| 1. |
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Michael, Eli, et al.
(författare)
-
Hubble Space Telescope Observations of High-Velocity Lyα and Hα Emission from Supernova Remnant 1987A : The Structure and Development of the Reverse Shock
- 2003
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 593, s. 809-830
-
Tidskriftsartikel (refereegranskat)abstract
- We present two-dimensional line profiles of high-velocity (~+/-12,000 km s-1) Lyα and Hα emission from supernova remnant 1987A obtained with the Space Telescope Imaging Spectrograph between 1997 September and 2001 September (days 3869-5327 after the explosion). This emission comes from hydrogen in the debris that is excited and ionized as it passes through the remnant's reverse shock. We use these profiles to measure the geometry and development of the reverse-shock surface. The observed emission is confined within ~+/-30° about the remnant's equatorial plane. At the equator, the reverse shock has a radius of ~75% of the distance to the equatorial ring. We detect marginal differences (6%+/-3%) between the location of the reverse-shock front in the northeast and southwest parts of the remnant. The radius of the reverse shock surface increases for latitudes above the equator, a geometry consistent with a model in which the supernova debris expands into a bipolar nebula. Assuming that the outer supernova debris has a power-law density distribution, we can infer from the reverse-shock emission light curve an expansion rate (in the northeast part of the remnant) of 3700+/-900kms-1, consistent with the expansion velocities determined from observations in radio (Manchester et al.) and X-ray (Park et al.; Michael et al.) wavelengths. However, our most recent observation (at day 5327) suggests that the rate of increase of mass flux across the northeast sector of the reverse shock has accelerated, perhaps because of deceleration of the reverse shock caused by the arrival of a reflected shock created when the blast wave struck the inner ring. Resonant scattering within the supernova debris causes Lyα photons created at the reverse shock to be directed preferentially outward, resulting in a factor of ~5 difference in the observed brightness of the reverse shock in Lyα between the near and far sides of the remnant. Accounting for this effect, we compare the observed reverse-shock Lyα and Hα fluxes to infer the amount of interstellar extinction by dust as E(B-V)=0.17+/-0.01 mag. We also notice extinction by dust in the equatorial ring with E(B-V)~0.02-0.08 mag, which implies dust-to-gas ratios similar to that of the LMC. Since Hα photons are optically thin to scattering, the observed asymmetry in brightness of Hα from the near and far sides of the remnant represents a real asymmetry in the mass flux through the reverse shock of ~30%. We discuss future observational strategies that will permit us to further investigate the reverse-shock dynamics and resonant scattering of the Lyα line and to constrain better the extinction by dust within and in front of the remnant.
|
|
| 5. |
- Creamer, Lawrence K, et al.
(författare)
-
Heat-Induced Redistribution of Disulfide Bonds in Milk Proteins. 1. Bovine beta-Lactoglobulin
- 2004
-
Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 52:25, s. 7660-7668
-
Tidskriftsartikel (refereegranskat)abstract
- Changes in the structure and chemistry of -lactoglobulin (-LG) play an important role in the processing and functionality of milk products. In model -LG systems, there is evidence that the aggregates of heated -LG are held together by a mixture of intermolecular non-covalent association and heat-induced non-native disulfide bonds. Although a number of non-native disulfide bonds have been identified, little is known about the initial inter- and intramolecular disulfide bond rearrangements that occur as a result of heating. These interchange reactions were explored by examining the products of heat treatment to determine the novel disulfide bonds that form in the heated -LG aggregates. The native protein and heat-induced aggregates were hydrolyzed by trypsin, and the resulting peptides, before and after reduction with dithiothreitol, were separated by high-performance liquid chromatography and their identities confirmed by electrospray ionization mass spectrometry. Comparisons of these peptide patterns showed that some of the Cys160 was in the reduced form in heated -LG aggregates, indicating that the Cys160-Cys66 disulfide bond had been broken during heating. This finding suggests that disulfide bond interchange reactions between -LG non-native monomers, or polymers, and other proteins could occur largely via Cys160.
|
|
| 6. |
|
|
| 7. |
- Jenkins, David J A, et al.
(författare)
-
Effect of wheat bran on glycemic control and risk factors for cardiovascular disease in type 2 diabetes.
- 2002
-
Ingår i: Diabetes care. - 0149-5992. ; 25:9, s. 1522-8
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Cohort studies indicate that cereal fiber reduces the risk of diabetes and coronary heart disease (CHD). Therefore, we assessed the effect of wheat bran on glycemic control and CHD risk factors in type 2 diabetes. RESEARCH DESIGN AND METHODS: A total of 23 subjects with type 2 diabetes (16 men and 7 postmenopausal women) completed two 3-month phases of a randomized crossover study. In the test phase, bread and breakfast cereals were provided as products high in cereal fiber (19 g/day additional cereal fiber). In the control phase, supplements were low in fiber (4 g/day additional cereal fiber). RESULTS: Between the test and control treatments, no differences were seen in body weight, fasting blood glucose, HbA(1c), serum lipids, apolipoproteins, blood pressure, serum uric acid, clotting factors, homocysteine, C-reactive protein, magnesium, calcium, iron, or ferritin. LDL oxidation in the test phase was higher than that seen in the control phase (12.1 +/- 5.4%, P < 0.034). Of the subjects originally recruited, more dropped out of the study for health and food preference reasons from the control phase (16 subjects) than the test phase (11 subjects). CONCLUSIONS: High-fiber cereal foods did not improve conventional markers of glycemic control or risk factors for CHD in type 2 diabetes over 3 months. Possibly longer studies are required to demonstrate the benefits of cereal fiber. Alternatively, cereal fiber in the diet may be a marker for another component of whole grains that imparts health advantages or a healthy lifestyle.
|
|
| 8. |
- Lawrence, A.D., et al.
(författare)
-
Reactions between Ca-based solids and gases representative of those found in a fluidized-bed incinerator
- 2000
-
Ingår i: Chemical Engineering Science. - 0009-2509 .- 1873-4405. ; 55:24, s. 6129-6137
-
Tidskriftsartikel (refereegranskat)abstract
- In the fluidized incineration of municipal solids waste and other fuels containing significant amounts of chlorine, it is possible for limestone, present to capture sulphur, to react with HCl to produce CaCl2. This work considers the fate of CaCl2 as it circulates in a fluidized combustor encountering regions of high O2 and moisture content. Rather than attempting this in a complicated fluidized bed, a thermogravimetric analyzer (TGA) was used: the mass of samples of CaCl2 was measured as a function of time as the solid reacted with various gases. Calcium chloride was reacted with mixtures of gases containing combinations of 0, 3.2 or 11.6 vol% O2, 0, 5, 10 or 20 vol% H2O, 0, 1000 or 2000 vppm SO2 and 0, 1000, 3000 or 5000 vppm HCl. The balance was N2. The temperature range investigated was 680-900 °C. It was found that even in pure N2 there was a slow decrease in the mass of CaCl2, which could be attributed to evaporation. Using 3.2 or 11.6 vol% O2 in N2 resulted in a faster, yet still slow, mass change. In this case, the CaCl2 was being oxidized to CaO. The presence of water greatly increased this reaction such that with 10 vol% water at 900 °C, complete conversion to CaO (releasing HCl) could be achieved. With mixtures of water and HCl, however, the ratio of CaO to CaCl2 in the reacted particle varied with the concentration of water. At moisture levels typically found in combustion products, a fully reacted particle contained about 66 wt% CaO and 34 wt% CaCl2. This degree of conversion, however, took nearly 2 h. In short, limestone is not likely to act as a significant in situ capture method for HCl in a fluidized bed. CaCl2 that is formed will tend to release the HCl as the solid circulates in the fluidized bed.
|
|
| 9. |
- Lee, T W R, et al.
(författare)
-
Precursor of human adenovirus core polypeptide Mu targets the nucleolus and modulates the expression of E2 proteins
- 2004
-
Ingår i: Journal of General Virology. - : Microbiology Society. - 0022-1317 .- 1465-2099. ; 85:Pt 1, s. 185-196
-
Tidskriftsartikel (refereegranskat)abstract
- We have examined the subcellular localization properties of human adenovirus 2 (HAdV-2) preMu and mature Mu (pX) proteins as fusions with enhanced green fluorescence protein (EGFP). We determined that preMu is exclusively a nucleolar protein with a single nucleolar accumulation signal within the Mu sequence. In addition, we noted that both preMu-EGFP and Mu-EGFP are excluded from adenovirus DNA-binding protein (DBP)-rich replication centres in adenovirus-infected cells. Surprisingly, we observed that cells in which preMu-EGFP (but not Mu-EGFP) is transiently expressed prior to or shortly after infection with Ad2 did not express late adenovirus genes. Further investigation suggested this might be due to a failure to express pre-terminal protein (preTP) from the E2 region, despite expression of another E2 protein, DBP. Deletion mutagenesis identified a highly conserved region in the C terminus of preMu responsible for these observations. Thus our data suggest that preMu may play a role in modulating accumulation of proteins from the E2 region.
|
|
| 10. |
- Owenius, Rikard, 1969-
(författare)
-
Studies of Local Interactions between and within Proteins using Site-Directed Labeling Techniques
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Proteins are essential participants in virtually all cellular processes. The key to the understanding of the function of a certain protein is a detailed knowledge about its atomic three-dimensional structure. Presently, there is a huge research effort in the search of increased knowledge about the structure and dynamics of protein complexes, as well as in the pursuit of structural information about conformational changes during protein folding and protein aggregation. The main objective of the work described in this thesis was to acquire new structural and dynamic details of relevant proteins in these categories. The methodology used is based on site-directed labeling, which involves specific attachment of molecular probes that are sensitive to their local environment and therefore can be used as reporters of structure and dynamics in proteins. The applicability of the approach was evaluated with reference to already known structural data.As a model of protein-protein interactions, we have chosen the complex formation between the extracellular part of tissue factor (sTF) and factor VIIa (FVIIa), which is responsible for the initiation of the blood coagulation cascade. Upon association, an extended, multi-domain binding interface is created between the proteins with a very complex binding pattern. Different spectroscopic labels were covalently attached to an engineered cysteine in sTF at positions previously reported as being located in the sTF:FVIIa binding interface. Two spin labels and two fluorescent labels were used, and their response to the changed local environment upon FVIIa binding was monitored by electron paramagnetic resonance (EPR) and fluorescence spectroscopy, respectively. Initially, the properties of the labels and their preferred orientations within the complex were examined with molecular modeling at a specific site, and subsequently this information was used in the interpretation of the spectral data. The conclusion was a tight interaction between sTF and FVIIa in this region of the complex, in fact comparable to that seen in the interior of globular proteins. In an extended study, we found interactions of similar character at multiple sites not only in the interface region between sTF and the first epidermal growth factor-like (EGF1) domain of FVIIa(sTF:EGF1), but also in the region between sTF and the γ-carboxyglutamic acid (Gla) domainof FVIIa (sTF:Gla). In addition, signs of a tight interaction were found in tlte interface region between sTF and the protease domain (PD) in FVIIa (sTF:PD) in spite of the structural perturbation caused by the attached label. By the same approach we suggest that the EGF1 domain of FVIIa does not require assistance from the neighboring Gla domain to establish a rigid native binding to sTF. Furthermore, the interaction between sTF and EGF1 is largely dictated by Ca2+ binding to the site in EGF1. Finally, we monitored conformational changes along the sTF:FVIIa binding interface induced by the incorporation of an inhibitor into the active site of the protease domain of FVIIa. A tighter binding between sTF and FVIIa was detected only in the sTF:PD region, whereas the sTF:EGF1 and sTF:Gla regions were unaffected. The combined use of different spectroscopic techniques and labels (multi-probing) provides valuable complementary information, enabling the comparison of interaction tightness and interaction characteristics, respectively, along the binding interface of a protein complex. The approach also reduces the risk of misinterpretation of data.The enzyme human carbonic anhydrase II (HCAII) was chosen as a model protein for studies of protein folding and aggregation. HCAII unfolds in a multi-step manner with a molten-globule intermediate state populated between the native and unfolded states. Position 79 in the periphery of the central hydrophobic core of HCAII, was labeled with the same four spectroscopic labels as above. A persistent local cluster associated to the central core was observed in the unfolded state, suggesting an extended residual structure. HCAII is known to form aggregates in its partially unfolded molten-globule intermediate state. We found that the formed aggregates at the site of the labels represent an ensemble of different structures with apolar, compact as well as polar, dynamic regions.Finally, spin labels can be applied to proteins not only as probes of local structure but also as probes of local polarity. Therefore, a combined theoretical and experimental work was initiated to assess the sensitivity of spin labels such as MTSSL to various solvents and clarify the influence of solvent polarity (dielectric constant, ε) and proticity. We believe that such information can be useful in the interpretation of rigid-limit data from spin-labeled proteins. The g-values giso and gxx as well as the hyperfine coupling constants Aiso and Azz of the spinlabel were dependent on the solvent properties. At lower polarity (ε<25), the sensitivity of Aiso and Azz to ε is large, whereas at higher polarity (ε>25), the sensitivity to ε is small, so Aiso and Azz are instead determined by the proticity of the solvent. From the comparison of experimental and calculated data the propensity of hydrogen bonding of the solvents was estimated. The density functional theory (DFT) method determines the shifts in giso and gxx due to hydrogen bonding more accurately compared to the restricted open-shell Hartree-Fock method.
|
|
