Quantitative estimation of the photosynthetic proton binding inside the thylakoids by correlating internal acidification to external alkalinisation and to oxygen evolution in chloroplasts.

The external alkalinisation delta pHe, or the rate of oxygen evolution vO2, of a suspension of envelope-free chlorplasts was correlated with their internal acidification, estimated from the transmembrane delta pHei. Knowing the external buffer value, the concentration of the total protons moved Hi was calculated from the delta pHe, measured with a glass electrode ([Hi] was also obtained from vO2), and the free proton concentration [Hi+] was determined from delta pHei, measured with 9-aminoacridine. This gives a ratio gamma i = theta [Hi]/theta [Hi+], which is independent of the thylakoids internal volume. Within a large pHi range, scanned by varying the light intensity, gamma i was kept reasonably constant; it was hardly sensitive to pHi. This apparent invariability implies a continuous change of the internal buffer value beta i with pHi, since beta i/gamma i = -2.3.....10pHi, a relationship which inlcudes neither the total concentration of protonizable groups [Ai] nor pKi. As gamma i approximately Ki[Ai]/(Ki + [Hi+i]2, to keep gamma i constant when pHi drops, pKi and [Ai] must increase. This may be achieved by a progressive unmasking of anionic functions, initially inaccessible in the membrane. The relative slowness of this process may explain why gamma i calculated from the initial kinetics was sometimes smaller in high than in low light, where it always equalled that measured from the steady-state amplitude at all intensities. A small deficit of [Hi+] deduced from what could have been expected from delta pHe may reflect a limited binding of protons in the membrane itself, about 1 H+ for 30--130 chlorophylls (gamma i could be between 70 and 240, more frequently around 100); these numbers varied depending on the samples, but were constant for a given preparation.     

Electron transport,Photosystem-2 reaction centers and chlorophyll-protein complexes of thylakoids of drought resistant and sensitive Lupin piants

Two genotypes ofLupinus albus L., resistant and susceptible to drought, were subjected to water deficiency for up to two weeks. Such treatment progressively lowered the leaf water content from about 85% to about 60% (water potential from –0.8 to –4.3 MPa). Light-saturation curves of the uncoupled electron transport were analyzed according to a simple kinetic model of separated or connected reversible photoreactions. It gives an extrapolated maximum rate (V_max) and the efficiency for capturing light (I_m, which is the light intensity at V_max/2). For Photosystem 2, V_max and, less markedly, I_m, declined with increasing severity of drought treatment; the artificial donor, diphenylcarbazide, could not restore the activity. One cause of this Photosystem 2 inhibition could be the loss of active Photosystem 2 centers. Indeed, their concentration relative to chlorophyll, estimated by flash-induced reduction of dimethylquinone, was halved by a medium stress. To the extent that it was still not restored by diphenylcarbazide, the site of Photosystem 2 inactivation must have been close to the photochemical trap, after water oxidation and before or at plastoquinone pool. By relating electron transport rate to active centers instead of chlorophyll, no inhibition by drought was detected. Therefore, water stress inactivates specifically Photosystem 2, without impairing a downhill thermal step of electron transport. On the other hand, the decrease of I_m suggests that antennae connected to inactive centers may transfer their excitation energy to active neighbors, which implies that antenna network remains essentially intact. Gel electrophoresis confirmed that the apoproteins of the pigment complexes were well conserved. In conclusion, the inactivation of Photosystem 2 may not be a physical loss of its centers and core antennae but probably reflects protein alterations or conformational changes. These may result from the massive decrease of lipids induced by drought (Meyer et al. 1992, Photosynth. Res. 32: 95–107). Both lupin genotypes behaved similarly but, for a same deficiency, the resistant seemed unexpectedly more sensitive to drought.     

Further investigation on the lateral and transversal proton currents at the thylakoid membrane level by hydrogen-deuterium exchange

Energetically-coupled processes (electron flow, proton uptake and correlated pH gradient) were investigated on envelope-free chloroplasts of lettuce suspended in ¹H₂O or ²H₂O media. Study of the light-intensity and temperature dependencies of these phenomena led to the following observations: 1. At neutral pH, ²H₂O diminishes the transmembrane H⁺ gradient in strong light (chain Photosystem II + Photosystem I) but not in low light; the total H⁺ uptake is increased at all light intensities: the buffering capacity of the inner compartment is increased in heavy water, possibly through enhancement of interactions between membranous titrable groups and the aqueous phase. 2. ²H₂O does not affect the photochemical events of the redox chain, whatever the electron pathway (PSII, PSI or PSII + PSI): only thermal steps are inhibited. The diminution of the apparent quantum yield, sometimes observed, may be ascribed to the dual site of action of the artificial redox carrier (ferricyanide) then used. 3. ²H₂O does not modify the activation energy of the limiting step of the electron flow (PSII + PSI) in uncoupled (44 vs. 47 kJ · mol^?1) or — but less clearly — in coupled, i.e., ‘basal’, state (55 vs. 59 kJ · mol^?1). ²H₂O does not either change the temperature of the phase transition of the membrane (17°C) for the uncoupled flow. However, a low-temperature transition, observed only for the coupled chain, is slightly increased by ²H₂O; this thermal transition is attributed to the freezing of some bound water near the plastoquinone pool. 4. Δp²H is smaller than Δp¹H at all temperatures (PSII + PSI chain). ΔpH is quasi-constant from 0°C to 10°C, then decreases when temperature rises. ²H₂O does not change the activation energy of the dark passive H⁺ efflux, which is almost twice that of the coupled electron flow. The phase transition at low temperature suggests that the proton efflux occurs via two parallel pathways, one temperature-dependent and the other temperature-independent. Except for the increase of the internal buffering capacity, the effects of ²H₂O on the membrane conformation seem limited, as shown by the unchanged activation energies of the electron flow and of the H⁺ leakage. The null activation energy observed at low temperature emphasizes the role of the bound water in these processes; however, the different effects of ²H₂O on the transition temperatures indicate that this bound water has different properties when associated with the translocation sites or with the H⁺ leakage ones. This ‘microcompartmentation’ of the membranes is consistent with the concept of lateral pH heterogeneity we have previously suggested (de Kouchkovsky, Y., and Haraux, F. (1981) Biochem. Biophys. Res. Commun. 99, 205–212). The theoretical computations and the experimental results suggest that in the steady state, the internal pH would be several tenths of a ‘unit’ lower near the plastoquinones than near the H⁺ efflux sites (coupling factors); this difference would be increased when ²H₊ replaces ¹H⁺, owing to the lower mobility of the deuteron. It is concluded that local, and not average, pH (and ΔpH) should be considered for the understanding of the energy transduction processes.     

尿毒症皮肤瘙痒患者采取腹膜透析与血液透析治疗的效果探究

目的：探究尿毒症皮肤瘙瘁患者采取腹膜透析与血液透析治疗的临床效果,并为该病的临床治疗提供经验积累。方法：选取我院肾内科于2005年1月-2012年12月收治的52例尿毒症皮肤瘙痒患者,利用随机数字表法进行分组,分别设为研究组和对照组。其中对照组实施血液透析治疗,而研究组开展腹膜透析治疗。记录两组在治疗前和治疗后第8周末血生化客观指标及皮肤瘙痒程度,并做好对比。结果：两组在治疗前的皮肤瘙痒评分、β2-MG、PTH、p3,BUN、SCr值差异无统计学意义（P〉0．05）;治疗后,研究组皮肤瘙瘁评分为（3．4±0．8）分,对照组为（5．8±0．9）分,差异有统计学意义（P〈0．05）。治疗后,研究组β2-MG、PTH及Ps．均低于对照组,差异有统计学意义（P〈0．05）。结论：尿毒症皮肤瘙痒患者的主要致敏因子为大中分子,采取腹膜透析能够有效清除大分子物质,进而达到瘙痒程度的有效改善。     

Relationships between the photon distribution between the two photosystems, the concentration of system II reaction centers and the intersystem equilibrium constant in Chlorella pyrenoidosa

From Emerson enhancement measurements of O₂ evolution in Chlorella pyrenoidosa, it was possible to establish a relationship between the concentration of photosystem II open reaction centers (E) and the distribution of photons between photosystems I and II [(1 − )/] during steady state. The superposition of lights of two different wavelengths (1 and 2) gives concentrations of E and intermediate between those obtained with light 1 and 2 separately. This relationship extends a previous one based on quantum yield measurements. It has been expressed here by a curve corresponding to a fixed value of the intersystem apparent equilibrium constant (K). Up to 700 nm, K remains equal to 6. Above this wavelength, although the margin of error is rather great, K apparently increases to 12 or more.

The possibility of “spill-over” of light absorbed by System II to System I was studied. There is no probability that this spill-over, if any, exceeds 25% in Chlorella.

The apparent equilibrium constant is decreased by 3(3,4-dichlorophenyl)-1,1-dimethylurea. This is not in favor of the hypothesis of fully independent electron-transfer chains in photosynthesis; it is therefore likely that some communication between those chains exists.     

MicroRNA 10a marks regulatory T cells

MicroRNAs (miRNAs) are crucial for regulatory T cell (Treg) stability and function. We report that microRNA-10a (miR-10a) is expressed in Tregs but not in other T cells including individual thymocyte subsets. Expression profiling in inbred mouse strains demonstrated that non-obese diabetic (NOD) mice with a genetic susceptibility for autoimmune diabetes have lower Treg-specific miR-10a expression than C57BL/6J autoimmune resistant mice. Inhibition of miR-10a expression in vitro leads to reduced FoxP3 expression levels and miR-10a expression is lower in unstable "exFoxP3" T cells. Unstable in vitro TGF-?-induced, iTregs do not express miR-10a unless cultured in the presence of retinoic acid (RA) which has been associated with increased stability of iTreg, suggesting that miR-10a might play a role in stabilizing Treg. However, genetic ablation of miR-10a neither affected the number and phenotype of natural Treg nor the capacity of conventional T cells to induce FoxP3 in response to TGFβ, RA, or a combination of the two. Thus, miR-10a is selectively expressed in Treg but inhibition by antagomiRs or genetic ablation resulted in discordant effects on FoxP3.     

Photochemical restoration of visual responses in blind mice

Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are degenerative blinding diseases caused by the death of rods and cones, leaving the remainder of the visual system intact but largely unable to respond to light. Here, we show that AAQ, a synthetic small molecule photoswitch, can restore light sensitivity to the retina and behavioral responses in?vivo in mouse models of RP, without exogenous gene delivery. Brief application of AAQ bestows prolonged light sensitivity on multiple types of retinal neurons, resulting in synaptically amplified responses and center-surround antagonism in arrays of retinal ganglion cells (RGCs). Intraocular injection of AAQ restores the pupillary light reflex and locomotory light avoidance behavior in mice lacking retinal photoreceptors, indicating reconstitution of light signaling to brain circuits. AAQ and related photoswitch molecules present a potential drug strategy for restoring retinal function in degenerative blinding diseases.     

Energy coupling and ATP synthase

Photosynthesis Research -