Local anesthetics-induced inhibition of chloroplast electron transport

The effects of local anesthetics on photosynthetic activity of pea chloroplasts were investigated in order to elucidate the role of Ca2+ in photosynthetic electron transport. Dibucaine, benzocaine and tetracaine were found to inhibit the O2-evolving activity. The inhibitory effect decreases in the order dibucaine greater than benzocaine greater than tetracaine greater than trimecaine similarly as does the potency to inhibit propagation of excitation in nerve fibre. As demonstrated in experiments with artificial donors and acceptors, the site of inhibition is the water-splitting site of PSII. The inhibitory power of the anesthetics grows with increasing ionic strength of the incubating mixture (by adding NaCl or MgCl2) and with pH; this is explained by occurrence of the neutral form of amine. At low concentrations the charged anesthetic acts as a protonofore; however, the inactivation of water splitting is not due to the protonophoric effect. The incubation is followed by the disappearance of ESR signal IIs. The role of Ca2+ and Ca2+-binding protein in PSII electron transport and its localization are discussed.     

Clear-cutting impacts nutrient,carbon and water exchange parameters in woody plants in an east Fennoscandian pine forest

Plant and Soil - Clear-cut logging currently is a key factor transforming forest communities in many boreal regions. The dynamics of biogeochemical processes taking place in clear-cuts makes them a...     

Converging Modalities Ground Abstract Categories: The Case of Politics

Three studies are reported examining the grounding of abstract concepts across two modalities (visual and auditory) and their symbolic representation. A comparison of the outcomes across these studies reveals that the symbolic representation of political concepts and their visual and auditory modalities is convergent. In other words, the spatial relationships between specific instances of the political categories are highly overlapping across the symbolic, visual and auditory modalities. These findings suggest that abstract categories display redundancy across modal and amodal representations, and are multimodal.     

Mossbauer spectroscopic study of functional thermal destruction of iron--sulfur proteins in membranes of thermophilic cyanobacteria synechococcus elongatus

A mathematical model of the Mossbauer spectrum (80K) of native membranes of Synechococcus elongatus was constructed on the basis of values of the quadruple splitting (Delta) and the isomeric shift (delta) of the iron-containing components of the photosynthetic apparatus obtained from the literature. Thermally induced changes in the intensity of the spectral components of membranes and isolated preparations of photosystem (PS) I were studied using this model. It was shown that exposure of membranes to 70-80 degrees C causes a decrease in the intensity of the components related to the FX, FA, and FB centers and surface-located ferredoxins of PS I, an increase in the intensity of the doublets of oxidized iron clusters that are nonspecifically absorbed by the membranes, and formation of a new doublet. Spectral parameters of this doublet (Delta = 3.10 mm/sec and delta = 1.40 mm/sec) are typical of inorganic hydrated forms of reduced iron. Heating of PS I preparations also causes a decrease in the intensity of doublets of the FX, FA, and FB centers and an increase in the intensity of doublets of nonspecifically bound oxidized iron. However, this does not cause formation of inorganic reduced iron. Comparison between the intensities of the Mossbauer spectral components in intact and heated samples suggests that the main source of reduced iron in membranes is surface-located ferredoxins. Nonspecifically bound oxidized iron is formed at the expense of the FX, FA, and FB centers. Disappearance of spectral components associated with ferredoxins and accumulation of reduced iron in membranes occur within the temperature range critical for inhibition of electron transport through PS I to oxygen. These findings suggest that the thermally induced processes of accumulation of reduced iron and inhibition of electron transport in PS I in membranes of thermophilic cyanobacteria are interrelated and caused mainly by degradation of the Fe--S centers of ferredoxins. The possible role of reduced iron accumulation in the degradation of the photosynthetic apparatus induced by heat and other extreme physical and chemical factors is discussed.     

Errantiviruses of Drosophila

The view on Drosophila long terminal repeat (LTR) retrotransposons, which have three reading frames, as endogenous retroviruses or errantiviruses (ERVs, according to the latest ICTV nomenclature) is discussed. Data on the biology of ERVs and the mechanisms of their involvement in genetic instability of Drosophila are considered.     

Blocking of electron donation by Mn(II) to Y(Z*) following incubation of Mn-depleted photosystem II membranes with Fe(II) in the light

The donation of electrons by Mn(II) and Fe(II) to Y(Z*) through the high-affinity (HA(Z)) site in Mn-depleted photosystem II (PSII) membranes has been studied by flash-probe fluorescence yield measurements. Mn(II) and Fe(II) donate electrons to Y(Z*) with about the same efficiency, saturating this reaction at the same concentration (ca. 5 microM). However, following a short incubation of the membranes with 5 microM Fe(II), but not with Mn(II) in room light, added Mn(II) or Fe(II) can no longer be photooxidized by Y(Z)(*). This blocking effect is caused by specifically bound, photooxidized Fe [> or =Fe(III)] and is accompanied by a delay in the fluorescence yield decay kinetics attributed to the slowing down of the charge recombination rate between Q(a-) and Y(Z*). Exogenously added Fe(III), on the other hand, does not donate electrons to Y(Z*), does not block the donation of electrons by added Mn(II) and Fe(II), and does not change the kinetics of the decay of the fluorescence yield. These results demonstrate that the light-dependent oxidation of Fe(II) by Y(Z*) creates an Fe species that binds at the HA(Z) site and causes the blocking effect. The pH dependence of Mn(II) electron donation to Y(Z*) via the HA(Z) site and of the Fe-blocking effect is different. These results, together with sequence homologies between the C-terminal ends of the D1 and D2 polypeptides of the PSII reaction center and several diiron-oxo enzymes, suggest the involvement of two or perhaps more (to an upper limit of four to five) bound iron cations per reaction center of PSII in the blocking effect. Similarities in the interaction of Fe(II) and Mn(II) with the HA(Z) Mn site of PSII during the initial steps of the photoactivation process are discussed. The Fe-blocking effect was also used to investigate the relationship between the HA(Z) Mn site and the HA sites on PSII for diphenylcarbazide (DPC) and NH2OH oxidation. Blocking of the HA(Z) site with specifically bound Fe leads to the total inhibition of electron donation to Y(Z*) by DPC. Since DPC and Mn(II) donation to PSII is noncompetitive [Preston, C., and Seibert, M. (1991) Biochemistry 30, 9615-9624], the Fe bound to the HA(Z) site can also block the DPC donation site. On the other hand, electron donation by NH2OH to PSII still occurs in Fe-blocked membranes. Since hydroxylamine does not reduce the Fe [> or =Fe(III)] specifically bound to the HA(Z) site, NH2OH must donate to Y(Z*) through its own site or directly to P680+.     

Structural transition in peptide nanotubes

Phase transitions in organic and inorganic materials are well-studied classical phenomena, where a change in the crystal space group symmetry induces a wide variation of physical properties, permitted by the crystalline symmetry in each phase. Here we observe a conformational induced transition in bioinspired peptide nanotubes (PNTs). We found that the PNTs change their original molecular assembly from a linear peptide conformation to a cyclic one, followed by a change of the nanocrystalline structure from a noncentrosymmetric hexagonal space group to a centrosymmetric orthorhombic space group. The observed transition is irreversible and induces a profound variation in the PNTs properties, from the microscopic to the macroscopic level. In this context, we follow the unique changes in the molecular, morphological, piezoelectric, second harmonic generation, and wettability properties of the PNTs.     

Mossbauer spectroscopy of cells of cyanobacteria Synechocystis sp. PCC 6803 devoid of photosystem I and containing inactive phycobilisomes]

Mossbauer spectra of the psaAB mutant of Synechocystis sp. PPC 6803 devoid of photosystem I grown in a 57Fe-containing medium were measured. The spectrum is a broadened doublet whose size (about 20%) and parameters (isomeric shift delta = 0.3 mm/s and quadrupole splitting delta = 0.8 mm/s) suggest the presence of abundant nanoclusters of Fe3+ oxides in a superparamagnetic state tightly bound to the membrane. Treatment of cells with EDTA was accompanied by a substantial (tenfold) decrease in the amount of iron nonspecifically bound to the membrane and the appearance of Fe2+ localized, probably, inside cells and/or cell membranes. In addition, the spectrum of washed cells exhibited superfine magnetic splitting due to iron oxide clusters greater in size than nanoclusters present in the membrane prior to EDTA treatment.     

A novel approach to determine water content in DMSO for a compound collection repository

The quality of a corporate compound collection can be significantly affected by a complex combination of storage and operational processing factors. Water content in DMSO solutions is one factor that is of great interest as it can affect solubility, degradation, and freeze-thaw cycle parameters. To the authors' knowledge, this is the first report of using near-infrared (NIR) spectroscopy to assess water content in DMSO compound stock solutions within the common storage vessel format of polypropylene microtubes. The precision and accuracy of the NIR technique was benchmarked against a Karl Fisher titration method, and a correlation coefficient was determined to be 0.985 over a range of 1% to 10% water in DMSO by weight. The advantages of the NIR technique include accuracy, precision, speed, nondestructiveness, and the capability of assessing compounds under in situ storage conditions within microtubes. In this report, the authors demonstrate the accuracy and precision of using NIR to assess water content in DMSO solutions and present a case study to demonstrate the utility of the technique to aid in assessing a pharmaceutical compound collection.     

Effects of acute footshock stress on antioxidant enzyme activities in the adolescent rat brain

In a previous study we demonstrated that acute footshock stress increased glutathione peroxidase activity in the prefrontal cortex and striatum of adult male rats. Adolescents may respond differently to stress as life stressors may be greater than at other ages. The present study examined the effects of the acute footshock stress on superoxide dismutase (SOD) and glutathione peroxidase (GPx) enzyme activities and thiobarbituric acid reactive substances (TBARS) levels in adolescent male and female rat brains. We demonstrated that acute footshock stress increased SOD activity in the prefrontal cortex, and increased GPx activity in the hippocampus in female rats. In males, acute footshock stress increased GPx activity in the prefrontal cortex and hippocampus. Footshock stress did not change TBARS levels. These results indicate a strong role of gender in the response of adolescent subjects to various aspects of stress.