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71.
Uri S. Ladror Gary T. Wang William L. Klein Thomas F. Holzman Grant A. Krafft 《Journal of Protein Chemistry》1994,13(4):357-366
Fluorogenic peptide substrates designed to encompass the reported-secretory and amyloidogenic cleavage sites of the amyloid- precursor protein (PP) were used to analyze proteinase activities in brain extracts from control patients and those with Alzheimer's disease (AD). Activity against the secretory substrate atpH 7.5 in control and AD brains produced a major endopeptidase cleavage at the Lys687-Leu688 bond (PP770 numbering), consistent with thePP secretase cleavage. Activity in control brains against the amyloidogenic substrate atpH 7.5 produced one cleavage at the Ala673-Glu674 bond, two residues C-terminal to the amyloidogenic Met-Asp site. However, in three of four AD brains, the major cleavage was at the Asp-Ala bond, one residue from the amyloidogenic site. Both endopeptidase and carboxypeptidase activities in AD brains were lower than in control brains. Proteinase activities against the secretory substrate had a major optimum atpH 3.0–4.0 and another atpH 6.0–7.5. Proteinase activities against the amyloidogenic substrate had a major optimum at or belowpH 3.0 and another atpH 6.0. Using both substrates, activities at lowpH were higher in AD brains than in controls, while atpH above 6.5, activities in control brains were higher than in AD. These results indicate that the levels of proteolytic enzymes in AD brains are altered relative to controls.Abbreviations A
Amyloid-
- ACN
acetonitrile
- AD
Alzheimer's disease
- PP
amyloid- precursor protein
- DABCYL
4-(4-dimethylaminophenylazo)-benzoic acid
- EDANS
5-{(2-aminoethyl)amino}napthalene-1-sulfonic acid
- MES
morpholinoethane sulfonic acid
- MOPS
morpholino-propane sulfonic acid
- RP-HPLC
reverse-phase high-performance liquid chromatography
- SDS-PAGE
sodium do-decyl sulfate-polyacrylamide gel electrophoresis
- TFA
tri-fluoroacetic acid
- Tris
tris(hydroxyethyl)aminomethane 相似文献
72.
Absence of effects of low-frequency, low-amplitude magnetic fields on the properties of gramicidin A channels. 下载免费PDF全文
The effects of static and low-frequency magnetic fields on gramicidin A channels have been investigated using bilayer patch clamp recording and a bridge technique capable of detecting 0.3% changes in the conductance of glyceryl monooleate membranes containing many channels. In the bridge technique the conductance was assessed using 10-ms voltage pulses applied at 10 Hz. Measurements were made for LiCl, KCl, and CsCl using magnetic fields of 50, 100, 500, and 5000 microT with the frequency scanned from 10-200 Hz. The combinations of static and low-frequency fields employed include the "cyclotron resonance" conditions at which effects had been predicted to occur. In no case was there any detectable change in conductance when the magnetic fields were applied or changed. Potassium currents through single gramicidin channels have been recorded for patches in which several channels may be open at once. Fields were applied for 2 min periods interleaved with 2 min controls. Methods have been developed to analyze the multichannel records to reveal the amplitude and duration of the channels together with the frequency, depth, and apparent period of flickers. No significant differences were observed between the control and field-exposed recording periods. The peak of the distribution of opening and closing transitions always coincided for fields on and off within the resolution, 0.4%, of the recordings. There are at least two types of flicker, one with typical period less than 0.1 ms, the other with typical period from 0.3-0.8 ms. Most of the latter were not complete closures with the conductance during a flicker 15-20% above the level for a full closure. 相似文献
73.
74.
本文用细胞免疫化学方法,在冰冻切片上,检测了胎儿不同组织和器官内带γδ和αβ受体的T细胞(TCR)的分布,结果发现TCR细胞的分布与,般T细胞不同,有相对固定的分布区,如胸腺内TCR细胞主要分布在皮筋质交界处和髓质部;脾脏内的γδT主要位于边缘区,而αβT主要位于动脉周围淋巴鞘,在红髓和血窦两种细胞共存;淋巴结内只有少数TCR细胞位于滤泡间或副皮质,滤泡内则未见。消化管内的TCR细胞主要分布在小肠的固有膜,而胃、大肠和阑尾的固有膜内很少见;肝内TCR细胞主要集中在血管和血窦周围;皮肤切片内的少数TCR细胞见于真皮内,表皮基底层细胞内未见。这些细胞在胎儿期的免疫皮应及其生理功能还不清楚。 相似文献
75.
本文报导了胰腺提取物中两种可被钙/钙调素依赖性蛋白激酶磷酸化的热稳定蛋白。SDS-PAGE测定其表观分子量分别为17.7kD和6kD。经钙/钙调素依赖性蛋白激酶磷酸化后,其最大磷酸参入量为8.8μmol/g蛋白。同时磷酸化作用导致17.7kD蛋白在SDS-PAGE中迁移率发生变化。本文还进一步分析了各种阳离子对磷酸化的影响,并对此两种蛋白可能具有的生理功能进行了初步探讨。 相似文献
76.
福建永安丰海二叠系上部及三叠系底部的双壳类动物群* 总被引:2,自引:0,他引:2
系统研究了闽西永安丰海地区二叠系上部及三叠系下部的双壳类动物群面貌、层位及组合,并与国内外相当的地层进行了对比,阐明了该双壳动物群在二叠-三叠系界线划分中的地层意义.描述了15属24种(其中5新种)、5未定种. 相似文献
77.
A novel method is described for the on-line determination of viable cell number. It has been tested in fermentations of Escherichia coli. The cells are transfected with the gene for firefly luciferase and fed low levels of luciferin in the medium. The reaction requires ATP, so the nonviable cells cannot produce light. Thus, light production is linear with viable cell density from innoculation through most of exponential growth. The light emitted by these cells is then conducted from the reaction vessel to the light detection equipment by an optical fiber. With the equipment described below, as few as a 10(6) cells/mL, or an OD(600) of 0.004, are easily detectable and concentrations greater than 10(10) cells/mL are well within range. The data are collected by a computer, so adaptation to on-line control applications is straightforward. During lag phase, this method is much more accurate then optical density measurements. At the end of exponential growth, rapid changes in light production mark carbon source depletion and the onset of cell lysis. A simple model accounts for the luciferin used during the fermentation and corrects the light detected to the proper cell density. (c) 1993 John Wiley & Sons, Inc. 相似文献
78.
用Northern blot方法对二乙基亚硝胺所诱发的大鼠肝癌中内源性蛋白酶抑制因子α_2-巨球蛋白(α_2-M)、非特异性免疫抑制剂α_1-酸性糖蛋白(α_1-AGP)及雄性激素正调控的α-2u球蛋白(α-2u)三种分泌性蛋白基因表达情况进行了分析。结果表明在大部分(14/16)肝癌样品中α_2-M RNA水平显著降低;而α_1-AGP RNA水平显著高于正常对照水平;α-2u RNA水平明显下降,但在某些雄性大鼠肝癌样品中该基因却有一定程度的表达。这些结果说明,一些肿瘤宿主血浆中α_2-M水平的显著下降及α_1-AGP水平的明显升高分别是由于基因表达活性的下降及升高所致。α-2u基因表达的异常提示,在癌变过程中机体的内分泌功能发生了某些变化。 相似文献
79.
利用蛋白质内源荧光和酶活性两种信号以及荧光偏振,HPLC和停流等方法研究了盐酸胍诱导的α淀粉酶去折叠与重折叠的平衡转变和动力学。实验结果表明α淀粉酶去折叠与重折叠是两个不同的过程;变性与复性过程中可能伴有聚集体生成;去折叠与重折叠均为双相过程,重折叠大约始于2秒之后。 相似文献
80.
Wang Zheng-yi 《Biotechnic & histochemistry》1993,68(1):38-41
A new antiroll device has been developed to replace the antiroll guide plate for cryostat wax sectioning. With this device, a continuous ribbon of 3-4 μm sections can be obtained. The sections are flat, uncreased. and compression is reduced to a minimum. 相似文献