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排序方式: 共有426条查询结果,搜索用时 31 毫秒
1.
2.
The amino acid sequence for the variant-3 (CsE-v3) toxin from the venom of the scorpion Centruroides sculpturatus Ewing contains eight aromatic residues. By use of 2D NMR spectroscopic methods, the resonances from the individual protons (NH, C alpha H, C beta H',H", and the ring) for each of the individual aromatic residues have been completely assigned. The spatial arrangement of the aromatic ring systems with respect to each other has been qualitatively analyzed by 2D-NOESY techniques. The results show that Trp-47, Tyr-4, and Tyr-42 are in close spatial proximity to each other. The NOESY contacts and the ring current induced shifts in the resonances of the individual protons of Tyr-4 and Trp-47 suggest that the aromatic ring planes of these residues are in an orthogonal arrangement. In addition, the spatial proximity of the rings in the pairs Tyr-4, Tyr-58; Tyr-42, Tyr-40; and Tyr-40, Tyr-38 has also been established. A comparison with the published crystal structure suggests that there is a minor rearrangement of the aromatic rings in the solution phase. No 2D-NOESY contacts involving Phe-44 and Tyr-14 to any other aromatic ring protons have been observed. The pH dependence of the aromatic ring proton chemical shifts has also been studied. These results suggest that the Tyr-58 phenolic group is experiencing a hydrogen-bonding interaction with a positively charged group, while Tyr-4, -14, -38, and -40 are experiencing through-space interactions with proximal negatively charged groups. The Trp-47 indole NH is interacting with the carboxylate groups of two proximal acidic residues. These studies define the microenvironment of the aromatic residues in the variant-3 neurotoxin in aqueous solution. 相似文献
3.
Synopsis Evidence is presented which suggests that the nonparasitic lamprey, Lampetra (Eudontomyzon) gracilis Kux, 1965, is conspecific with the parasitic lamprey Eudontomyzon danfordi Regan, 1911. The diagnostic characters of the holotype and of the non-type material of E. gracilis are features found in E. danfordi specimens in their second and final year of adult life, thereby making the former a junior synonym of the latter. 相似文献
4.
5.
1H NMR studies of lambda cro repressor. 1. Selective optimization of two-dimensional relayed coherence transfer spectroscopy 总被引:1,自引:0,他引:1
Two-dimensional relayed coherence transfer NMR spectroscopy (RELAY) has been used to corroborate side chain spin system identities in crowded regions of the 1H NMR spectrum of the lambda cro repressor protein. The mixing time in the RELAY experiments was optimized for specific preselected spin systems by using recently developed methods [Bax, A., & Drobny, G. (1985) J. Magn. Reson, 61, 306-320], which utilize the transverse relaxation time (T2) of the molecule and relevant J couplings for the defined spin system. We demonstrate that a mixing time of 26 ms gives rise to strong C alpha H-C gamma H3 RELAY cross peaks for all valine, threonine, and isoleucine residues, while RELAY cross peaks for other spin systems are weak or are not observed. This allows for rapid and unambiguous identification of the side chain resonances for valine, isoleucine, threonine, and alanine (by elimination). The use of optimized RELAY for analyzing and identifying spin systems in complex spectra is discussed. 相似文献
6.
Stefan Boehm Sigismund Huck Gabriele Koth Helmut Drobny Ernst Agneter Ernst A. Singer 《Journal of neurochemistry》1994,63(1):146-154
Abstract: This study explores the role of cyclic AMP in electrically evoked [3H]noradrenaline release and in the α2-adrenergic modulation of this release in chick sympathetic neurons. Along with an increase in stimulation-evoked tritium overflow, applications of forskolin enhanced the formation of intracellular cyclic AMP. Both effects of forskolin were potentiated by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. The forskolin-induced increase in overflow was abolished by the Rp-diastereomer of cyclic AMP-thioate, an antagonist at cyclic AMP-dependent protein kinases, and 1,9-dideoxy-forskolin, an inactive analogue at adenylyl cyclase, had no effect on the evoked overflow. A 24-h pretreatment with either cholera toxin or forskolin reduced the subsequent forskolin-induced accumulation of cyclic AMP and inhibited the stimulation-evoked release. Basal cyclic AMP production, however, remained unaltered after forskolin treatment and was enhanced after 24 h of cholera toxin exposure. The α2-adrenergic agonist bromoxidine did not affect the formation of cyclic AMP stimulated by forskolin but reduced electrically evoked release. However, effects of bromoxidine on 3H overflow were attenuated by forskolin as well as by 8-bromo-cyclic AMP. Effects of bromoxidine on [3H]noradrenaline release were paralleled by an inhibition of voltage-activated Ca2+ currents, primarily through a delayed time course of current activation. This effect was abolished when either forskolin or 8-bromo-cyclic AMP was included in the pipette solution. Both substances, however, failed to affect Ca2+ currents in the absence of bromoxidine. These results suggest that the signaling cascade of the α2-adrenergic inhibition of noradrenaline release involves voltage-activated Ca2+ channels but not cyclic AMP. Elevated levels of cyclic AMP, however, antagonize this α2-adrenergic reduction, apparently through a disinhibition of Ca2+ channels. 相似文献
7.
The genes of two variant glucoamylases (GLA1 and GLU1) ofSaccharomycopsis fibuligera were expressed inSaccharomyces cerevisiae, and biochemical properties of the secreted enzymes were compared. It was found that three amino acid alterations in the signal peptide and N-terminal regions of the variants had no effect on the levels of the secreted enzymes. Amino acid alterations in the C-terminal region of the mature proteins influenced their specific activity, substrate specificity, as well as temperature and pH optima. Because of the glycosylation heterogeneity, the glucoamylases of each gene variant were isolated and purified in two forms (A and B), which were essentially similar in catalytic and physicochemical properties but differed in their thermal stability and ability to renaturate after thermal denaturation. 相似文献
8.
Mechanisms of the reactions of representative dipeptides (Gly2, Gly-Ala), oligopeptides (Gly3, Gly4) and the polypeptide (poly-Gly)n) in solution and clay suspensions at 85 degrees C were investigated. The reaction products and their yields were analysed and determined by means of HPLC. Interestingly, hydrolysis, where water molecules act as the reactant, was not the main reaction, even for oligopeptides. Formation of cyclic dipeptides prevailed in the reactions of dimers as well as oligopeptides. The breakdown of oligopeptide molecules proceeded via an intramolecular cyclization reaction. For example, the reaction of Gly3 led to the formation of equal amounts of cyclic dipeptide, c(Gly)2 and Gly. The presence of clay (montmorillonite) significantly increased yields in the reactions of dipeptides but it did not have much effect on the reactions of oligopeptides. However, an opposite effect of clay, protection of poly(Gly)n against decomposition, was proven. 相似文献
9.
Jasna Puizina Hanna Weiss-Schneeweiss Andrea Pedrosa-Harand Juraj Kamenjarin Ivo Trinajstic Karel Riha Dieter Schweizer 《Génome》2003,46(6):1070-1076
Chromosome analysis of three different populations of Hyacinthella dalmatica (Lallem.) Trinajsti?, an endemic species of the coastal region of southeastern Europe, showed a unique chromosome number, 2n = 2x = 20, and bimodal karyotype with one large and nine smaller pairs of chromosomes. Staining with fluorochromes CMA3 (chromomycin A3) and DAPI (4,6-diamidino-2-phenylindole) revealed heterochromatic regions associated with NORs, centromeres, and several interstitial heterochromatic bands on the longest chromosome pair. Double-target FISH with two ribosomal DNA probes revealed one locus of 5S rRNA genes in the pericentromeric region of chromosome pair 3 and one locus of 18S-5.8S-26S rRNA genes on the short arm of chromosome pair 4 in all plants and populations analyzed. Southern hybridization analysis and FISH experiments demonstrated that the distal ends of H. dalmatica chromosomes contain the vertebrate telomere (5'-TTAGGG-3') repeat type rather than the Arabidopsis (5'-TTTAGGG-3') heptamer, and so suggest that this Asparagales species along with Aloe and Othocallis contains the vertebrate-type telomere repeat. 相似文献
10.
The peptide bond formation of alanine (ala), ala + glycine (gly), ala + diglycine (gly2), and ala + gly cyclic anhydride (cyc-gly2) in drying/wetting cycles at 80°C was studied. Silica, alumina, and representative smectites—montmorillonite and hectorite—were
used as catalysts, and the dependence of reaction yields on the available amount of water in the reaction systems was evaluated.
Silica and alumina catalyze the formation of oligopeptide mainly in temperature fluctuation experiments, whereas higher amounts
of water in the reaction system support clay-catalyzed reactions. Silica and alumina are much more efficient for amino acid
dimerization than clays. Whereas only 0.1% of ala oligomerized on hectorite and no reaction proceeded on montmorillonite,
about 0.9 and 3.8% alanine converted into its dimer and cyclic anhydride on silica and alumina, respectively. Clay minerals,
on the other hand, seem to more efficiently catalyze peptide chain elongation than amino acid dimerization. The reaction yields
of ala-gly-gly and gly-gly-ala from ala + gly2 and ala + cyc-gly2 reached about 0.3% on montmorillonite and 1.0% on hectorite. The possible mechanisms of these reactions and the relevance
of the results for prebiotic chemistry are discussed.
Received: 15 December 1996 / Accepted: 1 May 1997 相似文献