Effects of ATP and vanadate on calcium efflux from barnacle muscle fibres

Calcium ions carry the inward current during depolarization of barnacle muscle fibres and are involved in the contraction process. Intracellular ionized calcium ([Ca2+]i) in barnacle muscle, as in other cells, is kept at a very low concentration, against a large electrochemical gradient. This large gradient is maintained by Ca2+ extrusion mechanisms. When [Ca2+]i is below the contraction threshold, Ca2+ efflux from giant barnacle muscle fibres is, largely, both ATP dependent and external Na+ (Na+0) dependent (see also refs 5,6). When [Ca2+]i is raised to the level expected during muscle contraction (2-5 muM), most of the Ca2+ efflux from perfused fibres is Na0 dependent; as in squid axons, this Na+0-dependent Ca2+ efflux is ATP independent. Orthovanadate is an inhibitor of (Na+ + K+) ATPase and the red cell Ca2+-ATpase. We report here that vanadate inhibits ATP-promoted, Na+0-dependent Ca2+ efflux from barnacle muscle fibres perfused with low [Ca2+]i (0.2-0.5 microM), but has little effect on the Na+0-dependent, ATP-independent Ca2+ efflux from fibres with a high [Ca]i (2-5 microM). Nevertheless, ATP depletion or vanadate treatment of high [Ca2+]i fibres causes an approximately 50-fold increase of Ca2+ efflux into Ca2+-containing lithium seawater. These results demonstrate that both vanadate and ATP affect Ca2+ extrusion, including the Na+0-dependent Ca2+ efflux (Na-Ca exchange), in barnacle muscle.     

Protein folding in mitochondria requires complex formation with hsp60 and ATP hydrolysis

Mitochondrial heat-shock protein hsp60 functions in the folding of proteins imported into mitochondria. Folding occurs at the surface of hsp60 in an ATP-mediated reaction, followed by release of the bound polypeptides. We propose that hsp60 catalyses protein folding.     

Sliding distance between actin and myosin filaments per ATP molecule hydrolysed in skinned muscle fibres

Muscle contraction is generally thought to be driven by tilting of the 19-nm-long myosin head, part of the thick filament, while attached to actin, part of the thin filament. This motion would produce about 12 nm of filament sliding. Recent estimates of the sliding distance per ATP molecule hydrolysed by actomyosin in vitro vary widely from 8 nm to greater than or equal to 200 nm. The latter value is incompatible with a power stroke incorporating a single tilting motion of the head. We have measured the isotonic sliding distance per ATP molecule hydrolysed during the interaction between myosin and actin in skinned muscle fibres. We directly estimated the proportion of simultaneously attached actomyosin complexes and their ATP use. We report here that at low loads the interaction distance is at least 40 nm. This distance corresponds to the length of the power stroke plus the filament sliding while actomyosin crossbridges bear negative drag forces. If the power stroke is 12 nm, then our results indicate the drag distance to be at least 28 nm. Our results could also be explained by multiple power strokes per ATP molecule hydrolysed.     

净化槽水质改善与植物生理日变化关系的研究

试验设定曝气和非曝气的两组工况植物净化槽,在一天中不同时间点测定净化槽的出水水质及植物根组织过氧化物酶(POD)、过氧化氢酶(CAT)活性与叶片可溶性蛋白(SP)、叶绿素(Chla)含量.分析了污染物去除与植物(睡莲)生理特性日变化的相关性及曝气对水质净化及植物生理的影响机制.结果表明:两组工况净化槽内植物生理特性与水质理化指标均在一定程度上受到光强变化的影响,植物根组织POD,CAT活性及叶片Chla,SP含量与净化槽DO浓度,CODCr,NH4+-N和TP去除率间呈正相关;曝气对植物根组织POD,CAT活性及叶片SP,Chla含量影响显著;曝气净化槽的出水DO浓度,CODCr,NH4+-N和TP去除率分别高出非曝气净化槽2.54mg/L,21.0%,16.6%和14.1%.     

油/水两相水解精制六氯环三磷腈的研究

提出了油/水两相水解法精制六氯环三磷腈工艺。将4 g粗六氯环三磷腈溶于30 mL石油醚(90~120℃)中,按1∶2(mL/mL)的油水比加入蒸馏水,温度60℃下剧烈搅拌8 h,5℃水中结晶,精制六氯环三磷腈纯度达98.3%,收率76.1%。     

科技智库研究方法:进展与趋势

 对全球科技智库的学科领域、理论体系、具体方法以及实践成果进行了调研与分析。调研结果显示,经济管理、政治法律、安全社会、能源环境等学科领域是科技智库研究方法关系网的核心,交通建筑、天文地学、生物医药、材料化学、数学物理、信息通信等学科领域处于辅助地位。科技智库的研究理论经由科技规划、科技评估、科技路线图的实践,逐渐向DⅡS研究体系发展。科技智库研究的具体方法可分为数据收集方法、信息整合方法、综合研判方法、方案构建方法4类,具有多主体、多对象、多介质、多因子、多组合、多渠道、多层次、多维度、多阶段、多角色等特征。随着科学技术在公共服务和决策咨询中的应用,科技智库的研究方法以可视化平台、跟踪调查平台、综合检索平台为依托,将进一步深化、拓展、完善。     

Sliding distance of actin filament induced by a myosin crossbridge during one ATP hydrolysis cycle

Muscle contraction results from a sliding movement of actin filaments induced by myosin crossbridges on hydrolysis of ATP, and many non-muscle cells are thought to move using a similar mechanism. The molecular mechanism of muscle contraction, however, is not completely understood. One of the major problems is the mechanochemical coupling at high velocity under near-zero load. Here, we report measurements of the sliding distance of an actin filament induced by a myosin crossbridge during one ATP hydrolysis cycle in an unloaded condition. We used single sarcomeres from which the Z-lines, structures which anchor the thin filaments in the sarcomere, had been completely removed by calcium-activated neutral protease (CANP) and trypsin, and measured both the sliding velocity of single actin filaments along myosin filaments and the ATPase activity during sliding. Our results show that the average sliding distance of the actin filament is less than or equal to 600 A during one ATP cycle, much longer than the length of power stroke of myosin crossbridges deduced from mechanical studies of muscle, which is of the order of 80 A (for example, ref. 15).     

水环境中农药的水解研究分析

残留在水环境中的农药受到各种生物和非生物因素的影响,会发生复杂的蓄积和降解行为。通过对国内外关于水环境中农药的水解的影响因素和降解机理研究进行总结和归纳,综述了农药的水解动力学规律及水解机理,给出了综合性结论,即农药的水解机理主要是亲核取代反应历程。在一定的温度和pH值条件下,农药的水解遵从一级反应动力学规律,水环境的pH值决定了农药水解的反应速率。     

水解酸化工艺改善油田采出水生物降解性能

研究了水解酸化工艺改善难生物降解油田采出水的生物降解性能及其有机物去除效果．结果表明,在污泥量为25000 mg/L,HRT为8h条件下,采出水中石油类物质降低到了10 mg/L以下,挥发酚类物质降低到了未检出水平,生物降解性能得到了较大改善,其BOD_5/COD提高了17%,为后续好氧生物处理提供了良好的基质准备．工艺抗毒性和冲击负荷能力较强,出水稳定．     

依托解吸-深度水解装置实现尿素废水零排放

采用解吸-深度水解技术,处理尿素工艺冷凝液、一甲泵密封水及合成塔和一甲泵冲洗水,回收废水中的氨和尿素,同时将冷凝液进行回收用作脱盐水的补充水,实现尿素废水零排放,具有较好的环境效益和经济效益和社会效益。     

用于光测电压的晶体的选择及光轴选定

介绍了用于光测电压的晶体的选择与晶体加工设计中的光轴选定原则。以ＬＮ晶体为例介绍了晶体元件设计过程中的参数计算方法     

Kinetics of non-catalyzed hydrolysis of tannin in high temperature liquid water

High temperature liquid water （HTLW） has drawn increasing attention as an environmentally benign medium for organic chemical reactions, especially acid-/base-catalyzed reactions. Non-catalyzed hydrolyses of gallotannin and tara tannin in HTLW for the simultaneous preparation of gallic acid （GA） and pyrogallol （PY） are under investigation in our laboratory. In this study, the hydrolysis kinetics of gallotannin and tara tannin were determined. The reaction is indicated to be a typical consecutive first-order one in which GA has formed as a main intermediate and PY as the final product. Selective decomposition of tannin in HTLW was proved to be possible by adjusting reaction temperature and time. The present results provide an important basic data and reference for the green preparation of GA and PY.     

厌氧水解滤池污水处理过程中水质的变化

污水经厌氧水解滤池处理后,污染物的浓度和性质发生了变化,BOD5/COD增加,溶解性COD比例增加,可生化性和碱度都得到提高,COD和SS去除率高,反应器中污泥得到充分处理,出水中脂肪酸含量增加,氧化还原电位在好氧滤池和厌氧消化池之间。水解滤池中有机物的降解经历了快速吸附和截留过程及慢慢分解过程。     

超微粉碎辅助提取玉米皮水溶性膳食纤维的研究

以玉米皮为原料,利用超微粉碎与酶解技术提取玉米皮水溶性膳食纤维,并通过单因素实验和正交试验确最佳制备工艺条件。结果表明,玉米皮超微粉粒径为38～45μm,酶解温度55℃,酶解时间为2.5 h,酶添加量为0.8%,料液比为1∶23(g/mL)时,玉米皮水溶性膳食纤维得率最高,为13.69%。