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91.
Spore germination in Dryopteris filix-mas occurs via a cascade of cellular responses, and chlorophyll formation, mitosis or rhizoid elongation are commonly used as parameters to determine spore germination. Detailed investigations of these parameters led to the hypothesis that they are regulated by different, independent phytochrome-mediated responses. This concept could be confirmed, as is described in this paper which demonstrates that perception of light via phytochrome occurs within two different phases separated in time. Presence of the far-red absorbing phytochrome form, Pfr, for 36 h, induces chlorophyll formation and the first unequal cell division, by which a rhizoid initial and a protonemal initial are formed (first phytochrome-mediated response). However, rhizoid elongation requires a second period of Pfr, presence (second phytochrome-mediated response). There is a clear temporal distinction between the first and the second phytochrome-mediated response with respect to the coupling of Pfr to the transduction chain; Pfr is unable to induce rhizoid growth until 60 h after the start of the first red irradiation. The effectivity of Pfr for inducing the second response shows an optimum at ca 96 h after the beginning of the presence of Pfr; thereafter, it declines slowly. The fluence-response relationship and the presence of red/far-red reversibility demonstrate that rhizoid elongation is a low-fluence response mediated by phytochrome and is independent of the first phytochrome response. 相似文献
92.
Bernd Sauerbrei Jutta Niggemann Stefan Gröger Sungsook Lee Heinz G. Floss 《Carbohydrate research》1996,280(2):223-235
To prepare labeled precursors for biosynthetic studies, methods for the specific introduction of tritium and deuterium into the reducing and the terminal glucose unit of maltotriose were developed. Thus [6″-3H]- and (6″-2H)-maltotriose (17) and (18) were prepared via selective methoxytritylation, deprotection and subsequent modified Pfitzner-Moffatt oxidation, followed by reduction with sodium borotritiide or sodium borodeuteride, respectively. A simple two step procedure utilizing the Lobry de Bruyn/van Ekenstein transformation gave (2-2H)maltotriose (20). 相似文献
93.
Stefan Vielhauer Anne Rudolphi Karl-Siegfried Boos Dietrich Seidel 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1995,666(2)
A fully automated coupled-column HPLC method for on-line sample processing and determination of the photoreactive drug 8-methoxypsoralen (8-MOP) in plasma has been developed. The method is based on the novel internal-surface reversed-phase precolumn packing materials Alkyl-Diol Silica (ADS). This new family of restricted-access materials has a hydrophilic, electroneutral outer particle surface and a hydrophobic internal pore surface. The supports tolerate the direct and repetitive injection of proteinaceous fluids such as plasma and allow a classical C18-, C8- or C4-reversed-phase partitioning at the internal (pore) surface. The total protein load, i.e. the lifetime of the precolumn used in this study (C8-Alkyl-Diol Silica, 25 μm, 25 × 4 mm I.D.), exceeds more than 100 ml of plasma. 8-MOP was detected by its native fluorescence (excitation 312 nm, emission 540 nm). Validation of the method revealed a quantitative and matrix-independent recovery (99.5–101.3% measured at five concentrations between 21.3 and 625.2 ng of 8-MOP per milliliter of plasma), linearity over a wide range of 8-MOP concentrations (1.2–3070 ng of 8-MOP/ml, r = 0.999), low limits of detection (0.39 ng of 8-MOP/ml) and quantitation (0.79 ng of 8-MOP/ml) and a high between-run (C.V. 1.47%, n = 10) and within-run (C.V. 1.33%, n = 10) reproductivity. This paper introduces coupled-column HPLC as a suitable method for on-site analysis of drug plasma profiles (bedside-monitoring). 相似文献
94.
The fluorescence characteristics of ethidium bromide (Eb) complexed to calf thymus DNA have been examined using fluorescence lifetime analysis for a range of DNA (effective nucleotide concentration) to Eb molar ratios. Control of both temperature and ion concentration is necessary for reproducible analyses. Eb complexed to double stranded DNA has a maximum fluorescence lifetime of 23 ns and is easily distinguishable from a fluorescence lifetime value of 1.67 ns corresponding to unbound Eb. In a solution of calf thymus DNA containing excess Eb a binding equilibrium is reached, and this corresponds to one Eb molecule for every five nucleotides. With increasing amounts of unbound Eb, the fluorescence lifetime of the DNA-Eb complex decreases with a concomitant drop in the steady state fluorescence intensity, without a change in the amount of Eb bound to DNA. It is concluded that unbound Eb, acting via a quenching mechanism, shortens the fluorescence lifetime of bound Eb and consequently decreases the overall fluorescence intensity. This means that a different approach is necessary: time-resolved fluorescence spectroscopy directly distinguishes between a decrease in fluorescence intensity due to quenching by an excess of unbound Eb from that due to a decrease in Eb binding to double-stranded DNA. These studies suggest that techniques which measure total steady state fluorescence intensity of bound Eb in order to infer relative amounts of double-stranded DNA must be interpreted with caution. For such assays to be valid it is essential that no unbound Eb be present; otherwise a variable correction factor is required to account for unbound Eb. 相似文献
95.
Genetic and environmental correlations among serum lipids and apolipoproteins in elderly twins reared together and apart. 总被引:4,自引:0,他引:4 下载免费PDF全文
D. A. Heller N. L. Pedersen U. de Faire G. E. McClearn 《American journal of human genetics》1994,55(6):1255-1267
Genetic and environmental correlations among five serum-lipid measures were examined in the Swedish Adoption/Twin Study of Aging. The sample included 302 twin pairs; 146 of these twin pairs were separated at an early age and were reared apart. The lipid measures examined include total cholesterol, HDL-cholesterol, triglycerides, and apolipoproteins A-I and B. Genetic and environmental correlations were evaluated for two different age groups, formed by dividing the sample at the median. The younger group included individuals 41.8-65.4 years of age at the midpoint of testing, although only 24 individuals were < 50 years of age. The older group included all those > 65.4 years of age, up to age 87 years of age. Substantial genetic correlations were found within each age group, although there is no evidence for a single genetic factor common to all five lipids. The comparison of twins reared together with twins reared apart allowed estimation of the effects of shared rearing environment; however, shared rearing environment only appears to be a significant mediator of the phenotypic correlation between apolipoprotein B and cholesterol in the older group. Examination of the genetic and environmental covariances suggests that the relative contributions of genetic factors are lower in the older group. Nonshared environmental factors are relatively more important mediators of phenotypic correlations among the serum lipids in individuals > 65.4 years of age than they are for the younger group. Sex differences in the mediation of these serum lipids were not as clear. 相似文献
96.
Metabolism of Pyrene by the Basidiomycete Crinipellis stipitaria and Identification of Pyrenequinones and Their Hydroxylated Precursors in Strain JK375 总被引:2,自引:2,他引:0 下载免费PDF全文
The metabolism of pyrene, a polycyclic aromatic hydrocarbon, by submerged cultures of the basidiomycete Crinipellis stipitaria was studied. After incubation for 68 h at 25°C in a 20-liter fermentor with complex medium and 20 mg of pyrene per liter, five metabolites were detected. The compounds were isolated by preparative high-performance liquid chromatography on RP18 and DIOL gels. By UV, infrared, and 1H nuclear magnetic resonance spectroscopy and mass spectrometry, 1-hydroxypyrene, 1,6-dihydroxypyrene, 1,8-dihydroxypyrene, 1,6-pyrenequinone, and 1,8-pyrenequinone were identified. 1,6- and 1,8-dihydroxypyrene were obtained from fungal cultures for the first time. The formation of these metabolites was confirmed by investigations with [4,5,9,10-14C]pyrene. 相似文献
97.
Richard W. Hyman Susan Frank Craig H. Warden Aaron Daluiski Renu Heller Aldons J. Lusis 《Biochemical genetics》1994,32(11-12):397-407
Quantitative trait locus (QTL) analysis is a statistical method that can be applied to identify loci making a significant impact on a phenotype. For the phenotype of susceptibility to diet-induced atherosclerosis in the mouse, we have studied four quantitative traits: area of aortic fatty streaks and serum concentrations of high-density lipoprotein-bound cholesterol (HDL-cholesterol), apolipoprotein A-I, and apolipoprotein A-II (apo A-II). QTL analysis revealed a significant locus on chromosome 1 distal impacting serum apo A-II concentration on a high-fat diet and serum HDL-cholesterol concentration on a chow diet. This locus is presumablyApoa-2, the structural gene for apo A-II. QTL analysis of aortic fatty streaks failed to reveal a significant locus. 相似文献
98.
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
99.
100.
Pool sequencing of natural HLA-DR,DQ, and DP ligands reveals detailed peptide motifs,constraints of processing,and general rules 总被引:6,自引:6,他引:0
Kirsten Falk Olaf Rötzschke Stefan Stevanovíc Günther Jung Hans-Georg Rammensee 《Immunogenetics》1994,39(4):230-242
We have approached the problem of MHC class II ligand motifs by pool sequencing natural peptides eluted from HLA-DR, DQ, and DP molecules. The results indicate surprisingly clear patterns, although not quite as clear as with natural class I ligands. The most striking feature is a highly dominant Proline at position 2. We interpret this to be a consequence of aminopeptidase N-like activity in processing. Another general aspect is the existence of three to four hydrophobic or aromatic anchors, whereby the first and the last are separated by five to eight residues. The peptide motifs for HLA-DR1, DR5, DQ7, and DPw4 are allele-specific and differ by spacing and occupancy of anchors. The anchors tend to be flanked by clusters of charged residues, and small residues, especially Ala, are frequent in the motif centers. These detailed motifs allow one to interpret most previous (DR-) motifs as fitting one or more of the anchors or conserved clusters. The relative motif symmetry suggests the possibility of bidirectional binding of peptides in the class II groove. 相似文献