Visualization of an unstable coiled coil from the scallop myosin rod

Alpha-helical coiled coils in muscle exemplify simplicity and economy of protein design: small variations in sequence lead to remarkable diversity in cellular functions. Myosin II is the key protein in muscle contraction, and the molecule's two-chain alpha-helical coiled-coil rod region--towards the carboxy terminus of the heavy chain--has unusual structural and dynamic features. The amino-terminal subfragment-2 (S2) domains of the rods can swing out from the thick filament backbone at a hinge in the coiled coil, allowing the two myosin 'heads' and their motor domains to interact with actin and generate tension. Most of the S2 rod appears to be a flexible coiled coil, but studies suggest that the structure at the N-terminal region is unstable, and unwinding or bending of the alpha-helices near the head-rod junction seems necessary for many of myosin's functional properties. Here we show the physical basis of a particularly weak coiled-coil segment by determining the 2.5-A-resolution crystal structure of a leucine-zipper-stabilized fragment of the scallop striated-muscle myosin rod adjacent to the head-rod junction. The N-terminal 14 residues are poorly ordered; the rest of the S2 segment forms a flexible coiled coil with poorly packed core residues. The unusual absence of interhelical salt bridges here exposes apolar core atoms to solvent.     

龙海麻鸭自然感染菲莱氏盲肠温扬球虫亚种(Wenyonella philiplevinei caecum)内生殖虫体与组织病变

考察了厦门地区龙海麻鸭盲肠寄生的球虫,经鉴定为菲莱氏盲肠温扬球虫亚种.该球虫寄生于盲肠,卵囊的最早孢子化时间为24 h.组织切片显示内生殖虫体有三型裂殖体,成熟大配子体位于绒毛中部或肠腺上皮细胞核的下方,椭圆形.成熟小配子体位于绒毛中部和基部上皮细胞核的下方,内有50 个以上逗点状小配子.卵囊位于绒毛基部上皮细胞核的下方、绒毛固有层和粘膜肌层.盲肠病理切片显示盲肠绒毛上皮、肠腺上皮细胞遭到破坏,并伴有炎症反应.     

左手卷曲二氧化硅纳米管的制备

依照文献合成一手性两亲小分子化合物.通过溶胶-凝胶复制法,以该手性两亲小分子化合物的自组装体为模板制备了封端的左手卷曲二氧化硅纳米管.对其形成的机理进行了初步的解释.     

螺旋手性SWCNT的尺寸对赖氨酸分子手性转变反应的限域影响

采用量子力学与分子力学组合的ONIOM方法,研究了两种构象的赖氨酸分子限域在螺旋手性单壁碳纳米管内的手性转变机理.结构分析表明:纳米管管径越小,限域在其中的赖氨酸分子骨架形变越明显,手性碳上的氢原子与氨基上氮的氮原子距离越小.势能面计算表明,两种构象的赖氨酸分子限域在SWCNT(6,4)时,旋光异构反应决速步的吉布斯自由能垒分别是194.72和170.08kJ·mol~(-1),分别由质子从手性碳向氨基氮和质子从手性碳向氨基氮与氨基上的质子向羰基氧双质子协同迁移的过渡态产生的.与裸反应的此通道决速步能垒252.6kJ·mol~(-1)相比较有显著降低.两种构象的赖氨酸分子限域在SWCNT(6,4)内旋光异构反应的表观能垒分别是160.00和178.59kJ·mol~(-1).他们限域在SWCNT(7,4)内时,旋光异构反应决速步的能垒分别是238.28和217.18kJ·mol~(-1);限域在SWCNT(8,4)内时,旋光异构反应决速步的能垒分别是253.00和250.11kJ·mol~(-1).结果表明:螺旋手性单壁碳纳米管的孔径越小,对赖氨酸分子手性转变反应的限域催化作用越好;限域在SWCNT(6,4)内的赖氨酸分子构象1更容易旋光异构.     

龙海麻鸭自然感染菲莱氏盲肠温扬球虫亚种(Wenyonella philiplevinei caecum)季节动态及内生殖各期虫体多糖的细胞化学

对厦门地区龙海麻鸭自然感染菲莱氏盲肠温扬球虫亚种的季节动态进行了调查,结果表明一年四季均可感染,其中流行高峰期是３～７月．对盲肠组织进行石蜡切片的细胞化学染色,显明：成熟的裂殖体含有多糖,成熟大配子体、小配子体和卵囊ＰＡＳ反应呈阳性,而滋养体、早期的大小配子体ＰＡＳ反应呈阴性     

Removal of bound calcium from nematocyst contents causes discharge

Nematocysts are the stinging organelles of jellyfish, sea anemones and other cnidarians. Each one consists of a closed capsule filled with fluid. In the resting state, part of the surface of the capsule is inverted, forming a tubular thread, which is everted explosively on excitation. The mechanism of explosion is not yet understood, it may be relevant to exocytosis in general, as the nematocyst is a specialized type of exocytotic secretion originating in the Golgi apparatus. Picken and Skaer observed that the capsular fluid showed a large depression of freezing point, suggesting that the osmotic pressure might be as high as 140 bar. They tentatively ascribed the explosion to a sudden increase in permeability of the capsule wall, allowing a rapid osmotic influx of water. However, there is evidence that the material of the thread itself may be capable of some degree of extension and it has been suggested that osmosis plays no part in discharge. We present here a new theory: that the capsule wall is permeable to water even in the undischarged state; discharge is initiated by an increase in the osmotic pressure of the capsular fluid which is brought about by removal of bound calcium ions.     

螺旋形纳米碳晶须的结构及力学性能

用透射电镜(TEM)观察螺旋形碳晶须的微观形貌,并作选区电子衍射,分析其结构,可知螺旋形碳晶须的结构为六方晶体．由衍射图的圆弧可知,晶体为有结构的石墨多晶．将衍射图与形貌图对应起来,可知C轴与螺旋轴大致平行．将碳晶须放在压片机上加压,碳晶须在30MPa压强下受压15min后,无被损害之现象．     

热轧卷取板的氧化层结构及热力学分析

用电子分析天平测量了热轧卷取板试样表面氧化铁皮的增重,用扫描电子显微镜(SEM)和能谱仪(EDS)观察测量了试样表面氧化皮形貌、氧化层厚度和成分,并用热力学方法进行了分析.结果表明,快速冷却时,试样氧化层形成3层结构,即Fe2O3→Fe2O3、Fe3O4→Fe3O→Fe;延长冷却时间,试样氧化层形成2层结构,即Fe2O3→Fe2O3、Fe3O4→Fe.     

螺旋形碳晶须的CVD法制备及热学性能

用化学气相沉积(CVD)法，以金属粉为催化剂在高温下催化热解乙炔(C2H2)，制备出了螺旋形碳晶须材料．实验结果表明：用化学气相沉积法制备螺旋形碳晶须的最佳温度范围为450-600℃，恒温时间为60～70min，压强为1个大气压．经扫描电镜、X射线衍射仪分析表明，螺旋形碳晶须的直径为130-1000nm．螺距为100—350nm，晶须直径在100nm左右，晶须长度达几百微米．将螺旋形碳晶须放入Ar气中，850℃温度下经历1h，成分结构未变，结晶性更好．     

烟草中亚硝胺含量与烟草溶剂萃取物含量的相关性研究

对不同烟草中的亚硝胺含量和不同极性溶剂萃取物含量进行了测定,并讨论了不同产地、等级的烟草中亚硝胺含量与石油醚、乙醚、二氯甲烷和乙醇萃取物含量之间的关系.发现亚硝胺含量与石油醚萃取物含量呈负对数线性相关,线性相关系数R2=0.837 1,而其余的则无显著相关关系.这些相关性的研究对于指导生产低危害卷烟有着极为重要的作用.     

卧式螺旋管内油—气—水三相流流型的实验研究

在２种不同尺寸的卧式螺旋管上进行了油－气－水三相流流型的实验研究，得到了流型图，对各种流型之间的转变机理进行了讨论和分析，同时给出了各流型之间转变的准则关系式     

螺旋形碳纤维的制备及其储锂性能

用镍片和PCl3分别作为催化剂和助催化剂,通过催化裂解乙炔制备出形貌规整的螺旋形碳纤维。采用扫描电镜(SEM)和X-射线衍射(XRD)对螺旋形碳纤维的组成和结构进行分析。通过恒流充放电、循环伏安(CV)和交流阻抗(EIS)等手段表征螺旋形碳纤维的电化学性能并对其储锂机理进行分析。结果表明,在50mA/g电流密度下,首次放电容量为513mAh/g,充电容量300mAh/g,经30个循环后可逆容量增至314mAh/g。对比分析螺旋形碳纤维与天然石墨的循环伏安曲线和充放电曲线,发现二者的储锂方式明显不同,天然石墨的主要储锂区间在低电位进行,而螺旋形碳纤维的储锂电压区间较宽。这与螺旋形碳纤维中存在着较多微孔和缺陷有关,这种结构有利于锂离子在材料中的快速存储,因此螺旋形碳纤维具有较高的大电流循环性能。     

紫苏营养成分的研究

对紫苏植物的叶、茎、籽中营养成分进行了研究,结果表明:紫苏中含有8种人体必需氨基酸;紫苏叶片中粗蛋白含量较高,为27.8%,β-胡萝卜素含量为56.5 mg/kg;紫苏茎、叶中挥发油含量为0.57%;紫苏油中α-亚麻酸含量为62.73%;研究结果为合理开发利用我国紫苏资源提供了重要依据.     

轴向载荷作用下连续管的抗内压/外挤分析

根据连续管在井下的应力状态,考虑轴向载荷,应用弹性失稳理论和von Mises屈服准则,对理想圆截面管进行抗内压分析,得出连续管的破裂压力.建立椭圆截面管的挤毁压力数学模型;运用有限元软件对连续管的挤毁压力进行计算机模拟分析;并对挤毁压力数学模型和有限元分析结果进行比较,二者吻合.     

Two Jurassic salamanders with stomach contents from Inner Mongolia,China

Conchostracans and corixids are part of the diet of extant salamanders,an ecologically important fact in a lacustrine environment. Here we report their discovery in the guts of the aquatic Jurassic salamanders Jeholotriton paradoxus and Chunerpeton tianyiensis, formerly abundant at Daohugou,Ningcheng County,Inner Mongolia,China.This reveals something of the ecology of this im- portant,ancient,vertebrate and invertebrate assemblage.The new fossil evidence indicates the highly selective feeding of these Jurassic salamanders;Jeholotriton preyed only on juveniles of the conchostracan Euestheria luanpingensis,and Chunerpeton only on the corixid Yanliaocorixa chinensis.We can infer the dietary differences as a consequence of different jaw and hyoid structures; and thus niche partitioning in Jurassic salamanders.