Thiosulfate-cytochrome c-551 reductase derived from has been highly purified. The enzyme reduces cytochrome in the presence of thiosulfate while cytochrome -555 of the organism is not reduced by the enzyme. Cytochrome -555 reacts with the enzyme at an appreciable rate only in the presence of cytochrome -551. However, the reduction rate of cytochrome -551 by the enzyme is greatly enhanced on addition of a catalytic amount of cytochrome -555. Therefore, cytochrome -555 seems to function as an effector on thiosulfate-cytochrome -551 reductase as well as it acts as the electron donor to the light-excited chlorobium chlorophylls. 相似文献
The cytokinin-active nucleoside 6-(4-hydroxy-3-methyl--2-butenylamino)-9-β--ribofuranosylpurine, i.e. ribosyl--zeatin, has been isolated from an hydrolysate of tRNA from . The identification of ribosyl--zeatin is based on biological activity, liquid chromatographic mobility and uv spectrum of the purified material as well as the mass spectrum and gas chromatographic mobility of its trimethylsilylated derivative. 相似文献
The possible modes of binding for , , , and to concanavalin A have been investigated using theoretical methods. All these sugars, except , reach the active site of concanavalin A with a highly restricted number of binding orientations. Present investigations suggest that the failure of to bind to concanavalin A is not so much due to steric factors as to repulsive electrostatic interactions. can bind to concanavalin A in one mode whereas the other sugars can bind in more than one mode. The high potency of over is mainly due to the possibility of hydrophobic interactions of the α-methoxy group with Leu(99) or Tyr(100) and also due to the possibility of formation of better and more hydrogen bonds with the protein. A comparison of these data with those for the d-glucopyranosides suggests that the change of the hydroxyl at the C-2 atom from equatorial to axial orientation increases the stereochemically allowed region as well as the possible binding modes. From these studies it is also suggested that the overall shape of the oligosaccharides rather than the terminal or internal mannose alone affects the binding potency of saccharides to concanavalin A. 相似文献
The synthesis and characterization of - and -3,4-bis(4-hydroxyphenyl)-2-hexene (- and -pseudo-DES) and of -3,4-bis(4-hydroxyphenyl)-2-hexen-1-ol (-1-hydroxypseudo-DES) are described. These compounds are useful as probes in the study of hormone action. 相似文献
Two compounds were isolated from female (Lepidoptera: Noctuidae) extracts and identified as -9-tetradecenal and -ll-hexadecenal. Together they elicit intense male . response in laboratory tests and have attracted males in the field. Although -ll-hexadecenal is an . sex pheromone, no evidence was obtained for -9-tetradecenal in . . 相似文献
The second of the two reaction steps involved in the metabolic transformation of (?)-nicotine to (?)-cotinine , the oxidation of the intermediate is mediated mainly, if not solely, by the enzyme aldehyde oxidase (EC 1.2.3.1). Of the molecular species that constitute , nicotine Δ1′(5′) iminium ion appears to serve as the substrate. The enzyme has a strong affinity for , as shown in a study on the inhibition of the oxidation of 3-(aminocarbonyl)-1-methylpyridinium chloride. This study gave a value of Ki = 6 μM; Km = 2 μM (pH 7.4). Mainly in view of this finding, “iminium oxidase” seems to be a more adequate name than “aldehyde oxidase” for this enzyme. 相似文献
Three analogs of somatostatin, [-Cys14] -, [Ala2, -Cys14] - and [-Trp8, -Cys14] - somatostatin, were synthesized by the solid phase method, characterized by several means, and tested for their effects on the release of insulin, glucagon, and growth hormone. The peptides sharply suppressed the release of growth hormone and glucagon , but had less effect on insulin secretion . These analogs, particularly [-Trp8, -Cys14] - somatostatin, could possibly be useful for the treatment of diabetes mellitus. 相似文献
A minicell-producing strain of carrying an F′ factor, KLF10-1, forms minicells that contain plasmid but not chromosomal DNA. These minicells were found to synthesize two polypeptides corresponding precisely to the β and β′ subunits of RNA polymerase in SDS-polyacrylamide gel electrophoresis. In contrast, minicells obtained from an isogenic strain carrying F13-1 do not synthesize these proteins under similar conditions. These results indicate that the structural genes for the β′ as well as β subunits of the polymerase are located on the chromosomal segment (78 to 81 min on the standard genetic map of ) carried by KLF10-1. 相似文献
The transducing phage λd, carrying a portion of the chromosome including , is derived from the heat-inducible, lysis-defective strain λy199, which has the and deletions. Cleavage of λy199 DNA by RI endonuclease, followed by agarose slab gel electrophoresis, results in bands corresponding to the known C, D, E, and F segments of λ, and a segment A′ (A plus B minus minus , the cleavage site between A and B being eliminated). Cleavage of λd DNA by RI yields the expected D, E, and F segments of λ and four other segments, termed 14-1 through 14-4, whose length is 17.5, 6.2, 3.0, and 2.0 kilobases, respectively, as determined by electron microscopy and corroborated by electrophoretic mobility. Heteroduplex analysis shows that the cluster is on the 14-1 segment. 相似文献
We wish to report here the syntheses of (5, 6)-5-hydroxy-, (5, 6)-5-hydroxy-, (5, 6)-5-hydroxy-, and (5, 6)-5-hydroxy-PGI1 and their methyl ester derivatives. Treatment of (5, 6)-5-epoxy- and (5, 6)-5-epoxy-PFG1α methyl esters with acid washed silica gel afforded (5, 6)-5-hydroxy- and (5, 6)-5-hydroxy-PGI1 methyl esters; correspondingly, silica promoted cyclization of (5, 6)-epoxy- and (5, 6)-5-epoxy- PGF1 methyl esters yielded (5, 6)-5-hydroxy- and (5, 6)-5-hydroxy- PGI1 methyl esters. Alternatively, the 5-hydroxyl group was introduced into the PGI1 skeleton reaction of the 5-mercuric halides with sodium borohydride in the presence of oxygen. Stereochemical assignments were based on their mode of synthesis and 1H nmr shift differences. 相似文献
The potencies of (?)--Δ9-THC, (+)--Δ9-THC, (+)--Δ9-THC, (?)--Δ8-THC and (+)--Δ8-THC were compared in several different species. (?)--Δ9-THC was 100 times more potent than (+)--Δ9-THC in depressing schedule-controlled responding in monkeys. The (+)- isomers were less effective than their corresponding (?)- isomers in the dog static-ataxia test, but potency ratios could not be determined due to a lack of dose-responsiveness of the (+)- isomers. However, it appeared that their potency differed by at least ten fold. The potency of (+)--Δ9-THC in the dog static-ataxia test was comparable to that of (+)--Δ9-THC. The hypothermia in mice produced by the (?) isomers of -Δ9-THC and -Δ8-THC were 9.1 and 30.4 times greater than that produced by their respective (+)-isomers. Also, the potency ratio of the (+)- and (?)--Δ9-THC was 5.6 as measured by depression of spontaneous activity in mice. The magnitude of the potency ratios of the THC stereo-isomers is dependent upon the species and the pharmacological test used. 相似文献
α-(1→2)--Fucosidase, β--galactosidase and galactose oxidase are sterically hindered by certain types of branching in the oligosaccharide chains. 1) β--Galactosidase will not cleave galactose when the penultimate sugar carries a sialic acid residue as in I. 2) Galactose Oxidase will not oxidize the galactose residue in trisaccharide I but will in II. Moreover, neither galactose nor -acetylgalactosamine, glycosidically bound as in III, is susceptible to oxidation with galactose oxidase until the α-(1→2) linkage between them is cleaved by . 3) α-(1→2)--Fucosidase action is inhibited by or galactosyl residue, as in III and IV. Removal of the terminal sugars makes the fucosyl residue susceptible to fucosidase action. 相似文献
Incubation of UDP-[14C]--acetylglucosamine with calf pancreas microsomes in the presence of Mn++ and potassium thiocyanate gave a labeled glycolipid, tentatively identified as 1-2-acetamido-2-deoxy--glucosyl 2-dolichyl pyrophosphate on the basis of cochromatography with synthetic 1-2-acetamido-2-deoxy-α--glucopyranosyl 2-dolichyl pyrophosphate, similar chemical and enzymic hydrolyses of the biosynthetic and synthetic compounds, and stimulation of the biosynthesis by addition to the incubation mixture o dolichyl phosphate or a crude lipid fraction extracted from microsomes. 相似文献
Both pairs of -ll-desoxy- and -13---15, 16-dihydroxyprostaglandins have been synthesized via 1,4-conjugate additions of an appropriately functionalized -vinyl cuprate to the requisite cyclopentenone. These prostaglandin analogs are considerably less potent than PGE2 as gastric secretion inhibitors or as bronchodilators. 相似文献
We have measured the cytochrome compositions of subfractions derived from appressed and non-appressed thylakoids by centrifugation and aqueous two-phase partition. Cytochrome -559 (HP) was not detectable in the fraction derived from non-appressed thylakoids. Cytochromes -563 and -559 (LP) were all evenly distributed throughout the thylakoid membrane. This distribution points to plastocyanin as a possible lateral shuttle of reducing equivalents between spatially separated photosystems.Cytochrome was accessible to externally added plastocyanin in the inside-out vesicles but not in vesicles of normal sidedness. This strongly supports a location at the inner side of the thylakoid membrane. Cytochrome -563 was slowly reduced by dithionite in vesicles with both normal and inside-out orientation suggesting a location within the membrane interior. 相似文献
The hydrolysis of (±)--3-bromo-1,2-epoxycyclohexane in the presence of rabbit liver microsomes was investigated, and found to yield, beside -3-bromocyclohexane--1,-2-diol, 2,3-epoxycyclohexanol. It was demonstrated that the latter compound was the only product of the enzymatic reaction, whereas the diol resulted from a non enzymatic hydration in the reaction medium. These data provide the first direct proof for a general base catalysis in the enzymatic epoxide hydration, previously hypothesized on the basis of several lines of indirect evidence, and disprove alternative mechanisms involving protonation of the oxirane oxygen. 相似文献
-9-tetradecen-l-ol acetate was isolated from both extracts of female abdominal tips and of filter paper exposed to female (Walker). It is the second sex stimulant isolated from this species and, in stimulatory bioassays, it is ca. 1/100, 000 as active as the stimulant isolated previously, -9, -12-tetradecadien-l-ol acetate. According to attractancy tests, the natural sex pheromone system of complex contains other components in addition to these 2 stimulants. 相似文献
Recently, 1-β--arabinofuranosylcytosine-5′-diphosphate--1,2-dipalmitin (VIa) was reported to inhibit the growth of L51784 cells in mice and of human colon carcinoma HCT-15 cells, also in mice. This paper describes the synthesis of a single diastereomer by conversion of 1-β--arabinofuranosylcytosine 5′-monophosphate (II) to the nucleoside 5′-phosphomorpholidate (III), followed by reaction with -α-dipalmitoylphosphatidic acid (IV) to give 1-β--arabinofuranosylcytosine-5′-diphosphate--1,2-dipalmitin (V) in good yield. The separation of the product is described and its characterization by chromatography, elemental analysis, and spectroscopic methods. The lipophilic nature of V renders it insoluble in aqueous media and a method of sample preparation utilizing sonication techniques is described which provides a clear solution suitable for biological evaluation. In addition, the ability of V to inhibit the growth of L1210 cells and of mouse myeloma MPC 11 cells is desscribed and compared with 1-β--arabinofuranosylcytosine (I) and other lipophilic prodrugs of I. 相似文献
We have measured the fluorescence decay of using the phase-modulation method, in several solvent systems and egg phosphatidylcholine vesicles. The decay is monoexponential in pure solvents (both polar and non-polar) of low viscosity. In polar viscous solvents or in non-polar solvents containing an added polar solute, the decay is heterogeneous and emission wavelength dependent. In such cases, dielectric relaxation and/or excited-state complexing give rise to a shift of the emission spectrum on the nanosecond time scale. Emission-wavelength-dependent decay was also observed when was bound to egg phosphatidylcholine vesicles. From these results as well as the position of the emission spectral maximum, we conclude that probes the ester-carbonyl region of the phospholipid acyl chains, where it undergoes an excited-state reaction. This result contradicts the often made assumption that probes the deeper hydrocarbon region of the bilayer. 相似文献
Acid-hydrolysis of the phospholipid fraction of and demonstrated the presence of two neutral lipid products. Characterization of these lipids resulted in their identification as dialkyl glyceryl ether and diglycerol tetraethers. The ether-linked alkyl chains were identified as the 20- and 40-carbon branched chains for the diether and tetraether, respectively. and were also characterized by the presence of acid-stable phospholipid components. 相似文献