Identification of the Chromophores Involved in Aggregation-dependent Energy Quenching of the Monomeric Photosystem II Antenna Protein Lhcb5

Non-photochemical quenching (NPQ) of excess absorbed light energy is a fundamental process that regulates photosynthetic light harvesting in higher plants. Among several proposed NPQ mechanisms, aggregation-dependent quenching (ADQ) and charge transfer quenching have received the most attention. In vitro spectroscopic features of both mechanisms correlate with very similar signals detected in more intact systems and in vivo, where full NPQ can be observed. A major difference between the models is the proposed quenching site, which is predominantly the major trimeric light-harvesting complex II in ADQ and exclusively monomeric Lhcb proteins in charge transfer quenching. Here, we studied ADQ in both monomeric and trimeric Lhcb proteins, investigating the activities of each antenna subunit and their dependence on zeaxanthin, a major modulator of NPQ in vivo. We found that monomeric Lhcb proteins undergo stronger quenching than light-harvesting complex II during aggregation and that this is enhanced by binding to zeaxanthin, as occurs during NPQ in vivo. Finally, the analysis of Lhcb5 mutants showed that chlorophyll 612 and 613, in close contact with lutein bound at site L1, are important facilitators of ADQ.     

Austrocolorins A1 and B1: atropisomeric 10,10'-linked dihydroanthracenones from an Australian Dermocybe sp

The atropisomeric austrocolorins A(1) (7) and B(1) (8), new members of the rare tricolorin class of 10,10'-coupled dihydroanthracenones, are isolated from an indigenous Australian toadstool belonging to the subgenus Dermocybe of Cortinarius, and their structure and absolute central and axial configuration is deduced from the spectroscopic data, and confirmed by chemical degradation and chiral HPLC analysis.     

Photosynthetic energy conversion under extreme conditions--I: important role of lipids as structural modulators and energy sink under N-limited growth in Antarctic sea ice diatoms

The availability of dissolved nutrients such as nitrate under extreme low temperatures is a strong determinant in the development and growth of ice diatoms. Consequently we investigated regulation of photosynthesis in a mixed culture of three diatom species, which grew in chemostats at -1 degrees C, 15 micromol photons m(-2) s(-1) under N-limitation. When nitrogen is limiting, pigment-protein complexes are one of the most affected structures under low-light conditions. The loss of integral polar thylakoid components destabilized the bilayer structure of the membrane with consequences for lipid composition and the degree of fatty acid desaturation. N-Limitation caused a decrease in monogalactosydiacylglycerol (MGDG) and a simultaneous increase in bilayer forming digalactosyldiacylglycerol (DGDG). Their ratio MGDG:DGDG decreased from 3.4 +/- 0.1 to 1.1 +/- 0.4, while 20:5 n-3 fatty acids of chloroplast related phospholipid classes such as phosphatidylglycerol (PG) increased under N-limitation. These data reveal that lipids are important components, required to sustain membrane structure under a deficiency of integral membrane bound proteins and pigments. Nonetheless, energy conversion at photosystem II is still affected by N-limitation despite this structural regulation. Photosynthetic quantum yield (F(v)/F(m)) and electron transport rates decreased under N-limitation caused by an increasing amount of electron acceptors (second stable electron acceptor = Q(B)) which had slower reoxidation kinetics. The energy surplus under these conditions is stored in triacylglycerols, the main energy sink in Antarctic sea ice diatoms under N-limitation.     

Chemical characterization and toxicity evaluation of fungal pigments for potential application in food,phamarceutical and agricultural industries

Concerns associated with the use of synthetic colourants backs the demand for natural colourants. Thus, the current study aimed at characterizing crude fungal pigments produced by Penicillium multicolour, P. canescens, Talaromyces verruculosus, Fusarium solani and P. herquie. This included their antioxidant and antimicrobial properties together with acute toxicity evaluation on zebrafish embryos. The identification of pigment compounds was achieved through MS and IR data. The study demonstrated a substantial radical scavenging activity of extracts ranging from 65.49 to 74.46%, close to that of ascorbic acid (89.21%). Penicillium canescens and F. solani exhibited a strong antimicrobial activity against Escherichia coli and Enterococcus aerogenes and Salmonella typhi, Staphylococcus aureus and Bacillus cereus at MIC values ranging from 1.5 to 2.5 mg/mL. However, some levels of toxicity were observed for all extracts at a concentration range of 3–5 mg/mL. Pigment by P. multicolour, T. verruculosus and F. solani were tentatively identified through IR and MS data as sclerotiorin (yellow), rubropunctamine (red) and bostrycoidin (red). In conclusion, the study demonstrates a market potential of filamentous fungi pigments due to their antioxidant, antimicrobial activities, and prominent colours. Although there are some toxicity concerns, further tests must be done using molecular docking, albino mice and cell linings.     

红曲色素的两种新结构

从中国科学院微生物研究所保藏红曲菌中,筛选得到一株高产红色素的红曲菌菌株(AS.3.4617)。经鉴定属于红色红曲菌(Monascus anka Sato).通过有机溶剂的萃取和两次硅胶柱层析,从该菌株中分离得到两种色素样品,高压液相色谱测定为纯色素样品。通过元素组成分析,核磁共振谱,快离子轰击,质谱和高分辨质谱分析确定,这两种色素与已知的六种红曲菌色素不同,为新发现的红曲菌色素,它们可能的分子式为:C_(25)H_(31)O_5N和C_(23)H_(27)O_5N。     

Repeated-batch production of pigments by immobilised Monascus purpureus

Extracellular pigment production by immobilised Monascus purpureus C322 has been studied in repeated-batch processes using different immobilising carriers such as Ca-alginate, polyurethane sponge, active carbon and pearlite. With Ca-alginate, pigment production was maximum (30.5 UA₄₇₀ as process mean production, three batches) while the cell leakage was negligible (0.4 g l⁻¹ free biomass) and the bead mechanical stability good; with this carrier, an extended repeated-batch fermentation (nine batches, 55 days) was carried out: the process pigment productivity was 3.87 UA₄₇₀ day⁻¹.     

5-Azacytidine decreases fragmentation of nuclear DNA and pigment formation in first leaf cells of barley seedlings

Realization of programmed cell death in senescence represents an activation/inactivation of the respective gene. Enzymatic methylation of nuclear DNA with the creation of 5methylcytosine is one of the mechanisms, which can regulate gene activity in animal and plant cells. 5Azacytidine (5azaC) acts as an inhibitor of DNA methylation, and induces expression of a range of some genes including genes responsible for senescence. Fragmentation of nuclear DNA is one of the hallmarks of programmed cell death in apoptosis pathway in plant cells. The influence of 5azaC (100 microg/ml) on nuclear DNS amount and its fragmentation in the first leaf cells of barley was studied. It was shown that in the first leaf cells of barley seedlings there is an apoptosis pathway of programmed cell death. It was also observed that nuclear DNA fragmentation under the 5azaC influence is strongly inhibited, and the DNA amount in the first leaf increases. Synthesis and destruction of chlorophyll also play a significant role in programmed cell death in plants. It was shown that under the 5azaC influence, the absorption spectrum of a pigment does not change in leaves and coleoptiles in the light, whereas in the dark condition, these pigments are not created under the 5azaC influence.     

Mutation Analysis of Violaxanthin De-epoxidase Identifies Substrate-binding Sites and Residues Involved in Catalysis

Plants are able to deal with variable environmental conditions; when exposed to strong illumination, they safely dissipate excess energy as heat and increase their capacity for scavenging reacting oxygen species. Both these protection mechanisms involve activation of the xanthophyll cycle, in which the carotenoid violaxanthin is converted to zeaxanthin by violaxanthin de-epoxidase, using ascorbate as the source of reducing power. In this work, following determination of the three-dimensional structure of the violaxanthin de-epoxidase catalytic domain, we identified the putative binding sites for violaxanthin and ascorbate by in silico docking. Amino acid residues lying in close contact with the two substrates were analyzed for their involvement in the catalytic mechanism. Experimental results supported the proposed substrate-binding sites and point to two residues, Asp-177 and Tyr-198, which are suggested to participate in the catalytic mechanism, based on complete loss of activity in mutant proteins. The role of other residues and the mechanistic similarity to aspartic proteases and epoxide hydrolases are discussed.     

A Reaction Center-dependent Photoprotection Mechanism in a Highly Robust Photosystem II from an Extremophilic Red Alga,Cyanidioschyzon merolae

Members of the rhodophytan order Cyanidiales are unique among phototrophs in their ability to live in extremely low pH levels and moderately high temperatures. The photosynthetic apparatus of the red alga Cyanidioschyzon merolae represents an intermediate type between cyanobacteria and higher plants, suggesting that this alga may provide the evolutionary link between prokaryotic and eukaryotic phototrophs. Although we now have a detailed structural model of photosystem II (PSII) from cyanobacteria at an atomic resolution, no corresponding structure of the eukaryotic PSII complex has been published to date. Here we report the isolation and characterization of a highly active and robust dimeric PSII complex from C. merolae. We show that this complex is highly stable across a range of extreme light, temperature, and pH conditions. By measuring fluorescence quenching properties of the isolated C. merolae PSII complex, we provide the first direct evidence of pH-dependent non-photochemical quenching in the red algal PSII reaction center. This type of quenching, together with high zeaxanthin content, appears to underlie photoprotection mechanisms that are efficiently employed by this robust natural water-splitting complex under excess irradiance. In order to provide structural details of this eukaryotic form of PSII, we have employed electron microscopy and single particle analyses to obtain a 17 Å map of the C. merolae PSII dimer in which we locate the position of the protein mass corresponding to the additional extrinsic protein stabilizing the oxygen-evolving complex, PsbQ′. We conclude that this lumenal subunit is present in the vicinity of the CP43 protein, close to the membrane plane.     

金花菌黄色素的稳定性及其抗氧化活性研究

【目的】评价茯砖茶金花菌黄色素的稳定性和抗氧化性能。【方法】以色素保存率为指标, 研究温度、光照和pH对黄色素稳定性的影响。并对还原能力、DPPH·清除能力和H2O2诱导的红细胞溶血抑制能力进行测定, 考察黄色素的抗氧化性能。【结果】该色素在低温下保存7 d保存率高于98.88%, 温度升高, 保存率降低; 光照尤其是太阳光对其稳定性影响较大; 黄色素在pH 2?10较稳定, pH 12时色素保存率仅为46.22%。低浓度黄色素具有明显高于维生素E (VE)的还原能力、DPPH·清除率和溶血抑制率, 其中DPPH·的EC50低于50 mg/L。【结论】金花菌黄色素对热、酸和弱碱较稳定, 对强碱和太阳光极不稳定, 并有优良的抗氧化能力, 研究和开发前景良好。