Circularly polarized chlorophyll luminescence reflects the macro-organization of grana in pea chloroplasts

Circular polarization of luminescence (CPL; Steinberg IZ (1978) Annu Rev Biophys Bioeng 7: 113–137) was applied to study pea chloroplasts in different structural states. The structural changes of chloroplasts were induced by variation of osmotic pressure, concentration of magnesium-ions or photoinhibition. Both large CPL and psi-type circular dichroism (psi, polymerization and salt induced) signals appeared in the presence of granal macrostructure and were sensitive to structural changes of the grana. The relation was studied between the amount of CPL expressed as an emission anisotropy factor g _em and amplitudes of the red psi-type CD bands. The positive psi-type CD band was not directly correlated with g _em possibly due to a large contribution of circular intensity differential scattering to the measured CD spectra. However, a linear correlation between the amplitude of the negative psi-type CD band and g _em was found. The CPL signal of pea chloroplasts was attributed to a psi-type origin, which is observed in macroaggregates with densely packed chromophores with a long-range chiral order, and directly depends on the level of macroorganization. With the use of CPL-based microscopy, the long-range packing of LHC II particles can be studied in individual chloroplasts in future. In addition, the CPL method in general allows the study of the macro-organization of grana in green leaves, where conventional light-transmission methods fail. This revised version was published online in June 2006 with corrections to the Cover Date.     

Alpha-chymotrypsin catalysis in imidazolium-based ionic liquids

The transesterification reaction of N-acetyl-L-phenylalanine ethyl ester with 1-propanol catalyzed by alpha-chymotrypsin was examined in the ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF(6)]), and in combination with supercritical carbon dioxide (SC-CO(2)). The activity of alpha-chymotrypsin was studied to determine whether trends in solvent polarity, water activity, and enzyme support properties, observed with this enzyme in conventional organic solvents, hold for the novel environment provided by ionic liquids. alpha-Chymotrypsin freeze-dried with K(2)HPO(4), KCl, or poly(ethylene glycol) demonstrated no activity in [bmim][PF(6)] or [omim][PF(6)] at very low water concentrations, but moderate transesterification rates were observed with the ionic liquids containing 0.25% water (v/v) and higher. However, the physical complexation of the enzyme with poly(ethylene glycol) or KCl did not substantially stimulate activity in the ionic liquids, unlike that observed in hexane or isooctane. Activities were considerably higher in [omim][PF(6)] than [bmim][PF(6)]. Added water was not necessary for enzyme activity when ionic liquids were combined with SC-CO(2). These results indicate that [bmim][PF(6)] and [omim][PF(6)] provide a relatively polar environment, which can be modified with nonpolar SC-CO(2) to optimize enzyme activity.     

Conformational behavior of ionic self-complementary peptides

Several de novo designed ionic peptides that are able to undergo conformational change under the influence of temperature and pH were studied. These peptides have two distinct surfaces with regular repeats of alternating hydrophilic and hydrophobic side chains. This permits extensive ionic and hydrophobic interactions resulting in the formation of stable beta-sheet assemblies. The other defining characteristic of this type of peptide is a cluster of negatively charged aspartic or glutamic acid residues located toward the N-terminus and positively charged arginine or lysine residues located toward the C-terminus. This arrangement of charge balances the alpha-helical dipole moment (C --> N), resulting in a strong tendency to form stable alpha-helices as well. Therefore, these peptides can form both stable alpha-helices and beta-sheets. They are also able to undergo abrupt structural transformations between these structures induced by temperature and pH changes. The amino acid sequence of these peptides permits both stable beta-sheet and alpha-helix formation, resulting in a balance between these two forms as governed by the environment. Some segments in proteins may also undergo conformational changes in response to environmental changes. Analyzing the plasticity and dynamics of this type of peptide may provide insight into amyloid formation. Since these peptides have dynamic secondary structure, they will serve to refine our general understanding of protein structure.     

Influence of Short-Chain Aliphatic Acids on the Phenanthrene Desorption and Mobilization from Contaminated Soil

This study was performed to investigate the influence of short-chain aliphatic acids (SCAAs) on the desorption of phenanthrene from artificially contaminated soils with this polycyclic aromatic hydrocarbon. Five SCAAs examined, including acetic acid, oxalic acid, malic acid, tartaric acid and citric acid, were related to the increase of phenanthrene desorption from two kinds of soil. Citric acid and oxalic acid enhanced phenanthrene desorption to a more significant extent than other organic acids. The effects of pH, SCAA concentration, and ionic strength were further evaluated. The phenanthrene desorption was enhanced as the pH increased. An increase in desorbed phenanthrene from pH 3 to pH 8 was observed, but that was followed by a slight decrease above pH 8 for most SCAAs. The phenanthrene desorption performance showed increments with increasing organic acid concentrations. However, the increase of phenanthrene desorption became less remarkable when SCAA concentrations were above 100 mmol/L. Moreover the results suggested that high ionic strength hindered the desorption of phenanthrene in the presence of SCAAs.     

奥卡西平对偏头痛大鼠三叉神经节神经元钙电流的影响*

目的:研究奥卡西平(Oxcarbazepine,OXC)对大鼠三叉神经节神经元钙电流的调控作用。方法:SD大鼠随机分为3组(n=8):生理盐水组(NS组),致炎剂组(IS组),OXC预防组。应用膜片钳技术,采用全细胞记录方式,观察OXC对偏头痛大鼠急性分离的三叉神经节的高电压激活钙电流(HVA-ICa)的调控作用。结果:OXC能够抑制钙电流,使钙电流的激活曲线向去极化方向移动,使钙电流的失活曲线向超级化方向移动。结论:OXC可能通过抑制钙离子进入细胞膜,来预防偏头痛的发作。同时OXC可能对外周神经系统及伤害感受的传入的兴奋性起到调控作用。     

Calcium and salinity as selective factors in plate morph evolution of the three-spined stickleback (Gasterosteus aculeatus)

Identifying the causal factors underlying natural selection remains a key challenge in evolutionary biology. Although the genetic basis for the plate morph evolution of three-spined stickleback (Gasterosteus aculeatus) is well described, the environmental variables that form the basis for different morphs are not understood. We measured the effects of dissolved calcium and salinity on the growth of sticklebacks with different plate morphs from Scotland and Poland. There was a significant interaction of calcium with plate morph for fish from both regions, with complete morph sticklebacks growing more slowly at low calcium concentrations and low morph sticklebacks showing divergent responses to calcium concentration. A Scottish anadromous population showed evidence of local adaptation to high salinity, which was independent of plate morph. Polish and Scottish populations diverged in their response to salinity, suggesting a difference in osmotic regulation. The results implicate a role for calcium in selecting for plate morph evolution in sticklebacks, possibly as a limiting element in skeletal growth.     

Reduced brain levels of DHEAS in hepatic coma patients: significance for increased GABAergic tone in hepatic encephalopathy

Increased neurosteroids with allosteric modulatory activity on GABA(A) receptors such as 3α-5α tertrahydroprogesterone; allopregnanolone (ALLO), are candidates to explain the phenomenon of "increased GABAergic tone" in hepatic encephalopathy (HE). However, it is not known how changes of other GABA(A) receptor modulators such as dehydroepiandrosterone sulfate (DHEAS) contribute to altered GABAergic tone in HE. Concentrations of DHEAS were measured by radioimmunoassay in frontal cortex samples obtained at autopsy from 11 cirrhotic patients who died in hepatic coma and from an equal number of controls matched for age, gender, and autopsy delay intervals free from hepatic or neurological diseases. To assess whether reduced brain DHEAS contributes to increased GABAergic tone, in vitro patch clamp recordings in rat prefrontal cortex neurons were performed. A significant reduction of DHEAS (5.81±0.88 ng/g tissue) compared to control values (9.70±0.79 ng/g, p<0.01) was found. Brain levels of DHEAS in patients with liver disease who died without HE (11.43±1.74 ng/g tissue), and in a patient who died in uremic coma (12.56 ng/g tissue) were within the control range. Increasing ALLO enhances GABAergic tonic currents concentration-dependently, but increasing DHEAS reduces these currents. High concentrations of DHEAS (50 μM) reduce GABAergic tonic currents in the presence of ALLO, whereas reduced concentrations of DHEAS (1 μM) further stimulate these currents. These findings demonstrate that decreased concentrations of DHEAS together with increased brain concentrations of ALLO increase GABAergic tonic currents synergistically; suggesting that reduced brain DHEAS could further increase GABAergic tone in human HE.     

Polymer‐in‐“Quasi‐Ionic Liquid” Electrolytes for High‐Voltage Lithium Metal Batteries

Due to the limited oxidation stability (<4 V) of ether oxygen in its polymer structure, polyethylene oxide (PEO)‐based polymer electrolytes are not compatible with high‐voltage (>4 V) cathodes, thus hinder further increases in the energy density of lithium (Li) metal batteries (LMBs). Here, a new type of polymer‐in‐“quasi‐ionic liquid” electrolyte is designed, which reduces the electron density on ethereal oxygens in PEO and ether solvent molecules, induces the formation of stable interfacial layers on both surfaces of the LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) cathode and the Li metal anode in Li||NMC batteries, and results in a capacity retention of 88.4%, 86.7%, and 79.2% after 300 cycles with a charge cutoff voltage of 4.2, 4.3, and 4.4 V for the LMBs, respectively. Therefore, the use of “quasi‐ionic liquids” is a promising approach to design new polymer electrolytes for high‐voltage and high‐specific‐energy LMBs.