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排序方式: 共有764条查询结果,搜索用时 15 毫秒
761.
Brinkmalm G Portelius E Öhrfelt A Mattsson N Persson R Gustavsson MK Vite CH Gobom J Månsson JE Nilsson J Halim A Larson G Rüetschi U Zetterberg H Blennow K Brinkmalm A 《Journal of mass spectrometry : JMS》2012,47(5):591-603
Amyloid precursor protein (APP) is the precursor protein to amyloid β (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD). Endogenous Aβ peptides reflect the APP processing, and greater knowledge of different APP degradation pathways is important to understand the mechanism underlying AD pathology. When one analyzes longer Aβ peptides by low-energy collision-induced dissociation tandem mass spectrometry (MS/MS), mainly long b-fragments are observed, limiting the possibility to determine variations such as amino acid variants or post-translational modifications (PTMs) within the N-terminal half of the peptide. However, by using electron capture dissociation (ECD), we obtained a more comprehensive sequence coverage for several APP/Aβ peptide species, thus enabling a deeper characterization of possible variants and PTMs. Abnormal APP/Aβ processing has also been described in the lysosomal storage disease Niemann-Pick type C and the major large animal used for studying this disease is cat. By ECD MS/MS, a substitution of Asp7 → Glu in cat Aβ was identified. Further, sialylated core 1 like O-glycans at Tyr10, recently discovered in human Aβ (a previously unknown glycosylation type), were identified also in cat cerebrospinal fluid (CSF). It is therefore likely that this unusual type of glycosylation is common for (at least) species belonging to the magnorder Boreoeutheria. We here describe a detailed characterization of endogenous APP/Aβ peptide species in CSF by using an online top-down MS-based method. 相似文献
762.
763.
The force dependence of the ball indentation hardness can be described in many cases by MEYER's hardness law. The characteristic material parameters are the MEYER constant K and the MEYER exponent n. But often other simple measures of hardness are used for technical applications. Examples are the difference of hardness for two different loads, which gives a good view of the hardening capability of the material, and the BRINELL hardness. It is shown that empirical found relations between the mentioned measures of hardness and the MEYER parameters are strong consequences of the validity of MEYER'S law. In special ranges of the values of the material parameters these empirical relations are linear ones. As a result of the theoretical considerations one must recommend to use the theoretical relations to fit the experimental values, because only in this case all physical conditions are fulfiled automatically. 相似文献
764.
Gerald Gerlach Margarita Guenther Gunnar Suchaneck Joerg Sorber Karl-Friedrich Arndt Andreas Richter 《Macromolecular Symposia》2004,210(1):403-410
In the present work, pH-sensitive poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) blends as well as hydrogels based on poly(N-isopropylacrylamide) (PNIPAAm), which are sensitive to organic solvent concentration in aqueous solutions, were used in silicon micromachined sensors. A sensitivity of approximately 15 mV/pH was obtained for a pH sensor with a 50 μm thick PVA/PAA hydrogel layer in a pH range above the acid exponent of acrylic acid (pKa=4.7). The output voltage versus pH-value characteristics and the long-term signal stability of hydrogel-based sensors were investigated and the measurement conditions necessary for high signal reproducibility were determined. The influence of the preparation conditions of the hydrogel films on the sensitivity and response time of the chemical and pH sensors is discussed. 相似文献