The photoreaction center of Rhodospirillum rubrum mutant strain F24.1

Rhodospirillum rubrum strain F24.1 is a spontaneous revertant of nonphototrophic mutant F24 derived from wild-type strain S1. Strain F24 shows no detectable photochemical activity and contains, at most, traces of the photoreaction center polypeptides. Strain F24.1 has a phototrophic growth rate close to that of the wild-type strain (Picorel, R., del Valle-Tascón, S. and Ramírez, J.M. (1977) Arch. Biophys. Biochem. 181, 665–670) but shows little photochemical activity. Light-induced absorbance changes in the near-infrared, photoinduced EPR signals and ferricyanide-elicited absorbance changes indicate that strain F24.1 has a photoreaction center content of 7–8% as compared to strain S1. Polyacrylamide gel electrophoresis of isolated F24.1 chromatophores shows the photoreaction center polypeptides to be present in amounts compatible with this value. Photoreaction center was prepared from strain F24.1 and showed no detectable difference with that of strain S1. It is concluded that strain F24.1 photosynthesis is due entirely to its residual 7–8% of typical photoreaction center.     

Inhibition of Photosystem II by formate. Possible evidence for a direct role of bicarbonate in photosynthetic oxygen evolution

In broken chloroplasts the presence of 100 mM sodium formate at pH 8.2 will specifically lengthen the Photosystem II relaxation times of the reactions S′₂ → S₃ and S′₃ → S₀. Rates of reactions S′₀ → S₁ and S′₁ → S₂ remain unaffected. Evidence is presented which indicates the discrimination among S-states by formate cannot be attributed to a block imposed on the reducing side of Photosystem II. The results are interpreted in context of the known interaction of formate and CO₂ which is bound to the Photosystem II reaction center complex. It is proposed that those S-state transitions which show extended relaxation times in the presence of formate must result in the momentary release and rebinding of CO₂. Furthermore since formate is acting on the oxygen-evolving side of Photosystem II, it would seem that CO₂ is released in reactions that occur there. A chemical model of oxygen evolution is presented. It is based on the hypothesis that hydrated CO₂ is the immediate source of photosynthetically evolved oxygen and explains why, under certain conditions formate slows only the S-state transitions S′₂ → S₃ and S′₃ → S₀.     

The photosynthetic electron transfer chain of Chromatium vinosum chromatophores flash-induced cytochrome b reduction

Reduction of a cytochrome b following excitation by a single, short, near-saturating light flash has been demonstrated in Chromatium vinosum chromatophores. The extent of reduction is increased by addition of antimycin. The cytochrome has an α-band maximum at 562 nm in the presence of antimycin.The cytochrome b reduction is most readily observed in the presence of antimycin at high redox potential when cytochrome c-555 is oxidised before excitation. Under these conditions the half-time for reduction is about 20 ms, and the extent is about 0.5 mol of cytochrome b reduced per mol of reaction center oxidised. This extent of reduction is observed on the first flash-excitation from the dark-adapted state, and there was no indication that the reaction center quinone acceptor complex acted as a two-electron accumulating system. With cytochrome c-555 reduced before excitation, the extent of cytochrome b reduction is approximately halved. The factors which result in substoichiometric cytochrome b reduction are not yet understood.Agents which appear to inhibit primary acceptor oxidation by the secondary acceptor (UHDBT, PHDBT, DDAQQ, HOQNO, o-phenanthroline), inhibit reduction of the cytochrome b. DBMIB inhibits cytochrome b reduction but does not appear to inhibit primary acceptor oxidation.These observations confirm that a cytochrome b receives electrons delivered from the primary acceptor complex, and indicate that the photoreduced cytochrome b is reoxidised via an antimycin-sensitive pathway.     

Relative activities of linear and cyclic electron flows during chloroplast CO2-fixation

Evolution of oxygen and turnover of cytochromes b-563 and ? were measured upon illumination of isolated intact spinach chloroplasts with a series of flashes. The flash yield of cytochrome ? oxidation approximated the sum of the yields of cytochrome b-563 reduction and electron transfer through Photosystem II, regardless of whether HCO^?₃, 3-phosphoglycerate or O₂ served as the terminal electron acceptor. No absorbance contribution from cytochrome b-559 was discerned within the time range studied. Some pseudocyclic electron flow occurred when both HCO^?₃ and 3-phosphoglycerate were omitted, and possibly also during induction of photosynthesis; however, the flash yield data suggest that O₂ is not reduced at a significant rate during steady state photosynthesis. The maximum rate of cytochrome ? turnover (1000 μequiv./mg chlorophyll per h) was adequate to support the highest rates of photosynthesis observed in isolated chloroplasts.These results agree with the concept that cytochrome ? is a component both of the linear and cyclic pathways whereas cytochrome b-563 functions only in the cyclic pathway. NH₄Cl decreased the half time of cytochrome b-563 oxidation from 11.6 to 8.2 ms and decreased the half time of cytochrome ? reduction from 7.2 to 2.8 ms. The cyclic and linear pathways thus seem to be jointly regulated by a transthylakoid H⁺ gradient through a common control point on the reducing side of cytochrome ?. Cyclic turnover also increased during the induction phase of photosynthesis, when linear throughput is limited by the rate of utilization of NADPH. The slow rise in the P-518 transient correlated with increased cyclic activity under the above conditions.It is proposed that flexibility in the utilization of linear and cyclic pathways allows the chloroplast to generate ATP and NADPH in ratios appropriate to varying needs.     

Delayed fluorescence from Rhodopseudomonas viridis following single flashes

Delayed fluorescence from Rhodopseudomonas viridis membrane fragments has been studied using a phosphoroscope employing single, short actinic flashes, under conditions of controlled redox potential and temperature. The emission spectrum shows that delayed fluorescence is emitted by the bulk, antenna bacteriochlorophyll. The energy for delayed fluorescence, however, must be stored in a reaction-center complex including the photooxidized form (P⁺) of the primary electron-donor (P) and the photoreduced form (X^?) of the primary electron-acceptor. This is shown by the following observations: (1) Delayed luminescence is quenched (a) at low redox potentials which allow cytochromes to reduce P⁺ rapidly after the flash, (b) at higher redox potentials which, by oxidizing P chemically, prevent the photochemical formation of P⁺X^?, and (c) upon transfer of an electron from X^? to a secondary acceptor, Y. (2) Under conditions that prevent the reduction of P⁺ by cytochromes and the oxidation of X^? by Y, the decay kinetics of delayed fluorescence are identical with those of P⁺X^?, as measured from optical absorbance changes.The main decay route for P⁺X^? under these conditions has a rate-constant of approximately 10³ s^?1. In contrast, a comparison of the intensities of delayed and prompt fluorescence indicates that the process in which P⁺X^? returns energy to the bulk bacteriochlorophyll has a rate-constant of 3.7 s^?1, at 295 °K and pH 7.8. The decay kinetics of P⁺X^? and delayed fluorescence change little with temperature, whereas the intensity of delayed fluorescence increases with increasing temperature, having an activation energy of 12.5 kcal · mol^?1. We conclude that the main decay route involves tunneling of an electron from X^? to P⁺, without the promotion of P to an excited state. Delayed fluorescence requires such a promotion, followed by transfer of energy to the bulk bacteriochlorophyll, and this combination of events is rare. The activation energy, taken with potentiometric data, indicates that the photochemical conversion of PX to P⁺X^? results in increases of both the energy and the entropy of the system, by 16.6 kcal · mol^?1 and 8.8 cal · mol^?1 · deg^?1. The intensity of delayed fluorescence depends strongly on the pH; the origin of this effect remains unclear.     

Chemical composition of fresh and composted urban waste

Chemical, spectroscopic (IR and NMR), and molecular characteristics of humus extracted from urban waste before and after compositing are reported. The main differences are in the contents of acidic groups and straight aliphatic chains which diminish in the composted material. In comparing humus characteristics of composted urban waste and soils, the only real difference was found in the elution curves on Sephadex G-100, where the ratio of 100,000 and 1,300 peaks was higher in the compost than in the soil curve. The finding suggests that this ratio is a parameter that could enable us, even if in a semiquantitative manner, to follow the humification process of the compost when its addition to the soil is not less than the autochthonous organic matter content.Research work supported by CNR, Italy, Special grant I.P.R.A.-Sub-project 1. Paper N. 1531.     

基于景观地形的小流域单元减灾调控评价研究

近年来,中国诸多大中城市内涝灾害频发。武汉市作为城市内涝频发的典型城市,其建成区地表高度（20.0~24.0 m）大多低于外江常年所处的洪水位高度（23.9 m）,在区域性暴雨条件下,极易引发内涝灾害。武汉由于其内涝典型性,2013年被列为全国31个重点防洪城市之一,2015年被列入首批海绵城市试点城市之一。从城市内涝发生机理出发,以水文角度的小流域单元作为内涝风险区划的基本单元,利用小流域单元分析武汉市景观地形要素（地表高程、地表起伏度、地表粗糙度）与城市内涝积水密度的相关性及其影响程度,量算统计出小流域单元的内涝风险等级。基于此,提出武汉市小流域单元减灾地形调控评价。以武汉市作为城市内涝问题的研究案例,以期为武汉市内涝缓解提供新的思考路径,具有典型性和必要性。     

Comparing urban food system characteristics and actions in US and Indian cities from a multi‐environmental impact perspective: Toward a streamlined approach

Food action plans in many global cities articulate interest in multiple objectives including reducing in‐ and trans‐boundary environmental impacts (water, land, greenhouse gas (GHG)). However, there exist few standardized analytical tools to compare food system characteristics and actions across cities and countries to assess trade‐offs between multiple objectives (i.e., health, equity) with environmental outcomes. This paper demonstrates a streamlined model applied for analysis of four cities with varying characteristics across the United States and India, to quantify system‐wide water, energy/GHG, and land impacts associated with multiple food system actions to address health, equity, and environment. Baseline diet analysis finds key differences between countries in terms of meat consumption (Delhi 4; Pondicherry 16; United States 59, kg/capita/year), and environmental impact of processing of the average diet (21%, 19%, <1%, <1% of community‐wide GHG‐emissions for New York, Minneapolis, Delhi, and Pondicherry). Analysis of supply chains finds city average distance (food‐miles) varies (Delhi 420; Pondicherry 200; United States average 1,640 km/t‐food) and the sensitivity of GHG emissions of food demand to spatial variability of energy intensity of irrigation is greater in Indian than US cities. Analysis also finds greater pre‐consumer waste in India versus larger post‐consumer accumulations in the United States. Despite these differences in food system characteristics, food waste management and diet change consistently emerge as key strategies. Among diet scenarios, all vegetarian diets are not found equal in terms of environmental benefit, with the US Government's recommended vegetarian diet resulting in less benefit than other more focused targeted diet changes.     

New entry to the enantioselective formation of substituted cyclohexenes bearing an all-carbon quaternary stereogenic center

Enantioselective formation of cyclohexene derivatives bearing an all-carbon quaternary stereogenic center is described. The racemic cyclohexenes are readily transformed to chiral substituted cyclohexenes in good yield with excellent enantioselectivity and diastereoselectivity by a palladium-mediated deracemization. The resulting products are promising synthetic intermediates of biologically active natural products. This protocol provides us with a new entry to the concise and scalable synthesis of multifunctionalized compounds.