Δψ and ΔpH are equivalent driving forces for proton transport through isolated F0 complexes of ATP synthases

The membrane-embedded F₀ part of ATP synthases is responsible for ion translocation during ATP synthesis and hydrolysis. Here, we describe an in vitro system for measuring proton fluxes through F₀ complexes by fluorescence changes of the entrapped fluorophore pyranine. Starting from purified enzyme, the F₀ part was incorporated unidirectionally into phospholipid vesicles. This allowed analysis of proton transport in either synthesis or hydrolysis direction with Δψ or ΔpH as driving forces. The system displayed a high signal-to-noise ratio and can be accurately quantified. In contrast to ATP synthesis in the Escherichia coli F₁F₀ holoenzyme, no significant difference was observed in the efficiency of ΔpH or Δψ as driving forces for H⁺-transport through F₀. Transport rates showed linear dependency on the driving force. Proton transport in hydrolysis direction was about 2400 H⁺/(s × F₀) at Δψ of 120 mV, which is approximately twice as fast as in synthesis direction. The chloroplast enzyme was faster and catalyzed H⁺-transport at initial rates of 6300 H⁺/(s × F₀) under similar conditions. The new method is an ideal tool for detailed kinetic investigations of the ion transport mechanism of ATP synthases from various organisms.     

Kinetic models of coupling between H+ and Na+-translocation and ATP synthesis/hydrolysis by F0F1-ATPases: Can a cell utilize both\Delta \bar \mu _{H^ + } and\Delta \bar \mu _{Na^ + } for ATP synthesis underin vivo conditions using the same enzyme?

Kinetic models of the F₀F₁-ATPase able to transport H⁺ or/and Na⁺ ions are proposed. It is assumed that (i) H⁺ and Na⁺ compete for the same binding sites, (ii) ion translocation through F₀ is coupled to the rate-limiting step of the F₁-catalyzed reaction. The main characteristics of the dependences of ATP synthesis and hydrolysis rates on Δφ, ΔpH, and ΔpNa are predicted for various versions of the coupling model. The mechanism of the switchover from \(\Delta \bar \mu _{H^ + } \) -dependent synthesis to the \(\Delta \bar \mu _{Na^ + } \) -dependent one is demonstrated. It is shown that even with a drastic drop in \(\Delta \bar \mu _{H^ + } \) , ATP hydrolysis by the proton mode of catalysis can be effectively inhibited by Δφ and ΔpNa. The results obtained strongly support the possibility that the same F₀F₁-ATPase in bacterial cells can utilize both \(\Delta \bar \mu _{H^ + } \) and \(\Delta \bar \mu _{Na^ + } \) for ATP synthesis underin vivo conditions.     

pH-dependent Ca2+ binding to the F0 c-subunit affects proton translocation of the ATP synthase from Synechocystis 6803

It was shown before (Wooten, D. C., and Dilley, R. A. (1993) J. Bioenerg. Biomembr. 25, 557–567; Zakharov, S. D., Li, X., Red'ko, T. P., and Dilley, R. A. (1996) J. Bioenerg. Biomembr. 28, 483–493) that pH dependent reversible Ca²⁺ binding near the N- and C-terminal end of the 8 kDa subunit c modulates ATP synthesis driven by an applied pH jump in chloroplast and E. coli ATP synthase due to closing a proton gate proposed to exist in the F₀ H⁺ channel of the F₀F₁ ATP synthase. This mechanism has further been investigated with the use of membrane vesicles from mutants of the cyanobacterium Synechocystis 6803. Vesicles from a mutant with serine at position 37 in the hydrophilic loop of the c-subunit replaced by the charged glutamic acid (strain plc 37) has a higher H⁺/ATP ratio than the wild type and therefore shows ATP synthesis at low values of _H ⁺. The presence of 1 mM CaCl₂ during the preparation and storage of these vesicles blocked acid–base jump ATP formation when the pH of the acid side (inside) was between pH 5.6 and 7.1, even though the pH of the acid–base jump was thermodynamically in excess of the necessary energy to drive ATP formation at an external pH above 8.28. That is, in the absence of added CaCl₂, ATP formation did occur under those conditions. However, when the base stage pH was 7.16 and the acid stage below pH 5.2, ATP was formed when Ca²⁺ was present. This is consistent with Ca²⁺ being displaced by H⁺ ions from the F₀ on the inside of the thylakoid membrane at pH values below about 5.5. Vesicles from a mutant with the serine of position 3 replaced by a cysteine apparently already contain some bound Ca²⁺ to F₀. Addition of 1 mM EGTA during preparation and storage of those vesicles shifted the otherwise already low internal pH needed for onset of ATP synthesis to higher values when the external pH was above 8. With both strains it was shown that the Ca²⁺ binding effect on acid–base induced ATP synthesis occurs above an internal pH of about 5.5. These results were corroborated by ⁴⁵Ca²⁺- ligand blot assays on organic solvent soluble preparations containing the 8 kDa F₀ subunit c from the S-3-C mutant ATP synthase, which showed ⁴⁵Ca²⁺ binding as occurs with the pea chloroplast subunit III. The phosphorylation efficiency (P/2e), at strong light intensity, of Ca²⁺ and EGTA treated vesicles from both strains were almost equal showing that Ca²⁺ or EGTA have no other effect on the ATP synthase such as a change in the proton to ATP ratio. The results indicate that the Ca²⁺ binding to the F₀ H⁺ channel can block H⁺ flux through the channel at pH values above about 5.5, but below that pH protons apparently displace the bound Ca²⁺, opening the CF₀ H⁺ channel between the thylakoid lumen and H⁺ conductive channel.     

Transport of protons and potassium ions across the membranes of bacteria <Emphasis Type="Italic">Enterococcus hirae</Emphasis> dependent on ATP and nicotinamide adenine dinucleotides

The transport of protons and potassium ions across the membranes of the bacteria Enterococcus hirae growing in an alkaline medium (pH 8.0) or under experimental conditions (pH 7.5) during glucose fermentation accomplished by a KtrI system of absorption of potassium ions, which can interact with F₀F₁-ATPase to form at H⁺-K⁺-pump, has been studied. It was found on cells with a high membrane permeability that the administration of nicotinamide adenine dinucleotides results in the potassium absorption which is insensitive to the inhibitor of F₀F₁-ATPase N,N′-dicyclohexylcarbodiimide. It is assumed that, along with the KtrI system which interacts with F₀F₁-ATPase, a separate KtrI or another K⁺ absorption system operates in these bacteria under particular conditions, which is dependent on NAD⁺ +NADH. Presumably, these interact with this system, changing its conformational state required for the transition to the “active” form.     

pH homeostasis and ATP synthesis: studies of two processes that necessitate inward proton translocation in extremely alkaliphilic Bacillus species

Alkaliphilic Bacillus species that are isolated from nonmarine, moderate salt, and moderate temperature environments offer the opportunity to explore strategies that have developed for solving the energetic challenges of aerobic growth at pH values between 10 and 11. Such bacteria share many structural, metabolic, genomic, and regulatory features with nonextremophilic species such as Bacillus subtilis. Comparative studies can therefore illuminate the specific features of gene organization and special features of gene products that are homologs of those found in non-extremophiles, and potentially identify novel gene products of importance in alkaliphily. We have focused our studies on the facultative alkaliphile Bacillus firmus OF4, which is routinely grown on malate-containing medium at either pH 7.5 or 10.5. Current work is directed toward clarification of the characteristics and energetics of membrane-associated proteins that must catalyze inward proton movements. One group of such proteins are the Na⁺/H⁺ antiporters that enable cells to adapt to a sudden upward shift in pH and to maintain a cytoplasmic pH that is 2–2.3 units below the external pH in the most alkaline range of pH for growth. Another is the proton-translocating ATP synthase that catalyzes robust production of ATP under conditions in which the external proton concentration and the bulk chemiosmotic driving force are low. Three gene loci that are candidates for Na⁺/H⁺ antiporter encoding genes with roles in Na⁺- dependent pH homeostasis have been identified. All of them have homologs in B. subtilis, in which pH homeostasis can be carried out with either K⁺ or Na⁺. The physiological importance of one of the B. firmus OF4 loci, nhaC, has been studied by targeted gene disruption, and the same approach is being extended to the others. The atp genes that encode the alkaliphile's F₁F_O-ATP synthase are found to have interesting motifs in areas of putative importance for proton translocation. As an initial step in studies that will probe the importance and possible roles of these motifs, the entire atp operon from B. firmus OF4 has been cloned and functionally expressed in an Escherichia coli mutant that has a full deletion of its atp genes. The transformant does not exhibit growth on succinate, but shows reproducible, modest increases in the aerobic growth yields on glucose as well as membrane ATPase activity that exhibits characteristics of the alkaliphile enzyme. Received: January 22, 1998 / Accepted: February 16, 1998     

Prostaglandin F2alpha and insulin stimulate phosphate uptake and (Na+, K+) ATPase activity in resting mouse fibroblast cultures.

The (Na⁺, K⁺)ATPase transport system in resting 3T3 Swiss mouse fibroblasts is rapidly activated by prostaglandin F₂α and insulin, which initiate DNA synthesis in these cells. Prostaglandin F₂α, but not insulin, promotes a rapid increase in P_i uptake which is partially coupled to the Na⁺ pump. This rapid activation of both transport systems occurs by a mechanism which does not require fluctuation of cyclic AMP levels or new protein synthesis. A subsequent protein synthesis-dependent increase in P_i uptake is stimulated by insulin and prostaglandin F₂α. These results suggest that different types of control of membrane transport occur during growth stimulation.     

A Ca/H Antiport System Driven by the Proton Electrochemical Gradient of a Tonoplast H-ATPase from Oat Roots

Two types of ATP-dependent calcium (Ca²⁺) transport systems were detected in sealed microsomal vesicles from oat roots. Approximately 80% of the total Ca²⁺ uptake was associated with vesicles of 1.11 grams per cubic centimeter and was insensitive to vanadate or azide, but inhibited by NO₃⁻. The remaining 20% was vanadate-sensitive and mostly associated with the endoplasmic reticulum, as the transport activity comigrated with an endoplasmic reticulum marker (antimycin A-insensitive NADH cytochrome c reductase), which was shifted from 1.11 to 1.20 grams per cubic centimeter by Mg²⁺.

Like the tonoplast H⁺-ATPase activity, vanadate-insensitive Ca²⁺ accumulation was stimulated by 20 millimolar Cl⁻ and inhibited by 10 micromolar 4,4′-diisothiocyano-2,2′-stilbene disulfonic acid or 50 micromolar N,N′-dicyclohexylcarbodiimide. This Ca²⁺ transport system had an apparent K_m for Mg-ATP of 0.24 millimolar similar to the tonoplast ATPase. The vanadate-insensitive Ca²⁺ transport was abolished by compounds that eliminated a pH gradient and Ca²⁺ dissipated a pH gradient (acid inside) generated by the tonoplast-type H⁺-ATPase. These results provide compelling evidence that a pH gradient generated by the H⁺-ATPase drives Ca²⁺ accumulation into right-side-out tonoplast vesicles via a Ca²⁺/H⁺ antiport. This transport system was saturable with respect to Ca²⁺ (K_m apparent = 14 micromolar). The Ca²⁺/H⁺ antiport operated independently of the H⁺-ATPase since an artifically imposed pH gradient (acid inside) could also drive Ca²⁺ accumulation. Ca²⁺ transport by this system may be one major way in which vacuoles function in Ca²⁺ homeostasis in the cytoplasm of plant cells.

     

The functions of plant cation/proton antiporters

The cation/H⁺ exchange is a basic process in transmembrane transport. The acquisition of genome sequences has now established that plants possess genes encoding a large number of cation/proton antiporter 1 (CPA1) proteins, few of which have been characterized with respect to their contribution to ion homeostasis. The CPA1s comprise plasma membrane, vacuolar, and endosomal forms, and they have been identified as important for a salinity tolerance. They are, however, also involved in both the control of cellular pH and K⁺ homeostasis, and regulate processes over a wide range of physiological events, from vesicle trafficking to development.     

On the mechanism of the reconstitution of F1-depleted ATPase complex with purified F1: Possible conformational effects

The membrane sector (F₀) of H⁺-ATPase was prepared by trypsin and urea treatment of F₁-F₀ and reconstituted with purified F₁. The oligomycin sensitivity of the reconstituted F₁-F₀ complex obtained by treating F₁ or F₀ with Mg²⁺ before binding is much higher than that obtained without Mg²⁺ treatment. The greater change in the intrinsic fluorescence of the reconstituted F₁-F₀ complex obtained by Mg²⁺ treatment suggests that conformational changes may occur during the reconstitution. We deduce that Mg²⁺ binds to membrane lipids, thus decreasing membrane fluidity and changing the physical state of the lipids to provide a suitable microenvironment for conformational changes in F₀. The data also suggest that the conformational change in the F₀ portion of the F₁-F₀ complex can be transmitted to the F₁ portion, the conformation of which is in turn altered, resulting in the formation of an F₁-F₀ complex with high oligomycin sensitivity. On the other hand, Mg²⁺ may act on F₁ directly to induce a suitable conformational change which is then trnsmitted to F₀, resulting in the formation of an H⁺-ATPase with greater sensitivity to oligomycin.Abbreviations STED 0.25 M sucrose, 10 mM Tris-SO₄, 0.2 mM EDTA, and 1 mM dithiothreitol, pH 8.0 - NADH nicotinamide adenine dinucleotide, reduced form - olig. oligomycin - OSCP oligomycin sensitivity conferring protein - F₆ coupling factor 6 - F₁ coupling factor one (or F₁-ATPase) - F₁ ^{+Mg 2+} and F₁ ^{–Mg 2+} the F₁ treated and untreated with 1 mM Mg²⁺ respectively - F₀ the membrane sector proteins of the H⁺-ATPase - TUF₀ trypsin-urea – F₀ - EUF₀ EDTA-urea – F₀ - F₀ ^{+Mg 2+} and F₀ ^{–Mg 2+} the F₀ treated and untreated with 1 mM Mg²⁺ respectively - (F₁ · F₀)^{+Mg 2+} and (F₁ · F₀)^{–Mg 2+} the reconstituted F₁ · F₀ complex containing Mg²⁺-treated F₁ and F₀ and untreated F₁ and F₀ respectively - F₁ · F₀ ^{+Mg 2+} and F₁ · F₀ ^{–Mg 2+} the reconstituted H⁺-ATPase complex derived from the binding of purified F₁ to the F₀ treated and untreated with Mg²⁺ respectively - F₁ ^{+Mg 2+} · F₀ and F₁ ^{–Mg 2+} · F₀ the reconstituted H⁺-ATPase derived from the binding of F₀ to the purified F₁ treated and untreated with Mg²⁺ respectively     

Flexible coupling between light-dependent electron and vectorial proton transport in illuminated leaves of C3 plants. Role of photosystem I-dependent proton pumping

The role of cyclic electron transport has been re-examined in leaves of C₃ plants because the bioenergetics of chloroplasts (H⁺/e = 3 in the presence of a Q-cycle; H⁺/ATP = 4 of ATP synthesis) had suggested that cyclic electron flow has no function in C₃ photosynthesis. After light activation of pea leaves, the dark reduction of P700 (the donor pigment of PSI) following far-red oxidation was much accelerated. This corresponded to loss of sensitivity of P700 to oxidation by far-red light and a large increase in the number of electrons available to reduce P700⁺ in the dark. At low CO₂ and O₂ molar ratios, far-red light was capable of decreasing the activity of photosystem II (measured as the ratio of variable to maximal chlorophyll fluorescence, F_v/F_m) and of increasing light scattering at 535 nm and zeaxanthin synthesis, indicating formation of a transthylakoid pH gradient. Both the light-induced increase in the number of electrons capable of reducing far-red-oxidised P700 and the decline in F_v/F_m brought about by far-red in leaves were prevented by methyl viologen. Antimycin A inhibited CO₂-dependent O₂ evolution of pea leaves at saturating but not under limiting light; in its presence, far-red light failed to decrease F_v/F_m. The results indicate that cyclic electron flow regulates the quantum yield of photosystem II by decreasing the intrathylakoid pH when there is a reduction in the availability of electron acceptors at the PSI level (e.g. during drought or cold stresses). It also provides ATP for the carbon-reduction cycle under high light. Under these conditions, the Q-cycle is not able to maintain a H⁺/e ratio of 3 for ATP synthesis: we suggest that the ratio is flexible, not obligatory. Received: 23 February 1999 / Accepted: 19 August 1999     

H2O2 and cytosolic Ca2+ signals triggered by the PM H+‐coupled transport system mediate K+/Na+ homeostasis in NaCl‐stressed Populus euphratica cells

Using confocal microscopy, X‐ray microanalysis and the scanning ion‐selective electrode technique, we investigated the signalling of H₂O₂, cytosolic Ca²⁺ ([Ca²⁺]_cyt) and the PM H⁺‐coupled transport system in K⁺/Na⁺ homeostasis control in NaCl‐stressed calluses of Populus euphratica. An obvious Na⁺/H⁺ antiport was seen in salinized cells; however, NaCl stress caused a net K⁺ efflux, because of the salt‐induced membrane depolarization. H₂O₂ levels, regulated upwards by salinity, contributed to ionic homeostasis, because H₂O₂ restrictions by DPI or DMTU caused enhanced K⁺ efflux and decreased Na⁺/H⁺ antiport activity. NaCl induced a net Ca²⁺ influx and a subsequent rise of [Ca²⁺]_cyt, which is involved in H₂O₂‐mediated K⁺/Na⁺ homeostasis in salinized P. euphratica cells. When callus cells were pretreated with inhibitors of the Na⁺/H⁺ antiport system, the NaCl‐induced elevation of H₂O₂ and [Ca²⁺]_cyt was correspondingly restricted, leading to a greater K⁺ efflux and a more pronounced reduction in Na⁺/H⁺ antiport activity. Results suggest that the PM H⁺‐coupled transport system mediates H⁺ translocation and triggers the stress signalling of H₂O₂ and Ca²⁺, which results in a K⁺/Na⁺ homeostasis via mediations of K⁺ channels and the Na⁺/H⁺ antiport system in the PM of NaCl‐stressed cells. Accordingly, a salt stress signalling pathway of P. euphratica cells is proposed.     

离子转运蛋白调控钝齿棒杆菌离子和pH稳态促进L-精氨酸合成

L-精氨酸是一种半必需氨基酸,广泛应用于食品、制药、饲料等行业。【目的】当前对L-精氨酸生产菌株的研究,极少涉及离子转运领域。在本研究中,发现在发酵时适量添加外源K~+有利于促进钝齿棒杆菌(Corynebacterium crenatum) SYPA5-5合成L-精氨酸。【方法】在C. crenatum SYPA5-5发酵培养基外源添加0.5 g/L和2.5 g/L的K_3PO_4,取对数期发酵样品进行转录组数据分析,挖掘出K~+转运相关的阳离子转运ATP酶CTAP1以及单价阳离子/H~+逆转运蛋白Mrp1A,研究其在C. crenatum SYPA5-5快速合成L-精氨酸阶段,对菌株生长及L-精氨酸合成的影响。【结果】对基因ctap1和mrp1分别进行敲除和过表达,深入研究突变株对L-精氨酸合成的影响。研究发现同时过表达离子转运蛋白CTAP1和Mrp1A更有利于胞内离子、pH稳态和渗透压调节,最终提高L-精氨酸的产量。在补料分批发酵中分别过表达Mrp1A、CTAP1以及同时过表达Mrp1A和CTAP1的菌株L-精氨酸产量分别达到61.4 g/L、63.9 g/L和65.3 g/L,产率分别为0.383 g/g、0.392 g/g和0.395 g/g,比C. crenatum SYPA5-5分别提高了34.9%、38.0%和39.1%。【结论】CTAP1是特异性的K~+转运ATP酶,可以将培养基中的K~+运输到胞内。同时Mrp1A可将胞内K~+和Na~+等单价阳离子运输到胞外,将胞外H~+运输至胞内,中和胞内L-精氨酸所导致的碱性环境,从而维持胞内pH稳定。CTAP1和Mrp1A的研究为解析离子转运机制和L-精氨酸合成之间的联系奠定了基础。     

Chromosome locations of five genes encoding photosynthetic electron transfer proteins in Arabidopsis thaliana

The chromosome locations of nuclear genes encoding four photosynthetic electron transfer proteins have been determined by examining restriction fragment length polymorphisms in F₈recombinant inbred lines of Arabidopsis thaliana. The single-copy PetC gene encoding the chloroplast Rieske FeS protein was mapped to the top of chromosome 4, whereas the PetE and PetF genes encoding plastocyanin and ferredoxin, respectively, were mapped to different parts of chromosome 1. Two PetH genes encoding ferredoxin-NADP⁺oxidoreductase were mapped to the top of chromosome 1 and the bottom of chromosome 5.     

Transport of H+, K+, Na+ and Ca++ in Streptococcus

Summary The streptococci differ from other bacteria in that cation translocations (with the possible exception of one of the K⁺ uptake systems) occur by primary transport systems, i.e., by cation pumps which use directly the free energy released during hydrolysis of chemical bonds to power transport. Transport systems in other bacteria, especially for Na⁺ and Ca⁺⁺, are often secondary, using the free energy of another ion gradient to drive cation transport. In streptococci H⁺ efflux occurs via the F₁F₀-ATPase. This enzyme is composed of eight distinct subunits. Three of the subunits are embedded in the membrane and form a H⁺ channel; this is called the F₀ portion of the enzyme. The other five subunits form the catalytic part of the enzyme, called F₁, which faces the cytoplasm and can easily be stripped from the membrane. Physiologically, this enzyme functions as a H⁺-ATPase, pumping protons out of the cell to form an electrochemical proton gradient, . The F₁F₀-ATPase, however, is fully reversible and if supplied with P_i, ADP and a + of sufficient magnitude (ca –200 mv) catalyzes the synthesis of ATP. Streptococcus faecalis can accumulate K⁺ and establish a gradient of 50 000:1 (in>out) under some conditions. Uptake occurs by two transport systems. The dominant, constitutive system requires both an electrochemical proton gradient and ATP to operate. The minor, inducible K⁺ transport system, which has many similarities to the K⁺-ATPase of the Kdp transport system found in Escherichia coli, requires only ATP to power K⁺ uptake.Sodium extrusion occurs by a Na⁺/H⁺-ATPase. Exchange is electroneutral and there is no requirement for a . The possibility that the Na⁺/H⁺-ATPase may consist of two parts, a catalytic subunit and a Na⁺/H⁺ antiport subunit, is suggested by the finding that damage to the Na⁺ transport system either through mutation or protease action leads to the appearance of -requiring Na⁺/H⁺ antiporter activity.Ca⁺⁺ like Na⁺ is extruded from metabolizing, intact cells. Transport requires no but does require ATP. Reconstitution of Ca⁺⁺ transport activity with accompanying Ca⁺⁺-stimulated ATPase activity into proteoliposomes suggests that Ca⁺⁺ is transported by a Ca⁺⁺-translocating ATPase.Where respiring organelles and bacteria use secondary transport systems the streptococci have developed cation pumps. The streptococci, which are predominantly glycolyzing bacteria, generate a much inferior to that of respiring organisms and organelles. The cation pumps may have developed simply in response to an inadequate .Abbreviations electrochemical potential of protons - membrane potential - pH pH gradient - p proton-motive force - DCCD N,Na¹-dicyclohexlcarbodiimide - TCS tetrachlorosalicylanilide - FCCP carbonylcyanide-p-trifluoromethylphenylhydrazone - CCCP carbonylcyanie-m-chlorophenylhydrazone - TPMP⁺ triphenylmethyl phosphonium ion - DDA⁺ dibenzyldimethylammonium ion - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - EGTA ethyleneglycol-bis (amino-ethyl-ether)-N,N-tetraacetic acid     

The Increase in the Number of Accessible SH-Groups in the Enterococcal Membrane Vesicles by ATP and Nicotinamide Adenine Dinucleotides

The number of accessible SH groups was determined in membrane vesicles prepared from Enterococcus hirae grown under anaerobic conditions at alkaline pH (pH 8.0). Addition of ATP or nicotinamide adenine dinucleotides (NAD⁺+NADH) to the vesicles caused a ∼4-fold or ∼1.9-fold increase in the number of SH-groups, respectively. This was inhibited by treatment with N-ethylmaleimide. The increase was significant when ATP and NAD⁺+NADH both were added. The change was lacking in the presence of the F₀F₁-ATPase inhibitors N,N′-diclohexylcarbodiimide or sodium azide. This was also absent in atp mutant with defect in the F₀F₁-ATPase and, in addition, it was less in potassium ion–free medium. These results are correlated with data about K⁺-dependent F₀F₁-ATPase activity, suggesting a relationship between the F₀F₁-ATPase and K⁺ uptake Trk-like system. The latter may be regulated by NAD or NADH mediating conformational changes.     

海底热液环境中嗜中性微需氧铁氧化菌的多样性、生物矿化作用及其代谢特征

铁元素是深海热液活动产物的主要成分之一,也是热液喷口处化能自养微生物生态系统的重要驱动元素。以Zetaproteobacteria为典型代表的嗜中性微需氧铁氧化菌是海底喷口及其周围环境中生物介导的Fe²⁺氧化这一生物矿化作用的主要驱动者。这些铁氧化菌通过氧化Fe²⁺获取维持自身代谢所必需的能量,同时分泌有机质将氧化后的不溶铁（氧化物或氢氧化物）沉淀于细胞外,形成具有螺旋丝带状、中空长杆状、分叉管状以及其他具有特殊形貌特征的显微结构体,进而堆积成广泛分布于海底的富铁氧化物/氢氧化物。越来越多的研究表明,编码细胞色素孔蛋白的cyc2基因是Zetaproteobacteria铁氧化菌进行Fe²⁺氧化的关键基因,而细胞色素c或其他周质细胞色素则是Fe²⁺氧化过程中的关键电子传递载体。基于宏基因组分析的系列研究揭示了Zetaproteobacteria普遍具有多种与氮、硫、氢以及砷元素循环密切相关的功能基因与代谢途径,暗示了其在上述元素循环过程中的潜在作用。本文系统地总结了海底热液喷口及其周围环境中发现的嗜中...     

Functional Gene Differences in Soil Microbial Communities from Conventional,Low-Input,and Organic Farmlands

Various agriculture management practices may have distinct influences on soil microbial communities and their ecological functions. In this study, we utilized GeoChip, a high-throughput microarray-based technique containing approximately 28,000 probes for genes involved in nitrogen (N)/carbon (C)/sulfur (S)/phosphorus (P) cycles and other processes, to evaluate the potential functions of soil microbial communities under conventional (CT), low-input (LI), and organic (ORG) management systems at an agricultural research site in Michigan. Compared to CT, a high diversity of functional genes was observed in LI. The functional gene diversity in ORG did not differ significantly from that of either CT or LI. Abundances of genes encoding enzymes involved in C/N/P/S cycles were generally lower in CT than in LI or ORG, with the exceptions of genes in pathways for lignin degradation, methane generation/oxidation, and assimilatory N reduction, which all remained unchanged. Canonical correlation analysis showed that selected soil (bulk density, pH, cation exchange capacity, total C, C/N ratio, NO₃⁻, NH₄⁺, available phosphorus content, and available potassium content) and crop (seed and whole biomass) variables could explain 69.5% of the variation of soil microbial community composition. Also, significant correlations were observed between NO₃⁻ concentration and denitrification genes, NH₄⁺ concentration and ammonification genes, and N₂O flux and denitrification genes, indicating a close linkage between soil N availability or process and associated functional genes.     

Relation of potassium uptake to proton transport and activity of hydrogenases in Escherichia coli grown at low pH

Escherichia coli grown under anaerobic conditions in acidic medium (pH 5.5) upon hyperosmotic stress accumulates potassium ions mainly through the Kup system, the functioning of which is associated with proton efflux decrease. It was shown that H⁺ secretion but not glucose-induced K⁺ uptake was inhibited by N,N′-dicyclohexylcarbodiimide (DCC). The inhibitory effect of DCC on the H⁺ efflux was stronger in the trkA mutant with defective potassium transport. The K⁺ and H⁺ fluxes depended on the extent of hyperosmotic stress in the absence or presence of DCC. The decrease in external oxidation/reduction potential and H₂ liberation insensitive to DCC were recorded. It was found that the atpD mutant with nonfunctional F₀F₁-ATPase produced a substantial amount of H₂, while in the hyc mutant (but not the hyf mutant defective in hydrogenases 3 (Hyd-3) and 4 (Hyd-4)) the H₂ production was significantly suppressed. At the same time, the rate of K⁺ uptake was markedly lower in hyfR and hyfB-R but not in hycE or hyfA-B mutants; H⁺ transport was lowered and sensitive to DCC in hyf but not in hyc mutants. The results point to the relationship of K⁺ uptake with the Hyd-4 activity. Novel options of the expression of some hyf genes in E. coli grown at pH 5.5 are proposed. It is possible that the hyfB-R genes expressed under acidic conditions or their gene products interact with the gene coding for the Kup protein or directly with the Kup system.     

Downregulation of the Creatine Transporter SLC6A8 by JAK2

Janus-activated kinase-2 (JAK2) participates in the regulation of the Na⁺-coupled glucose transporter SGLT1 and the Na⁺-coupled amino acid transporter SLC6A19. Concentrative cellular creatine uptake is similarly accomplished by Na⁺-coupled transport. The carrier involved is SLC6A8 (CreaT). The present study thus explored whether JAK2 regulates the activity of SLC6A8. To this end, cRNA encoding SLC6A8 was injected into Xenopus oocytes with or without cRNA encoding wild-type JAK2, constitutively active ^V617FJAK2 or inactive ^K882EJAK2. Electrogenic creatine transport was determined in those oocytes by dual-electrode voltage-clamp experiments. In oocytes injected with cRNA encoding SLC6A8 but not in oocytes injected with water or with cRNA encoding JAK2 alone, addition of 1 mM creatine to the extracellular bath generated an inward current (I _crea). In SLC6A8 expressing oocytes I _crea was significantly decreased by coexpression of JAK2 or ^V617FJAK2 but not by coexpression of ^K882EJAK2. According to kinetic analysis, coexpression of JAK2 decreased the maximal transport rate without significantly modifying the affinity of the carrier. In oocytes expressing SLC6A8 and ^V617FJAK2 I _crea was gradually increased by the JAK2 inhibitor AG490 (40 μM). In SLC6A8 and JAK2 coexpressing oocytes the decline of I _crea following disruption of carrier insertion with brefeldin A (5 μM) was similar in the absence and presence of JAK2. In conclusion, JAK2 is a novel regulator of the creatine transporter SLC6A8, which downregulates the carrier, presumably by interference with carrier protein insertion into the cell membrane.