Utilization of mercapto-2-ethanol as medium reductant for determination of the metabolic response of methanogens towards inorganic sulfur compounds

Abstract Mercapto-2-ethanol was examined as a nontoxic and non-metabolizable reducing agent for growth of methanogens. It was used as a medium reductant to prove that Methanobacterium thermoautotrophicum and Methanobacterium strain ivanov grew with either sulfide or elemental sulfur as the sole source of nutrient sulfur but not with sulfate, thiosulfate, sulfite or dithionite. The later inorganic sulfur sources, except sulfate, were potent inhibitors of growth and methanogenesis at 5 mM. The practical utility of mercapto-2-ethanol as a reducing agent and the toxicity of inorganic sulfur sources on metabolic activity of the methanogens are discussed.     

Floristic characterisation of alkali soils in northwestern India

Summary Floristic composition studied in a 40 hectares representative site of alkali soils in the Indo-gangetic plains of Northwestern India revealed a remarkably restricted spectrum of natural vegetation. Soil analysis of specific niches, occupied by aggregations of different species, was employed to identify alkali halophytes. Response functions of eight prominent species to increasing levels of soil alkalinity, studied in pot culture, showed that most of them were adapted to alkali soils. Based on the computed importance value indices and observed biomass production maxima, it has been inferred thatSporobolus marginatus, Sporobulus coromandelianus, Diplachne fusca andChloris barbata, qualify as plant indicators of high-alkali soil conditions.     

Artificial inhibitory effects of sulfite on photosystem II activity measured by oxygen evolution in chloroplasts

In this report we demonstrate sulfite interaction with oxygen and PSII electron acceptors (ferricyanide and para-benzoquinone) during measurement of oxygen evolution in chloroplasts. Redox potentials of oxygen, ferricyanide and para-benzoquinone allow them to compete for sulfite. Without taking this into account, sulfite inhibition of oxygen evolution can be overestimated, since sulfite consumes oxygen and reduces ferricyanide or para-benzoquinone during the measurement. In order to correctly measure the rate of oxygen evolution in chloroplasts, it is necessary to avoid presence of sulfite during the measurement. After overcoming the artifact, mentioned above, we confirm the sulfite inhibition of oxygen evolution in chloroplasts but at a lesser extent than earlier reported. This, however, is a pretreatment effect.Abbreviations Chl Chlorophyll - EDTA Ethylenediamine Tetraacetic Acid - FeCN Potassium Ferricyanide - Hepes N-2-Hydroxyethylpiperazine-N¹-2-ethanesulfonic acid - pBQ Para-benzoquinone - PSII photosystem II     

IMPROVED PROCEDURES FOR THE CLONING AND PURIFICATION OF MICROCYSTIS CULTURES (CYANOPHYTA)1

A cloned axenic culture of Microcystis Kützing was obtained by combining two procedures: a) the disaggregation of multicellular Microcystis colonies by dilution into deionized water, and b) the selective growth of Microcystis in agar media containing Na₂S, which inhibited or killed the associated contaminants. Microcystis growth was stimulated by 0.3–1 mM Na₂SO₃, but not by 0.1–33 mM Na₂SO₄. Although Microcystis cells survived temporary exposure to high Na₂S concentrations, their growth was not stimulated by 1 × 10^?5 to 1.0 M Na₂S. Possible metabolic roles of reduced sulfur compounds are considered. Microcystis colonies disaggregated to unicells at ionic concentrations below 1 mM for univalent cations, 10–100 μM for the divalent cations, and 3–10 μM for Fe³⁺. Higher cation concentrations prompted cell aggregation. With > 100 mM Fe³⁺, the Microcystis capsule appeared rust-colored. Neither nonionic solutes nor anions detectably influenced aggregation. These observations suggest cation interactions with the Microcystis capsule and are discussed with regard to: a) possible siderochrome activity, cation chelation or luxury uptake of cations, b) the questionability of using cell aggregation as a criterion for identifying Microcystis in samples of unknown ionic strength, c) the utility of low ionic strength media in releasing contaminating bacteria from the capsule and in obtaining algal unicells for cloning, and d) a model for cation interactions with the capsule.     

Dissimilatory sulfite reductase from Archaeoglobus profundus and Desulfotomaculum thermocisternum: phylogenetic and structural implications from gene sequences

The genes encoding the α- and β-subunits of dissimilatory sulfite reductase, dsrAB, from the hyper-thermophilic archaeon Archaeoglobus profundus and the thermophilic gram-positive bacterium Desulfotomaculum thermocisternum were cloned and sequenced. The dsrAB genes are contiguous, and most probably comprise an operon also including a dsrD homolog, a conserved gene of unknown function located downstream of dsrAB in all four sulfate reducers so far sequenced. Sequence comparison confirms that dissimilatory sulfite reductase, Dsr, is a highly conserved enzyme. A phylogenetic analysis using the available Dsr sequences, including Dsr-like proteins from nonsulfate reducers, suggests a paralogous origin of the α- and β-subunits. Furthermore, the Dsr from sulfate reducers forms a separate cluster, with Dsr from the bacterial sulfate reducers Desulfotomaculum thermocisternum and Desulfovibrio vulgaris branching together, next to Dsr from Archaeoglobus profundus and Archaeoglobus fulgidus. Based on an alignment with the assimilatory sulfite reductase from Escherichia coli, the amino acid residues involved in binding of sulfite, siroheme, and [Fe₄S₄]-clusters have been tentatively identified, which is consistent with the binding of two sirohemes and four [Fe₄S₄]-clusters per α₂β₂ structure. The evolution of Dsr and the structural basis for the binding of substrate and cofactors are discussed. Received: May 1, 1998 / Accepted: August 10, 1998     

AlS_3PC在荷瘤小白鼠体内动力学分布

采用碱性提取法测量了三磺化铝酞菁（ＡｌＳ３ＰＣ）在正常细胞和肿瘤细胞内的代谢比,得到了ＡｌＳ３ＰＣ在正常细胞和肿瘤细胞内最高潴留浓度的时间,可作为ＰＤＴ治疗肿瘤的最佳时间,另外通过测试得到的数据,建立了一套有关细胞膜的通透性模型,用以解释肿瘤细胞对ＡｌＳ３ＰＣ的亲和性。     

Insensitivity of lepidopteran tissues to ouabain: Absence of ouabain binding and Na+K+ ATPases in larval and adult midgut

Insensitivity of midgut epithelium to ouabain was studied in three phytophyagous Lepidoptera: the tobacco hornworm. Manduca sexta, the Cecropia silkmoth. Hyalophora cecropia, and the Monarch butterfly, Danaus plexippus. The midgut failed to selectively bind ouabain in the presence of 8 mM K^?. The presence of K⁺ stimulated ouabain sensitive Na⁺K⁺-ATPases in midgut could not be confirmed. Neuronal tissues collected from the same species at the same stages in development bound ouabain readily, and possessed K⁺ stimulated ouabain sensitive Na⁺K⁺-ATPases. It is proposed that alkali metal transport across the midgut epithelium of these phytophagous Lepidoptera occurs via energy-linked processes not requiring Na⁺K⁺-ATPases.     

Structure of the dissimilatory sulfite reductase from the hyperthermophilic archaeon Archaeoglobus fulgidus

Conservation of energy based on the reduction of sulfate is of fundamental importance for the biogeochemical sulfur cycle. A key enzyme of this ancient anaerobic process is the dissimilatory sulfite reductase (dSir), which catalyzes the six-electron reduction of sulfite to hydrogen sulfide under participation of a unique magnetically coupled siroheme-[4Fe-4S] center. We determined the crystal structure of the enzyme from the sulfate-reducing archaeon Archaeoglobus fulgidus at 2-Å resolution and compared it with that of the phylogenetically related assimilatory Sir (aSir). dSir is organized as a heterotetrameric (αβ)₂ complex composed of two catalytically independent αβ heterodimers. In contrast, aSir is a monomeric protein built of two fused modules that are structurally related to subunits α and β except for a ferredoxin domain inserted only into the subunits of dSir. The [4Fe-4S] cluster of this ferredoxin domain is considered as the terminal redox site of the electron transfer pathway to the siroheme-[4Fe-4S] center in dSir. While aSir binds one siroheme-[4Fe-4S] center, dSir harbors two of them within each αβ heterodimer. Surprisingly, only one siroheme-[4Fe-4S] center in each αβ heterodimer is catalytically active, whereas access to the second one is blocked by a tryptophan residue. The spatial proximity of the functional and structural siroheme-[4Fe-4S] centers suggests that the catalytic activity at one active site was optimized during evolution at the expense of the enzymatic competence of the other. The sulfite binding mode and presumably the mechanism of sulfite reduction appear to be largely conserved between dSir and aSir. In addition, a scenario for the evolution of Sirs is proposed.     

DFT studies of the electronic structure and geometry of 18-crown-6, hexaaza[18]annulene, and their complexes with cations of the heavier alkali and alkaline earth metals

DFT calculations for M@C₁₂H₁₂N₆ and M@C₁₂H₂₄O₆ (where M = Rb⁺, Cs⁺, Sr²⁺, and Ba²⁺, C₁₂H₁₂N₆ = hexaaza[18]annulene, and C₁₂H₂₄O₆ = 18-crown-6) were performed using the recently developed model core potential parametrization. Results show that the ions bind more strongly to C₁₂H₁₂N₆ than to 18-crown-6 moiety; the difference is more pronounced for cations with smaller radii.     

Extraction properties for alkali metal picrates of macrocyclic trinuclear (p-cymene)ruthenium(II) and (pentamethylcyclopentadienyl)rhodium(III) complexes

The solvent extraction properties of macrocyclic trinuclear organometallic complexes, [(p-cymene)Ru(pyO₂)]₃ and [Cp^∗Rh(pyO₂)]₃, for Li⁺, Na⁺, and K⁺ picrates have been investigated in a dichloromethane-water system at 25 °C. The extraction rates of the alkali metal picrates with these macrocyclic complex ligands are unusually slow; the shaking times required to attain equilibrium are at least 1 h for [(p-cymene)Ru(pyO₂)]₃ and 20-40 h for [Cp^∗Rh(pyO₂)]₃. From analysis of the equilibrium data, the extraction constants (K_ex = [ML⁺A⁻]_o/[M⁺][L]_o[A⁻]; M⁺ = alkali metal ion, L = macrocyclic ligand, A⁻ = picrate ion, o = organic phase) have been determined. The log K_ex value varies in the sequences, Li⁺ (5.72) > Na⁺ (4.50) > K⁺ (2.88) for [(p-cymene)Ru(pyO₂)]₃ and Li⁺ (4.79) > Na⁺ (2.70) ≈ K⁺ (2.69) for [Cp^∗Rh(pyO₂)]₃. The K_ex values of 6,6-dibenzyl-14-crown-4 (DBz14C4), which is one of the best Li⁺-selective crown ethers, have also been determined for comparison. It is revealed that [Cp^∗Rh(pyO₂)]₃ is much superior to DBz14C4 both in the extractability for Li⁺ and the selectivity for Li⁺ over Na⁺.