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991.
G. M. Budd J. R. Brotherhood D. W. Thomas F. A. Beasley A. L. Hendrie S. E. Jeffery G. J. Lincoln A. T. Solaga 《European journal of applied physiology and occupational physiology》1993,67(5):450-456
The purpose of this study was to see whether artificial acclimatization to cold would reduce the pressor response to noradrenaline (NA) as natural acclimatization has been shown to do, and whether it would induce nonshivering thermogenesis. Three white men were infused with NA at four dosage levels between 0.038 and 0.300 g·kg–1·min–1 (2–23 g·min–1), before and after artificial acclimatization to cold and again 4 months later when acclimatization had decayed. Acclimatization was induced by ten daily cold (15°Q baths of 30–60 min followed by rapid rewarming in hot (38–42°C) water, and was confirmed by tests of the subjects responses to whole-body cooling in air. Three control subjects also underwent the first and third tests. Acclimatization substantially reduced the pressor response to NA at 0.150 and 0.300 g·kg–1·min–1, confirming earlier findings by the same technique in naturally acclimatized men, and its decay increased this response to beyond its initial levels (P<0.05 for both changes). Acclimatization did not change the response to NA of heart rate, subjective impressions, skin temperature of finger and toe, pulmonary ventilation, or plasma free fatty acids and ketone bodies. At no time did NA increase oxygen consumption, or increase skin temperature or heat flow over reported sites of brown fat. These findings would seem to show that acclimatization to cold reduces sensitivity to the pressor effect of NA but does not induce nonshivering thermogenesis, and that the reduced sensitivity is replaced by a hypersensitivity to NA when acclimatization decays. 相似文献
992.
Cholinesterases present homologies with some cell adhesion molecules; however, it is unclear whether and how they perform adhesive functions. Here, we provide the first direct evidence showing that neurite growth in vitro from various neuronal tissues of the chick embryo can be modified by some, but not all, anticholinesterase agents. By quantifying the neuritic G4 antigen in tectal cell cultures, the effect of anticholinesterases on neurite growth is directly compared with their cholinesterase inhibitory action. BW 284C51 and ethopropazine, inhibiting acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), respectively, strongly decrease neurite growth in a dose-dependent manner. However, echothiophate which inhibits both cholinesterases, does not change neuritic growth. These quantitative data are supplemented by morphological observations in retinal explant cultures grown on striped laminin carpets, viz., defasciculation of neurite bundles by BW 284C51 and Bambuterol occurs, indicating that these drugs disturb adhesive mechanisms. These data strongly suggest that a) cholinesterases can participate in regulating axonal growth, b) both AChE and BChE can perform such a nonsynaptic function, and c) this function is not the result of the enzyme activity per se, since at least one drug was found that inhibits all cholinesterase activities but not neurite growth. Thus, a secondary site on cholinesterase molecules must be responsible for adhesive functions. 相似文献
993.
Salt tolerance and methionine biosynthesis in Saccharomyces cerevisiae involve a putative phosphatase gene. 总被引:10,自引:0,他引:10 下载免费PDF全文
H U Glser D Thomas R Gaxiola F Montrichard Y Surdin-Kerjan R Serrano 《The EMBO journal》1993,12(8):3105-3110
The progressive salinization of irrigated land poses a threat to the future of agriculture in arid regions. The identification of crucial metabolic steps in salt tolerance is important for the understanding of stress physiology and may provide the tools for its genetic engineering. In the yeast Saccharomyces cerevisiae we have isolated a gene, HAL2, which upon increase in gene dosage improves growth under NaCl and LiCl stresses. The HAL2 protein is homologous to inositol phosphatases, enzymes known to be inhibited by lithium salts. Complementation analysis demonstrated that HAL2 is identical to MET22, a gene involved in methionine biosynthesis. Accordingly, methionine supplementation improves the tolerance of yeast to NaCl and LiCl. These results demonstrate an unsuspected interplay between methionine biosynthesis and salt tolerance. 相似文献
994.
Simon Y. C. Wong Geoffrey R. Guile Thomas W. Rademacher Raymond A. Dwek 《Glycoconjugate journal》1993,10(3):227-234
Glycopeptides can be valuable tools in determining the influence of carbohydrate moieties on the intrinsic properties of glycoproteins. However, glycopeptides of sufficient quantity and purity are as yet not readily available from biological sources. The chemical coupling of a -glycosylamino group of an unprotected carbohydrate with an activated aspartic acid residue of an unprotected peptide is a simple method for synthesizing asparagine-linked glycopeptides. In this report we demonstrate that the use of this method is not restricted to -glycosylamines of simple monosaccharides or short aspartic acid-containing pentapeptides. This is illustrated by the syntheses of several glycopentapeptides containingN,N-diacetylchitobiose, a glutamine-linked glycopentapeptide containing a biantennary complex oligosaccharide, and glycosylated variants of two analogs of a polypeptide hormone, atriopeptin, containingN,N-diacetylchitobiose.Abbreviations Ac
acetyl
- Bzl
benzyl
- DMF
dimethylformamide
- Fmoc
9-fluorenylmethoxycarbonyl
- Fuc
fucose
- Gal
galactose
- GlcNAc
N-acetylglucosamine
- HBTU
O-benzotriazol-1-yl-N,N,N,N-tetramethyluroniumhexa-fluorophosphate
- HOBt
1-hydroxybenzotriazole
- Man
mannose
-
m/z
mass/charge
- NMR
nuclear magnetic resonance
- Xyl
xylose
- Z
benzyloxycarbonyl; unless otherwise specified, amino acids are abbreviated using their one-letter codes. 相似文献
995.
The hyperthermophilic archaeon Pyrococcus furiosus was grown on pyruvate as carbon and energy source. The enzymes involved in gluconeogenesis were investigated. The following findings indicate that glucose-6-phosphate formation from pyruvate involves phosphoenolpyruvate synthetase, enzymes of the Embden-Meyerhof pathway and fructose-1,6-bisphosphate phosphatase.Cell extracts of pyruvate-grown P.furiosus contained the following enzyme activities: phosphoenolpyruvate synthetase (0.025 U/mg, 50 °C), enolase (0.9 U/mg, 80 °C), phosphoglycerate mutase (0.13 U/mg, 55 °C), phosphoglycerate kinase (0.01 U/mg, 50 °C), glyceraldehyde-3-phosphate dehydrogenase reducing either NADP+ or NAD+ (NADP+: 0.019 U/mg, NAD+: 0.009 U/mg; 50 °C), triosephosphate isomerase (1.4 U/mg, 50 °C), fructose-1,6-bisphosphate aldolase (0.0045 U/mg, 55 °C), fructose-1,6-bisphosphate phosphatase (0.026 U/mg, 75 °C), and glucose-6-phosphate isomerase (0.22 U/mg, 50 °C). Kinetic properties (V
max values and apparent K
m values) of the enzymes indicate that they operate in the direction of sugar synthesis. The specific enzyme activities of phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase (NADP+-reducing) and fructose-1,6-bisphosphate phosphatase in pyruvate-grown P. furiosus were by a factor of 3, 10 and 4, respectively, higher as compared to maltose-grown cells suggesting that these enzymes are induced under conditions of gluconeogenesis. Furthermore, cell extracts contained ferredoxin: NADP+ oxidoreductase (0.023 U/mg, 60 °C); phosphoenolpyruvate carboxylase (0.018 U/mg, 50 °C) acts as an anaplerotic enzyme.Thus, in P. furiosus sugar formation from pyruvate involves reactions of the Embden-Meyerhof pathway, whereas sugar degradation to pyruvate proceeds via a modified non-phosphorylated Entner-Doudoroff pathway. 相似文献
996.
Demonstration of Z-d(5BrCGAT5BrCG) and B-d(CGCGATCGCG) form crystal structures in DNA-cobalt hexammine complexes by Kr 647.1 nm excitation of Raman spectra. 下载免费PDF全文
Cobalt hexammine [Co(NH3)6(3+)] is an efficient DNA complexing agent which significantly perturbs nucleic acid secondary structure. We have employed red excitation (647.1 nm) from a krypton laser to obtain Raman spectra of the highly colored complexes formed between cobalt hexammine and crystals of the DNA oligomers, d(5BrCGAT5BrCG) and d(CGCGATCGCG), both of which incorporate out-of-alternation pyrimidine/purine sequences. The Co(NH3)6(3+) complex of d(5BrCGAT5BrCG) exhibits a typical Z-form Raman signature, similar to that reported previously for the alternating d(CGCGCG) sequence. Comparison of the Raman bands of d(5BrCGAT5BrCG) with those of other oligonucleotide and polynucleotide structures suggests that C3'-endo/syn and C3'-endo/anti thymidines may exhibit distinctive nucleoside conformation markers, and tentative assignments are proposed. The Raman markers for C2'-endo/anti adenosine in this Z-DNA are consistent with those reported previously for B-DNA crystals containing C2'-endo/anti dA. Raman bands of the cobalt hexammine complex of d(CGCGATCGCG) are those of B-DNA, but with significant differences from the previously characterized B-DNA dodecamer, d(CGCAAATTTGCG). The observed differences suggest an unusual deoxyguanosine conformer, possibly related to a previously characterized structural intermediate in the B-->Z transition. The present results show that crystallization of d(CGCGATCGCG) in the presence of cobalt hexammine is not alone sufficient to induce the left-handed Z-DNA conformation. This investigation represents the first application of off-resonance Raman spectroscopy for characterization of highly chromophoric DNA and illustrates the feasibility of the Raman method for investigating other structurally perturbed states of DNA-cobalt hexammine complexes. 相似文献
997.
We investigate spike initiation and propagation in a model axon that has a slow regenerative conductance as well as the usual Hodgkin-Huxley type sodium and potassium conductances. We study the role of slow conductance in producing repetitive firing, compute the dispersion relation for an axon with an additional slow conductance, and show that under appropriate conditions such an axon can produce a traveling zone of secondary spike initiation. This study illustrates some of the complex dynamics shown by excitable membranes with fast and slow conductances. 相似文献
998.
Susanne Popp Anna Jauch Detlev Schindler Michael R. Speicher Christoph Lengauer Helen Donis-Keller Harold C. Riethman Thomas Cremer 《Human genetics》1993,92(6):527-532
The identification of marker chromosomes in clinical and tumor cytogenetics by chromosome banding analysis can create problems. In this study, we present a strategy to define minute chromosomal rearrangements by multicolor fluorescence in situ hybridization (FISH) with whole chromosome painting probes derived from chromosome-specific DNA libraries and Alu-polymerase chain reaction (PCR) products of various region-specific yeast artificial chromosome (YAC) clones. To demonstrate the usefulness of this strategy for the characterization of chromosome rearrangements unidentifiable by banding techniques, an 8p+ marker chromosome with two extra bands present in the karyotype of a child with multiple anomalies, malformations, and severe mental retardation was investigated. A series of seven-color FISH experiments with sets of fluorochrome-labeled DNA library probes from flow-sorted chromosomes demonstrated that the additional segment on 8p+ was derived from chromosome 6. For a more detailed characterization of the marker chromosome, three-color FISH experiments with library probes specific to chromosomes 6 and 8 were performed in combination with newly established telomeric and subtelomeric YAC clones from 6q25, 6p23, and 8p23. These experiments demonstrated a trisomy 6pter6p22 and a monosomy 8pter8p23 in the patient. The present limitations for a broad application of this strategy and its possible improvements are discussed.Dedicated to Professor Dr. U. Wolf on the occasion of his 60th birthday 相似文献
999.
Andrew R. J. Curtis Sophie Headland Susan Lindsay Nicholas S. T. Thomas Eileen Boye Smaragda Kamakari Paul Roustan Maria Anvret Jan Wahlstrom Gillian McCarthy Angus J. Clarke Shomi Bhattacharya 《Human genetics》1993,90(5):551-555
Four families, each with two individuals affectecd by Rett Syndrome (RS), were analysed using restriction fragment lenght polymorphisms and microsatellite markers from the X chromosome. In two of the families, X-linked dominant inheritance of the RS defect from a germinally mosaic mother could be assumed. Therefore, maternal X chromosome markers showing discordant inheritance were used to exclude regions of the X chromosome as locations of the RS gene. Much of the short arm could be excluded, including regions containing three candidate genes, OTC, synapsin 1 and synaptophysin. Although most of the long arm was inherited in common it was possible to exclude a centromeric region. Inheritance of X chromosome markers is also presented for two families with affected aunt-niece pairs, one of which has not been previously studied at the DNA level. 相似文献
1000.
G. E. Davies C. M. Howard L. M. Gorman M. J. Farrer A. J. Holland R. Williamson A. M. Kessling 《Human genetics》1993,90(5):521-525
The COL6A1 and COL6A2 (collagen VI) gene cluster on chromosome 21 is a candidate region for defects leading to congenital heart anomalies in Down's syndrome. We report a variable number of tandem repeats (VNTR) and a restriction fragment length polymorphism (RFLP) in this gene region, detected using a COL6A1 cDNA probe. Linkage disequilibrium relationships were studied among the RFLPs of this gene cluster. The RFLP reported here shows no significant linkage disequilibrium with any others in the region. It has a polymorphism information content value of 0.27, raising the informativity of the locus. 相似文献