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- Chen, Zheng-wang
(författare)
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Isolation and characterization of novel intestinal polypeptides of the enteroinsular and brain-gut axes and of macrophages
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The gastrointestinal tract has been recognized as our largest endocrine organ, from which many peptide hormones, neuropeptides and growth factors have been isolated. There is also increasing evidence that the gastrointestinal tract can be considered as our largest immune organ, from which many antibacterial peptides, cytokines, cytotoxins and chemokines have been characterized. Different entero-endocrine cells, peptidergic nerve terminals and immune cells are found in this organ. This thesis describes the isolation and characterization, from intestinal tissues, of seven polypeptides, five porcine [daintain/AIF1, diazepam binding inhibitor (DBI), dopuin, pancreatic polypeptide (PP), vimentin-37] and two from chicken (DBI1-86 and DBI35-86). These peptides were first detected in chromatographic peptide fractions that influenced the glucose-induced secretion of insulin from rat, isolated pancreatic glands or islets. Purification was guided by monitoring this effect or chemically by analysis for the presence of cyst(e)ine peptides. The polypeptides dopuin (do, many; pu, proline) and daintain- /AIF1 (da, big; in, influencing; tai, peptide; in, insulin secretion /allograft inflammatory factor 1) represent novel structures. The multifunctional peptide DBI and the peptide hormone PP have now been isolated from intestinal tissues, while chicken DBI and its novel, processed form DBI35-86 represent peptides now isolated from avian sources. Both of the purified chicken DBI forms inhibit glucose-induced insulin release in vitro, and were not known in structure earlier. Dopuin is a 62-residue polypeptide with a high content of pro-line in its N-terminal part and a high proportion of histidine in its C-terminal part. Both proline and histidine are important residues for specific structures and specialized functions. Six half-cystine residues are present and shown to be involved in three intrachain di-sulphide bridges (Cys22-25, 23-54, 35-44) which contribute to a tightly folded core segment in the molecular structure. At 10 nM concentration, the peptide has an inhibitory tendency on glucose induced insulin release in vitro. Daintain/AIFI consists of 146 amino acid residues and is N-terminally acetyl blocked. An internal 44-residue segment with a sequence pattern (---KR--- KK---GKR---) resembles that found in the structural theme of peptide hormone precursors and of the GKR segment for C-terminal amide formation during the processing of peptide hormones. Daintain/AIFIis immunohistochemically localized to microglial cells in the central nervous system, to macrophages, and to tissue-specialized macrophages such as dendritic or Kupffer's cells in the immune system of different tissues. Its weakly insulin-suppressing activity in vitro, dual influence on glucose-stimulated insulin secretion in vivo and relative abundance in macrophages of the pancreatic islets of prediabetic and newly diabetic BB rats raise the possibility that daintain/AIFI has a role in the pathogenesis of insulin dependent diabetes mellitus and other autoimmune diseases.
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- Crenshaw, D. M., et al.
(författare)
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Multiwavelength observations of short-timescale variability in NGC 4151. I. Ultraviolet observations
- 1996
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 322-335335
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Tidskriftsartikel (refereegranskat)abstract
- Presents the results of an intensive ultraviolet monitoring campaign on the Seyfert 1 galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously with the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every ~70 minutes, and during 4 hr periods for 4 days prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 to 2688 Aring went through four significant and well-defined ldquoeventsrdquo of duration 2-3 days during the continuous-monitoring period. The authors find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller timescales (i.e., a few days). The continuum variations in all the UV bands are simultaneous to within an accuracy of ~0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip) and do not correlate well with continuum light curves over the short duration of the campaign, because the timescale for continuum variations is apparently smaller than the response times of the emission lines
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- da Silva, AF, et al.
(författare)
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Impurity resistivity of the double-donor system Si : P,Bi
- 1999
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 60:23, s. 15824-15828
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Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity of the shallow double-donor system Si:P,Bi, prepared by ion implantation, was investigated in the temperature range from 1.7 to 300 K. Good agreement was obtained between the measured resistivities and resistivities calculated by a generalized Drude approach for the same temperatures and dopant concentrations. The critical impurity concentration for the metal-nonmetal transition for the double-doped Si:P,Bi system was found to lie between the critical concentrations of the two single-doped systems, Si:P and Si:Bi. [S0163-1829(99)11747-8].
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- Edelson, R. A., et al.
(författare)
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Multiwavelength observations of short-timescale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability
- 1996
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 364-377377
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Tidskriftsartikel (refereegranskat)abstract
- For pt.III see ibid., vol.470, no.1, p.349-63 (1996). Combines data from the three preceding papers in order to analyze the multi wave-band variability and spectral energy distribution of the Seyfert 1 galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths. The strongest variations were seen in medium-energy (~1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA=6%) variations (uncorrelated with those at lower energies) were seen at soft gamma-ray energies of ~100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 Aring. These data do not probe extreme ultraviolet (1200 Aring to 0.1 keV) or hard X-ray (250 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of lsim0.15 day between 1275 Aring and the other ultraviolet bands, lsim0.3 day between 1275 Aring and 1.5 keV, and lsim1 day between 1275 and 5125 Aring. These tight limits represent more than an order of magnitude improvement over those determined in previous multi-wave-band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (ales-2.5)
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