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81.
82.
    
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   
83.
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   
84.
Enzyme activity, protein contents, and mRNA contents of group II phospholipase A2 (PLA2) in hepatocellular carcinoma (HCC) surgically obtained from 8 patients were compared with those in either its neighboring liver tissues or control liver tissues. The PLA2 specific activity towards the mixed micelles of 1-palmitoyl-2-oleoyl-phosphatidylglycerol and cholate was significantly greater in the tumor tissues (6.62 ± 1.46 nmol/min/mg) than those in the surrounding liver tissues (1.33 ± 0.22 nmol/min/mg) and controls (0.43 ± 0.04 nmol/min/mg). The results of immunoblot analysis using a specific anti-human group II PLA2 antibody and of Northern blot analysis using a human group II PLA2 cDNA as a probe demonstrated that group II PLA2 was responsible for the increased enzyme activity. The contents of immunoreactive group II PLA2 in the tumor tissues (8.81 ± 1.24 ng/mg) were significantly higher than those in the surrounding liver tissues (1.77 ± 0.27 ng/mg); those in the control tissues were below the analytical range of the method used. The group II PLA2 mRNA was also significantly increased in the tumor tissues, compared with that in the surrounding liver tissues, whereas it was not detectable in th controls. This indicates that group II PLA2 in HCC is induced at the pretranslational level.  相似文献   
85.
86.
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   
87.
零下低温对杂交杨树皮层膜脂组成的影响   总被引:3,自引:0,他引:3  
以不耐寒的美洲黑杨(Populusdeltoidescv.“Lux”I-69/55,父本)和耐寒性较强的欧美杨(P.euramericanaclcv.I-45/51,母本)的4个杂交F_1代无性系(95杨、559杨、600杨和1381杨)为材料,分析了零下低温寒潮前后枝条皮层的脂质组成。结果表明,寒潮影响下,皮层中磷脂含量增加而组成基本不变,膜脂脂肪酸组成的变化规律是:寒潮前脂肪酸不饱和指数(IUFA)值大的无性系,寒潮前后的IUFA值变化量小;寒潮前IUFA值较小的无性系,寒潮前后IUFA值变化量较大。本文借用力学概念,提出相对抗性概念,给出杨树无性系的相对抗性序列。序列表明F_1代无性系的耐寒性已较不耐寒的父本提高,这与田间观察基本一致。  相似文献   
88.
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   
89.
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  
王明倩 《古生物学报》1993,32(4):458-476
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   
90.
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   
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