光系统Ⅱ反应中心细胞色素b559结构和功能的研究

植物已经演化出多种保护其免受强光抑制和破坏的机制，从而使植物体在自然界能够应付复杂多变的光照环境。虽然人们早就确定Cyt b-559存在于PSII反应中心内，但目前对其性质与功能的认识还不充分。本工作的目的就是研究Cyt b-559天然分子特性，探讨其生理功能和存在的意义。取得了一些有新意的结果： 1、依据PSII反应中心分离纯化的原理，应用更有效的层析介质DEAE-Sephacel，我们设计了快速高效的从菠菜和水稻中分离纯化Cyt b-559的方法和流程，获得了高纯度的样品。它们在非变性胶电泳中具有相同的泳动性。蛋白组分的HPLC结果证明，纯化的Cyt b-559的确由两个亚基组成，α亚基和β亚基的分子量用我们设计的适合于分析小蛋白的Tricine—SDS—PAGE方法准确测定为9.4kDa和4.5kDa。 2、利用HPLC技术分析了纯化的Cyt b-559样品的色素组成，结果表明Cytb-559中含有Chl α而不含类胡萝卜素分子，这一结果通过吸收光谱和共振拉曼光谱的分析得到进一步地证明。通过等电聚焦方法分析了Cyt b-559的等电点，发现其亚基的等电点相差很大，全蛋白的等电点与...更多D1、D2蛋白的等电点也不相同，推测在体内生理pH条件下它们具有相反带电性而在PSII组装中发挥作用。 3、低温荧光光谱的检测结果表明，Cyt b-559的荧光发射峰位在563nm和666nm;首次证明Cyt b-559可以发出荧光和将电子传递给结合在其上的辅助叶绿素，但传递能力比较低故而导致其荧光特性与PSII反应中心的不相同。Cytb-559的紫外荧光光谱表明Trp残基位于其内部的疏水区域，证明Cyt b-559中的芳香族氨基酸可能在其功能的发挥中起一定作用。 4、通过MCD的分析，发现Cyt b-559中血红素的MCD信号在540—580nm和400—440nm波段，而且光谱形状和强度与PSII反应中心的相一致，说明PSII反应中心该范围内的MCD信号中有Cyt b-559的贡献。FTIR光谱的测定结果证明Cyt b-559血红素的配体是组氨酸，其二级结构中α-螺旋占了一半。此外，还比较了Cyt b-559和PSII反应中心的膜脂成分，发现两者有很大的相似性。不同植物来源的Cyt b-559在许多性质上都表现出高度一致，从一个侧面证明Cyt b-559在进化中的保守性。 5、PSll反应中心发生光破坏时，原初电子供体P680己受到严重破坏。我们发现，在光抑制的最初一段时间内，Cyt b-559吸收峰值发生变化：在受体侧光抑制的条件下，其吸收峰值先略有增加而后才下降，而在供体侧光抑制条件下则相反，说明 Cyt b-559对光抑制的发生非常敏感，可能在光抑制早期保护PSll反应中心。 6、纯化的Cyt b-559的组氨酸含量在照光前后没有显著的变化，说明 PSll反应中心内被破坏的组氨酸不属于Cyt b-559。PSll反应中心所含的组氨酸中有些可被DEPC修饰，但我们的实验结果表明DEPC不能修饰Cyt b-559的组氨酸。这可能有利于Cyt b-559保护功能的发挥。 7、我们观察到，在两种光抑制条件下，LP Cyt b-559光还原和 HP Cyt b-559光氧化具有对pH值的依赖性，说明Cyt b-559在光保护中的作用不仅与其高低电势态有关，而且与其质子化程度有联系。CCCP促进HP Cyt -559释放质子，从而维持循环电子传递。DCBQ和 DCMU在很低浓度时都抑制 Cyt b-559光还原，前者不影响Cyt b-559光氧化而后者在CCCP存在时也会抑制Cyt b-559光氧化。 8、Cyt b-559有定位PSll反应中心其它蛋白的锚蛋白的作用。黄化苗转绿实验证明在 HP Cyt b-559的含量增加超过 45％以后放氧活性开始逐渐增加。Cytb－559从低电势态到高电势态的转变是放氧复合物组装到PSll反应中心的关键步骤之一。在植物正常生长时，Cyt b-559与 P680的其它电于供体发生竟争，起到安全阀门的作用。 9、在逆境条件下，Cyt b-559具有保护PSll反应中心免受强光破坏而起到“分于开关”的作用。我们的实验表明，在室温条件下存在通过Cyt b-559的环式电子流，存在从氧化态LP Cyt b-559到还原态HP Cyt b-559的一个循环，其中的氧化还原变化与质子化／去质子化反应相连。通过与其它血红素蛋白的比较，我们推测 Cyt b-559“分子开关”的关键是：光抑制情况下，铁原子与远端His之间的疏水空穴被氧自由基占据后使得铁进入叶琳中央孔中，迫使近端HIS向叶琳平面位移，从而引起 Cyt b-559构象改变，使电势态发生转变。

EXPERIMENTS ON AQUATIC ECOSYSTEM REGIME SHIFT IN ENCLOSURES NEAR LAKE DIANCHI, CHINA

To discover how a lake converts from a turbid state to clean state, and what drives this process, we constructed controlled enclosure ecosystems and used the ecological remediation method to force ecosystems to convert from the turbid state to the clean state. Our results show that the driving forces include temperature., macrophyte, silver carp and mussel, which form a combined force to drive the controlled ecosystem to switch. There is a threshold existing in treated enclosure ecosystem during the conversion from turbid to clean state. When TP <0.09 mg.L-1, Chl-a <0.036 mg.L-1, transparency >62 cm, TN <2.15 mg.L-1, CODMn <13.7 mg.L-1, tubidity <10, and the number of algal cells <10(6) cells.L-1, the treated ecosystem changes sharply from turbid to clean state. The conversion process can be divided into three phases: turbid state, clean-turbid transitional state as well as clean state, and described with the power function Y = a*X-b (where Y is water parameter, X is time, a and b are constants), which indicates that the shift in the enclosure ecosystem from turbid to clean state is discontinuous.

A C-type lectin associated and translocated with cortical granules during oocyte maturation and egg fertilization in fish

Oocyte maturation and egg fertilization in both vertebrates and invertebrates are marked by orchestrated cytoplasmic translocation of secretory vesicles known as cortical granules. It is thought that such redistribution of cellular content is critical for asymmetrical cell division during early development, but the mechanism and regulation of the process is poorly understood. Here we report the identification, purification and cDNA cloning of a C-type lectin from oocytes of a freshwater fish species gibel carp (Carassius auratus gibelio). The purified protein has been demonstrated to have lectin activity and to be a Ca2+-dependent C-type lectin by hemagglutination activity assay. Immunocytochemistry revealed that the lectin is associated with cortical granules, gradually translocated to the cell surface during oocyte maturation, and discharged to the egg envelope upon fertilization. Interestingly, the lectin becomes phosphorylated on threonine residues upon induction of exocytosis by fertilization and returns to its original state after morula stage of embryonic development, suggesting that this posttranslational modification may represent a critical molecular switch for early embryonic development. (C) 2003 Elsevier Inc. All rights reserved.

Optically controlled quantum dot gated transistors with high on/off ratio

We report the design and fabrication of InAs quantum dot gated transistors, which are normally-on, where the channel current can be switched off by laser illumination. Laser light at 650 nm with a power of 850 pW switches the channel current from 5 mu A to 2 pA, resulting in an on/off ratio of more than 60 dB. The switch-off mechanism and carrier dynamics are analyzed with simulated band structure.

Temperature-dependent transport and spin accumulation in a quantum wire with Rashba spin-orbit interaction

We study the theory of temperature-dependent electron transport, spin polarization, and spin accumulation in a Rashba spin-orbit interaction (RSOI) quantum wire connected nonadiabatically to two normal conductor electrode leads. The influence of both the wire-lead connection and the RSOI on the electron transport is treated analytically by means of a scattering matrix technique and by using an effective free-electron approximation. Through analytical analysis and numerical examples, we demonstrate a simple way to design a sensitive spin-transfer switch that operates without applying any external magnetic fields or attaching ferromagnetic contacts. We also demonstrate that the antisymmetry of the spin accumulation can be destroyed slightly by the coupling between the leads and the wire. Moreover, temperature can weaken the polarization and smear out the oscillations in the spin accumulation.

Electrical control of dynamic spin splitting induced by exchange interaction as revealed by time-resolved Kerr rotation in a degenerate spin-polarized electron gas

Manipulation of the spin degree of freedom has been demonstrated in a spin-polarized electron plasma in a heterostructure by using exchange-interaction-induced dynamic spin splitting rather than the Rashba and Dresselhaus types, as revealed by time-resolved Kerr rotation. The measured spin splitting increases from 0.256 meV to 0.559 meV as the bias varies from -0.3 V to -0.6 V. Both the sign switch of the Kerr signal and the phase reversal of Larmor precessions have been observed with biases, which all fit into the framework of exchange-interaction-induced spin splitting. The electrical control of it may provide a new effective scheme for manipulating spin-selected transport in spin FET-like devices. Copyright (C) EPLA, 2008.

A low-cost CMOS programmable temperature

A novel uncalibrated CMOS programmable temperature switch with high temperature accuracy is presented. Its threshold temperature T-th can be programmed by adjusting the ratios of width and length of the transistors. The operating principles of the temperature switch circuit is theoretically explained. A floating gate neural MOS circuit is designed to compensate automatically the threshold temperature T-th variation that results form the process tolerance. The switch circuit is implemented in a standard 0.35 mu m CMOS process. The temperature switch can be programmed to perform the switch operation at 16 different threshold temperature T(th)s from 45-120 degrees C with a 5 degrees C increment. The measurement shows a good consistency in the threshold temperatures. The chip core area is 0.04 mm(2) and power consumption is 3.1 mu A at 3.3V power supply. The advantages of the temperature switch are low power consumption, the programmable threshold temperature and the controllable hysteresis.

Diode-pumped passively mode-locked YVO4/Nd : YVO4 composite crystal laser with LT-In0.25Ga0.75As saturable absorber

A passively mode-locked all-solid-state YVO4/Nd:YVO4 composite crystal laser was realized with a low temperature (LT) In0.25Ga0.75As semiconductor saturable absorber mirror. The saturable absorber was used as nonlinear absorber and output coupler simultaneously. Both the Q-switch and continous-wave mode locking operation were experimentally realized. At a pump power of 4 W, the Q-switched mode locking changed to continuous wave mode locking. An average output power of 4.1 W with 5 ps pulse width was achieved at the pump power of 12 W, corresponding to an optical-optical conversion efficiency of 34.2%.

Recent progresses of Si-based photonics in chinese main land

Si-based photonic materials and devices, including SiGe/Si quantum structures, SOI and InGaAs bonded on Si, PL of Si nanocrystals, SOI photonic crystal filter, Si based RCE (Resonant Cavity Enhanced) photodiodes, SOI TO (thermai-optical) switch matrix were investigated in Institute of Serniconductors, Chinese Academy of Sciences. The main results in recent years are presented in the paper. The mechanism of PL from Si NCs embedded in SiO2 matrix was studied, a greater contribution of the interface state recombination (PL peak in 850 similar to 900 nm) is associated with larger Si NCs and higher interface state density. Ge dots with density of order of 10(11) cm(-2) were obtained by UHV/CVD growth and 193 nm excimer laser annealing. SOI photonic crystal filter with resonant wavelength of 1598 nm and Q factor of 1140 was designed and made. Si based hybrid InGaAs RCE PD with eta of 34.4% and FWHM of 27 nut were achieved by MOCVD growth and bonding technology between InGaAs epitaxial and Si wafers. A 16x16 SOI optical switch matrix were designed and made. A new current driving circuit was used to improve the response speed of a 4x4 SOI rearrangeable nonblocking TO switch matrix, rising and failing time is 970 and 750 ns, respectively.

High efficiency passively Q-switched mode-locking Nd:GdVO4 laser with LT-In0.25Ga0.75As saturable absorber

The generation of passively Q-switched mode-locking operation with 100% modulation depth has been observed from a diode-pumped Nd GdVO4 laser with a low temperature In0.25Ga0.75As saturable absorber, which was grown by the metal-organic chemical-vapor deposition technique and acted as saturable absorber as well as output coupler. The repetition rate and pulse duration of the mode-locked pulses concentrated in the Q-switch envelop were 455 MHz and 12 ps, respectively. The average output power was 1.8 W and the slope efficiency was 36%. (C) 2009 Elsevier B.V. All rights reserved.

Four-channel reconfigurable optical add-drop multiplexer based on photonic wire waveguide

We designed and fabricated a four-channel reconfigurable optical add-drop multiplexer based on silicon photonic wire waveguide controlled through thermo-optic effect. The effective footprint of the device is about 1000 x 500 mu m(2). The minimum insertion loss is about 10.7 dB and the tuning bandwidth about 17 nm. The average tuning power efficiency is about 6.187 mW/nm and the tuning speed about 24.4 kHz. The thermo-optic polarization-rotation effect is firstly reported in this paper. (C) 2009 Optical Society of America

Electric field driven quantum phase transition between band insulator and topological insulator

We demonstrate theoretically that electric field can drive a quantum phase transition between band insulator to topological insulator in CdTe/HgCdTe/CdTe quantum wells. The numerical results suggest that the electric field could be used as a switch to turn on or off the topological insulator phase, and temperature can affect significantly the phase diagram for different gate voltage and compositions. Our theoretical results provide us an efficient way to manipulate the quantum phase of HgTe quantum wells.

Rearrangeable nonblocking thermo-optic 4 x 4 switching matrix in silicon-on-insulator

A rearrangeable nonblocking thermo-optic 4 x 4 switching matrix is demonstrated. The matrix, which consists of five 2 x 2 multimode interference-based Mach-Zehnder interferometer (MMI-MZI) switch elements, is fabricated in silicon-on-insulator waveguide system. The average excess loss for the optical path experiencing 2 and 3 switch elements is 6.6 and 10.1 dB respectively. The crosstalk in the matrix is measured to be between -12 and -19 dB. The switching time of the device is less than 30 mu s.

Analysis of temperature dependence of silicon-on-insulator thermo-optic attenuator

The temperature dependence of silicon-on-insulator thermo-optic attenuators is analysed, which originates from the temperature dependence of characteristics of multimode interference. The attenuator depth and power consumption are independent of temperature while the insertion loss depends on the temperature heavily. The variation of the insertion loss decreases from 4.3 dB to 1 dB as the temperature increases from 273 K to 343 K.

Electro-optic coefficients of Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice measured by polarization-maintaining fiber-optic Mach-Zehnder interferometer

Ten-period 5.5 nm Si0.75Ge0.25/10.3 nm Si/2.5 nm Si0.5Ge0.5 trilayer asymmetric superlattice was prepared on Si (001) substrate by ultrahigh vacuum chemical vapor deposition at 500 degrees C. The stability of Mach-Zehnder interferometer was improved by utilizing polarization-maintaining fibers. According to the electro-optic responses of the superlattice with the light polarization along [110] and [-110], respectively, both electro-optic coefficients gamma(13) and gamma(63) of such asymmetric superlattice were measured. gamma(13) and gamma(63) are 2.4x10(-11) and 1.3x10(-11) cm/V, respectively, with the incident light wavelength at 1.55 mu m. (c) 2006 American Institute of Physics.