Substrate water exchange in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae

The binding affinity of the two substrate–water molecules to the water-oxidizing Mn₄CaO₅ catalyst in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae was studied in the S₂ and S₃ states by the exchange of bound ¹⁶O-substrate against ¹⁸O-labeled water. The rate of this exchange was detected via the membrane-inlet mass spectrometric analysis of flash-induced oxygen evolution. For both redox states a fast and slow phase of water-exchange was resolved at the mixed labeled m/z 34 mass peak: k_f = 52 ± 8 s^− 1 and k_s = 1.9 ± 0.3 s^− 1 in the S₂ state, and k_f = 42 ± 2 s^− 1 and k_slow = 1.2 ± 0.3 s^− 1 in S₃, respectively. Overall these exchange rates are similar to those observed previously with preparations of other organisms. The most remarkable finding is a significantly slower exchange at the fast substrate–water site in the S₂ state, which confirms beyond doubt that both substrate–water molecules are already bound in the S₂ state. This leads to a very small change of the affinity for both the fast and the slowly exchanging substrates during the S₂ → S₃ transition. Implications for recent models for water-oxidation are briefly discussed.     

In vivo photosystem I reduction in thermophilic and mesophilic cyanobacteria: the thermal resistance of the process is limited by factors other than the unfolding of the partners

Photosystem I reduction by plastocyanin and cytochrome c(6) in cyanobacteria has been extensively studied in vitro, but much less information is provided on this process inside the cell. Here, we report an analysis of the electron transfer from both plastocyanin and cytochrome c(6) to photosystem I in intact cells of several cyanobacterial species, including a comparative study of the temperature effect in mesophilic and thermophilic organisms. Our data show that cytochrome c(6) reduces photosystem I by following a reaction mechanism involving complex formation, whereas the copper-protein follows a simpler collisional mechanism. These results contrast with previous kinetic studies in vitro. The effect of temperature on photosystem I reduction leads us to conclude that the thermal resistance of this process is determined by factors other than the proper stability of the protein partners.     

Mycobacterium avium Subspecies Paratuberculosis in the Inflamed Gut Tissues of Patients with Crohn’s Disease in China and its Potential Relationship to the Consumption of Cow’s Milk: A Preliminary Study

Summary Mycobacterium avium subspecies paratuberculosis infection in domestic livestock is widespread in many countries throughout the world. Studies in Europe and the USA show that M. avium subspecies paratuberculosis can be cultured from retail pasteurized cow’s milk and that these organisms are being transmitted to humans by this route. Most people with chronic inflammation of the intestine of the Crohn’s disease type are infected with these chronic enteric pathogens. The production and consumption of cow’s milk has increased in China and so also has the incidence of Crohn’s disease. The present preliminary investigation was carried out to determine whether M. avium subspecies paratuberculosis is present in the intestinal tissues of Chinese patients with Crohn’s disease who have never left China. Archival paraffin-embedded surgical pathology blocks from patients having surgery for Crohn’s disease (CD) or for cancer (nIBD) in China were studied. M. avium subspecies paratuberculosis was detected by nested IS900 PCR with Southern blotting and amplicon sequencing. The intestinal tissues of 9 of 13 (69.2%) CD patients and 2 of 14 (14.3%) nIBD patients were IS900 PCR positive (P = 0.0063; odds ratio = 13.5). These initial studies suggest that people in China are exposed to M. avium subspecies paratuberculosis and that as in other countries, the infection is significantly associated with Crohn’s disease. M. avium subspecies paratuberculosis in dairy herds and retail milk in China needs to be investigated.     

快速干燥对黄皮胚轴贮藏寿命及抗氧化酶活性的影响

以黄皮种子离体胚轴为材料 ,研究了快速干燥对胚轴贮藏寿命的影响及与抗氧化酶活性的关系。未经脱水的胚轴在 15℃贮藏 12 8d仍具有较高的存活率和活力指数。快速脱水 1.5和 3.0h后胚轴的存活率和活力指数并未因脱水而下降 ,但它们在 15℃贮藏的寿命分别只有 8和 2d。未经脱水胚轴的抗氧化酶(SOD、POD、CAT)活性在贮藏过程中能较好地保持 ,但经快速脱水后其抗氧化酶活性在贮藏过程中则迅速下降 ,脱水时间越长 ,酶活性在贮藏过程中的下降就越快。     

Simple procedures for analyzing and purifying methylene green

Abstract

Methylene green is a versatile dye that can be used in a wide range of technical applications, most of which require the dye to be pure. Because commercial lots of methylene green are known to be heterogeneous, we report a thin layer chromatographic method for checking purity. We also describe a simple and effective flash chromatographic purification procedure for subsequent purification. The identity and purity of the dye can be checked easily using UV-visible absorption spectrum measurements or by more sophisticated procedures if necessary.     

Flash Infrared Annealing for Antisolvent‐Free Highly Efficient Perovskite Solar Cells

Organic–inorganic perovskites have demonstrated an impressive potential for the design of the next generation of solar cells. Perovskite solar cells (PSCs) are currently considered for scaling up and commercialization. Many of the lab‐scale preparation methods are however difficult to scale up or are environmentally unfriendly. The highest efficient PSCs are currently prepared using the antisolvent method, which utilizes a significant amount of an organic solvent to induce perovskite crystallization in a thin film. An antisolvent‐free method is developed in this work using flash infrared annealing (FIRA) to prepare methylammonium lead iodide (MAPbI₃) PSCs with a record stabilized power conversion efficiency of 18.3%. With an irradiation time of fewer than 2 s, FIRA enables the coating of glass and plastic substrates with pinhole‐free perovskite films that exhibit micrometer‐size crystalline domains. This work discusses the FIRA‐induced crystallization mechanism and unveils the main parameters controlling the film morphology. The replacement of the antisolvent method and the larger crystalline domains resulting from flash annealing make FIRA a highly promising method for the scale‐up of PSC manufacture.     

Regulation of Ca2+ Release by InsP3 in Single Guinea Pig Hepatocytes and Rat Purkinje Neurons

The repetitive spiking of free cytosolic [Ca²⁺] ([Ca²⁺]_i) during hormonal activation of hepatocytes depends on the activation and subsequent inactivation of InsP₃-evoked Ca²⁺ release. The kinetics of both processes were studied with flash photolytic release of InsP₃ and time resolved measurements of [Ca²⁺]_i in single cells. InsP₃ evoked Ca²⁺ flux into the cytosol was measured as d[Ca²⁺]_i/dt, and the kinetics of Ca²⁺ release compared between hepatocytes and cerebellar Purkinje neurons. In hepatocytes release occurs at InsP₃ concentrations greater than 0.1–0.2 μM. A comparison with photolytic release of metabolically stable 5-thio-InsP₃ suggests that metabolism of InsP₃ is important in determining the minimal concentration needed to produce Ca²⁺ release. A distinct latency or delay of several hundred milliseconds after release of low InsP₃ concentrations decreased to a minimum of 20–30 ms at high concentrations and is reduced to zero by prior increase of [Ca²⁺]_i, suggesting a cooperative action of Ca²⁺ in InsP₃ receptor activation. InsP₃-evoked flux and peak [Ca²⁺]_i increased with InsP₃ concentration up to 5–10 μM, with large variation from cell to cell at each InsP₃ concentration. The duration of InsP₃-evoked flux, measured as 10–90% risetime, showed a good reciprocal correlation with d[Ca²⁺]_i/dt and much less cell to cell variation than the dependence of flux on InsP₃ concentration, suggesting that the rate of termination of the Ca²⁺ flux depends on the free Ca²⁺ flux itself. Comparing this data between hepatocytes and Purkinje neurons shows a similar reciprocal correlation for both, in hepatocytes in the range of low Ca²⁺ flux, up to 50 μM · s⁻¹ and in Purkinje neurons at high flux up to 1,400 μM · s⁻¹. Experiments in which [Ca²⁺]_i was controlled at resting or elevated levels support a mechanism in which InsP₃-evoked Ca²⁺ flux is inhibited by Ca²⁺ inactivation of closed receptor/channels due to Ca²⁺ accumulation local to the release sites. Hepatocytes have a much smaller, more prolonged InsP₃-evoked Ca²⁺ flux than Purkinje neurons. Evidence suggests that these differences in kinetics can be explained by the much lower InsP₃ receptor density in hepatocytes than Purkinje neurons, rather than differences in receptor isoform, and, more generally, that high InsP₃ receptor density promotes fast rising, rapidly inactivating InsP₃-evoked [Ca²⁺]_i transients.     

Alternative Cyanide-sensitive Oxidase Interacting with Photosynthesis in Synechocystis PCC6803. Ancestor of the Terminal Oxidase of Chlororespiration?

Influence of respiration on photosynthesis in Synechocystis PCC6803 was studied by measuring the redox transients of cytochrome f (cyt f) upon excitation of the cells with repetitive single turnover flashes. Upon the addition of KCN the flash-induced oxidation of cyt f was increased and the rereduction of cyt f+ was accelerated. Dependence of these effects on the concentration of KCN clearly demonstrated the existence of two cyanide-sensitive oxidases interacting with photosynthesis: cyt aa3, which was sensitive to low concentrations of cyanide, and an alternative oxidase, which could be suppressed by using 1 mM KCN. The interaction between the photosynthetic and the respiratory electron transport chains was regulated mainly by the activity of the alternative cyanide-sensitive oxidase. The oxidative pathway involving the alternative cyanide-sensitive oxidase was insensitive to salicyl hydroxamic acid and azide. The close resemblance of the inhibition pattern reported here and that described for chlororespiration in algae and higher plants strongly suggest that an oxidase of the same type as the alternative cyanide-sensitive oxidase of cyanobacteria functions as a terminal oxidase in chloroplasts.     

Electrostatic forces involved in orienting Anabaena ferredoxin during binding to Anabaena ferredoxin:NADP+ reductase: site-specific mutagenesis, transient kinetic measurements, and electrostatic surface potentials.

Transient absorbance measurements following laser flash photolysis have been used to measure the rate constants for electron transfer (et) from reduced Anabaena ferredoxin (Fd) to wild-type and seven site-specific charge-reversal mutants of Anabaena ferredoxin:NADP+ reductase (FNR). These mutations have been designed to probe the importance of specific positively charged amino acid residues on the surface of the FNR molecule near the exposed edge of the FAD cofactor in the protein-protein interaction during et with Fd. The mutant proteins fall into two groups: overall, the K75E, R16E, and K72E mutants are most severely impaired in et, and the K138E, R264E, K290E, and K294E mutants are impaired to a lesser extent, although the degree of impairment varies with ionic strength. Binding constants for complex formation between the oxidized proteins and for the transient et complexes show that the severity of the alterations in et kinetics for the mutants correlate with decreased stabilities of the protein-protein complexes. Those mutated residues, which show the largest effects, are located in a region of the protein in which positive charge predominates, and charge reversals have large effects on the calculated local surface electrostatic potential. In contrast, K138, R264, K290, and K294 are located within or close to regions of intense negative potential, and therefore the introduction of additional negative charges have considerably smaller effects on the calculated surface potential. We attribute the relative changes in et kinetics and complex binding constants for these mutants to these characteristics of the surface charge distribution in FNR and conclude that the positively charged region of the FNR surface located in the vicinity of K75, R16, and K72 is especially important in the binding and orientation of Fd during electron transfer.