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991.
Shinichi Kitamura Takashi Hirano Kenichi Takeo Mitsuru Mimura Kanji Kajiwara Bjrn T. Stokke Tsutomu Harada 《International journal of biological macromolecules》1994,16(6)
The conformation and dilute solution properties of (2→1)-β-d-fructan in aqueous solution were studied by gel permeation chromatography, low-angle laser light-scattering photometry, viscometry, small-angle X-ray scattering and electron microscopy. Fractions covering a broad range of weight-average molecular weights (Mw) from 1.49 × 104 to 5.29 × 106 were obtained from a native sample by ultrasonic degradation and fractional precipitation. For Mw < 4 × 104, the intrinsic viscosity [η] varies with Mw0.71, indicating that the fructan chain behaves as a random coil expanded by an excluded-volume effect in this molecular weight region. For Mw > 105, [η] exhibits an unusually weak dependence on Mw and finally becomes almost independent of molecular weight. This behaviour is interpreted in terms of a globular conformation of the high-molecular-weight fructan molecules. Small-angle X-ray-scattering measurements and electron microscopic observations support this interpretation of the values of [η] observed. 相似文献
992.
Selenite has been shown to undergo intracellular metabolism that results in its conversion to other low molecular weight Secontaining
species and also to its incorporation into a selenocysteine residue in selenoprotein. In order to investigate whether the
incorporation into protein is required for the cytotoxic effects of selenite, we have examined whether inhibition of protein
synthesis prevents the inhibitory effect of selenite on the ability of cells to form colonies or to synthesize RNA. We have
found that treatment of HeLa cells with cycloheximide inhibited protein synthesis by >90% but had no effect on the inhibitory
effect of selenite on cell colony formation or RNA synthesis. Since protein synthesis is not necessary for these cytotoxic
effects of selenite they are unlikely to result from an increase in the synthesis of selenoproteins. 相似文献
993.
José Antonio Jarillo Juan Capel Antonio Leyva José Miguel Martínez-Zapater Julio Salinas 《Plant molecular biology》1994,25(4):693-704
We have isolated two Rare Cold-Inducible (RCI1 and RCI2) cDNAs by screening a cDNA library prepared from cold-acclimated etiolated seedlings of Arabidopsis thaliana with a subtracted probe. RNA-blot hybridizations revealed that the expression of both RCI1 and RCI2 genes is induced by low temperature independently of the plant organ or the developmental stage considered. However, RCI1 mRNA accumulates faster and at higher levels than the RCI2 one indicating that these genes have differential responsiveness to cold stress. Additionally, when plants are returned to room temperature, RCI1 mRNA decreases faster than RCI2. In contrast to most of the cold-inducible plant genes characterized, the expression of RCI1 and RCI2 is not induced by ABA or water stress. The nucleotide sequences of RCI1 and RCI2 cDNAs predict two acidic polypeptides of 255 and 251 amino acids with molecular weights of 29 and 28 kDa respectively. The alignment of these polypeptides indicates that they have 181 identical amino acids suggesting that the corresponding genes have a common origin. Sequence comparisons reveal no similarities between the RCI proteins and any other cold-regulated plant protein so far described. Instead, they demonstrate that the RCI proteins are highly homologous to a family of proteins, known as 14-3-3 proteins, which are thought to be involved in the regulation of multifunctional protein kinases. 相似文献
994.
Hanns Ulrich Seitz Dorothea Elisabeth Gärtner 《Plant Cell, Tissue and Organ Culture》1994,38(2-3):337-344
In contrast to undifferentiated cell suspension cultures of Digitalis lanata, photomixotrophic shoot cultures of Digitalis purpurea accumulate cardiac glycosides in substantial concentrations. They are used to investigate enzymes of the cardenolide pathway. All cardenolides are 5-configurated. The progesterone 5-reductase and the 3-hydroxysteroid-5-oxidoreductase are present in shoot cultures but not in undifferentiated cell cultures. These enzymes provide precursors for cardenolides, whereas the presence of the progesterone 5-reductase, also present in shoot cultures, is discussed with regard to its role in phytosterol biosynthesis and may be attributed to the general steroid pathway. The progesterone 5-reductase had an activity maximum during the early growth period seven days after onset of cultivation, whereas the corresponding progesterone 5-reductase activity was highest on day 11. The maximum cardenolide accumulation was after 24 days. The enzyme activities present in crude extracts from shoot cultures were characterized with regard to their requirements for NADPH and NADH, pH-optimum, temperature optimum, affinity to their substrates and their localization in the cell. The progesterone 5-reductase was purified 769-fold.Abbreviations DW
dry weight
- FW
fresh weight
- PVP
polyvinylpyrrolidone 相似文献
995.
996.
Gregory A. Ordway Peter S. Widdowson Karen Streator Smith Angelos Halaris 《Journal of neurochemistry》1994,63(2):617-624
Abstract: The binding of an agonist, p-[125I]iodoclonidine, and an antagonist, [3H]yohimbine, to α2-adrenoceptors was measured autoradiographically in the locus coeruleus from 10 pairs of antidepressant-free victims of suicide and age-matched controls. Agonist binding to α2-adrenoceptors was significantly greater in the locus coeruleus from victims of suicide compared with control subjects. In contrast, antagonist binding to α2-adrenoceptors in the locus coeruleus did not differ significantly between control and suicide subjects. HPLC analysis of norepinephrine in tissue sections of the locus coeruleus did not reveal any differences between control subjects and suicide victims, suggesting that differences in agonist binding are not a result of differences in retention of the endogenous agonist norepinephrine in tissue sections. The increase in agonist binding to α2-adrenoceptors in the locus coeruleus of victims of suicide links an altered expression of the high-affinity state of autoinhibitory α2-adrenoceptors with suicide. 相似文献
997.
Abstract: cis -Methyldioxolane (CD) is a muscarinic receptor agonist. [3 H] CD has been used to label a subpopulation of muscarinic receptors described as exhibiting high agonist affinity. Pharmacological evidence suggests that the population of receptors labeled by [3 H] CD consists of m2 and/or m4 subtypes; however, no studies have directly addressed the subtype selectivity of [3 H] CD. The present study characterizes binding of this ligand to individual human receptor subtypes expressed in transfected Chinese hamster ovary cells. Results indicate that [3 H] CD binds with high affinity only to Hm2 receptors but not to all Hm2 receptors. Twenty-eight percent of Hm2 receptors bound [3 H] CD with a K D of 3.5 ± 0.5 nM. Binding was eliminated in the presence of guanosine 5'- O -(3-thiotriphosphate), indicating that the Hm2 receptors labeled by [3 H] CD are those that are associated with GDP-bound G protein. Binding of [3 H] CD by only a subpopulation of Hm2 receptors is in agreement with data generated from studies of [3 H] CD binding in mammalian brain. Because muscarinic receptors have been implicated to play a role in the pathogenesis of both Alzheimer's and Parkinson's disease, as well as the neurotoxicity of organophosphorus compounds, knowledge of the binding specificity of the muscarinic agonist [3 H] CD should aid research in these areas. 相似文献
998.
Ian J. Reynolds 《Journal of neurochemistry》1994,62(1):54-62
Abstract: This study investigated the binding of [3H] CGP 39653, a novel high-affinity antagonist of the N-methyl-D- aspartate (NMDA) recognition site of the NMDA receptor complex. [3H] CGP 39653 bound to the NMDA receptor in well washed rat brain membranes with an affinity of about 15 nM. Other NMDA site drugs inhibited [3H] CGP 39653 binding with the following order of potency: DL-(tetrazol-5- yl)glycine > glutamate > CGS 19755 > DL-2-amino-5- phosphonovalerate (DL-AP5) > NMDA. Glycine and 5, 7- dichlorokynurenate partially inhibited binding. The poly-amines spermine and spermidine increased [3H] CGP 39653 binding (EC50 values of 10 and 22 μM, respectively). This effect was mimicked by arcaine, 1, 5-diethylaminopiperidine, diaminodecane, diethylenetriamine, and Mg2+. The increase in [3H] CGP 39653 was a result of an increased affinity of the binding site for the ligand with very little effect on binding site density. Spermine and Mg2+also increased the affinity of the antagonists DL-AP5 and CGS 19755, but had only minor effects on the affinity of glutamate and NMDA. Arcaine did not reverse the enhancement of [3H] CGP 39653 binding by spermine, spermidine, or Mg2+. Channel-blocking dissociative anesthetics, including dizocilpine and ketamine, did not alter basal or Mg2+-stimulated [3H] CGP 39653 binding. Spermine did not alter either the enhancement of [3H]- dizocilpine by glutamate or the inhibition of [3H]dizocilpine by DL-AP5 or CGS 19755. These studies show that poly-amines and divalent cations selectively enhance the affinity of antagonists for the agonist binding site on the NMDA receptor complex. However, this effect is mediated by a site independent of the primary polyamine site defined using [3H] dizocilpine binding. 相似文献
999.
Susan J. Vannucci 《Journal of neurochemistry》1994,62(1):240-246
Abstract: Two glucose transport proteins, GLUT1 and GLUT3, have been detected in brain. GLUT1 is concentrated in the endothelial cells of the blood-brain barrier and may be present in neurons and glia; GLUT3 is probably the major neuronal glucose transporter. Of the few studies of glucose transport in the immature brain, none has quantified GLUTS. This study used membrane isolation and immunoblotting techniques to examine the developmental expression of GLUT1 and GLUT3 in four forebrain regions, cerebral microvessels, and choroid plexus, from rats 1–30 days postnatally as compared with adults. The GLUT1 level in whole brain samples was low for 14 days, doubled by 21 days, and doubled again to attain adult levels by 30 days; there was no regional variation. The GLUT3 level in these samples was low during the first postnatal week, increased steadily to adult levels by 21–30 days, and demonstrated regional specificity. The concentration of GLUT1 in microvessels increased steadily after the first postnatal week; the GLUT1 level in choroid plexus was high at birth, decreased at 1 week, and then returned to near fetal levels. GLUT3 was not found in microvessels or choroid plexus. This study indicates that both GLUT1 and GLUT3 are developmentally regulated in rat brain: GLUT1 appears to relate to the nutrient supply and overall growth of the brain, whereas GLUT3 more closely relates to functional activity and neuronal maturation. 相似文献
1000.
Abstract: In a previous study, protein kinase FA /glycogen synthase kinase-3 ( FA /GSK-3 ) was identified as a myelin basic protein (MBP) kinase associated with intact brain myelin. In this report, the phosphorylation sites of MBP by kinase FA /GSk-3 were further determined by two-dimensional electrophoresis/TLC, phosphoamino acid analysis, tryptic peptide mapping, Edman degradation, and direct sequencing. Kinase FA /GSK-3 phosphorylates MBP on both threonine and serine residues. Three tryptic phosphopeptide peaks were resolved by C18 reverse-phase HPLC. Sequential manual Edman degradation together with direct sequence analysis revealed that T(p)PPPSQGK is the phosphorylation site sequence for the first major phosphopeptide peak. When mapping with the bovine brain MBP sequence, we finally demonstrate Thr97 -Pro, one of the in vivo phosphorylation sites in MBP, as the major site phosphorylated by kinase FA /GSK-3, implicating a physiologically relevant role of FA /GSK-3 in the regulation of brain myelin function. By using the same approach, we also identified NIVT94 (p)PR as the phosphorylation site sequence in the second major tryptic phosphopeptide derived from [32 P]MBP phosphorylated by kinase FA /GSK-3, further indicating that kinase FA /GSK-3 represents a Thr-Pro motif-directed MBP kinase involved in the phosphorylation of brain myelin. 相似文献