相似文献
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Richard B. Silverman A. Jabbar Muztar Mark A. Levy James D. Hirsch 《Life sciences》1983,32(24):2717-2723
The effects of intraperitoneal administration of (S)-4-amino-5-fluoropentanoic acid, a mechanism-based covalent inactivator of γ-aminobutyric acid transaminase (GABA-T), on whole brain GABA metabolism in mice were investigated. A dose-dependent and time-dependent irreversible inactivation of GABA-T was observed with a concomitant increase in whole brain GABA levels. The compound exhibited no nor time-dependent inhibition of glutamate decarboxylase (GAD), alanine transaminase, or aspartate transaminase (Asp-T). It was, however, a potent competitive reversible inhibitor of GAD and a weak competitive inhibitor of Asp-T. The chloro analogue, (S)-4-amino-5-chloropentanoic acid, was ineffective. 相似文献
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Anders Berg Kjell Carlström Jan-Åke Gustafsson Magnus Ingelman-Sundberg 《Biochemical and biophysical research communications》1975,66(4):1414-1423
The steroid 15β-hydroxylase system of was obtained in a cell-free preparation through sonication. The strictly NADPH-dependent 15β-hydroxylase activity, measured using progesterone as substrate, was inhibited by carbon monoxide, SKF 525-A, imidazole and metyrapone, indicating that the reaction is cytochrome P-450-dependent. A 40-fold purification of cytochrome P-450 in cell-free extracts was obtained by chromatography on DEAE-cellulose yielding a concentration of 0.32 nmoles of cytochrome P-450 per mg of protein. This partially purified cytochrome P-450 preparation catalyzed 15β- and 15α-hydroxylation of progesterone in the presence of NaIO4 or NaClO2 but not in the presence of NADPH or NADH. 相似文献
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4-Methyl-α-ethyl-tyramine and its 4, α-dimethyl analogue release 5-HT from human blood platelets . At lower concentrations they inhibit the uptake of 5-HT into platelets. Tricyclic antidepressant drugs do not block 5-HT release by these compounds. On removal of the depletor, platelets recover their ability to take up 5-HT; platelets preloaded with exogenous 5-HT lose the same proportion of amine as those containing only endogenous 5-HT. Tetrabenazine behaves similarly, but its actions are partial, whereas those of the tyramines are more complete. The temperature dependence of spontaneous and drug-induced 5-HT release has been measured. The results are discussed in terms of the action of these drugs and with special reference to the use of human blood platelet as a model of a 5-HT-containing nerve ending. 相似文献
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Ronald E. Law Ralph M. Sinibaldi Michael R. Cummings Adolph J. Ferro 《Biochemical and biophysical research communications》1976,73(3):600-606
5′-Methylthioadenosine (MTA) inhibits the incorporation of [3H] uridine into RNA in salivary glands of . This effect is not due to an inhibition of [3H] uridine uptake into the glands. The inhibition of RNA synthesis by MTA is concentration dependent and maximum inhibition is observed after 45 minutes of incubation in the presence of 1 mM MTA. Experiments utilizing α-amanitin suggest that the synthesis of heterogeneous RNA is completely inhibited. 相似文献