Evolution of membrane bioenergetics

One of the first problems encountered by primitive cells was that of volume regulation; the continuous entry of ions, (eg, NaCl) and water in response to the internal colloid osmotic pressure threatening to destroy the cell by lysis. We propose that to meet this environmental challenge cells evolved an ATP-driven proton extrusion system plus a membrane carrier that would exchange external protons with internal Na⁺. With the appearance of the ability to generate proton gradients, additional mechanisms to harness this source of energy emerged. These would include proton-nutrient cotransport, K⁺ accumulation, nucleic acid entry, and motility. A more efficient system for the uptake of certain carbohydrates by vectorial phosphorylation via the PEP-phosphotransferase system probably appeared rather early in the evolution of anaerobic bacteria. The reversal of the proton-ATPase reaction to give net ATP synthesis became possible with the development of other types of efficient proton transporting machinery. Either light-driven bacterial rhodopsin or a redox system coupled to proton translocation would have served this function. Oxidation of one substrate coupled to the reduction of another substrate by membrane-bound enzymes evolved in such a manner that protons were extruded from the cell during the reaction. The progressive elaboration of this type of redox proton pump permitted the use of exogenous electron acceptors, such as fumarate, sulfate, and nitrate. The stepwise growth of these electron transport chains required the accretion of several flavoproteins, iron-sulfur proteins, quinones, and cytochromes. With modifications of these four basic components a chlorophyll-dependent photosynthetic system was subsequently evolved. The oxygen that was generated by this photosynthetic system from water would eventually accumulate in the atmosphere of the earth. With molecular oxygen present, the emergence of cytochrome oxidase would complete the respiratory chain. The proton economy of membrane energetics has been retained by most present-day microorganisms, mitochondria, chloroplasts, and cells of higher plants. A secondary use of the energy stored as an electrochemical difference of Na⁺ for powering membrane events probably also evolved in microorganisms. The exclusive use of the Na⁺ economy is distinctive of the plasma membrane of animal cells; the Na⁺-K⁺ ATPase sets up an electrochemical Na⁺ gradient that provides the energy for osmoregulation, Na⁺-nutrient cotransport, and the action potential of excitable cells.     

Effect of carbon monoxide on metabolism and ultrastructure of carboxydobacteria

Growth of Seliberia carboxydohydrogena was inhibited by CO at 10 to 40% (v/v), resulting in increased substrate utilization and enhanced synthesis of cytochromes and cyclopropane and saturated fatty acids. The bacteria showed increased formation of new membrane structures, with pronounced folding of their cell walls.     

Large scale preparations of photosynthetic catalysts from cyanobacteria

Large scale preparations of photosynthetic catalysts from cyanobacteria afford special advantages in the discovery and the study of these proteins. Here, we present information on obtaining cyanobacteria from laboratory cultivation, commercial sources and from natural blooms. Procedures for the breakage and fractionation of large amounts of cells are reviewed. Since much of this information is not of a conventional sort, it may provide special help when the need for a large amount of a specific protein arises.     

Extracellular Fe(III) reductase structure reveals a modular organization enabling S-layer insertion and electron transfer to insoluble substrates

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Multiple roles of released c-type cytochromes in tuning electron transport and physiological status of Geobacter sulfurreducens

Dissimilatory metal-reducing bacteria (DMRB) can transfer electrons to extracellular insoluble electron acceptors and play important roles in geochemical cycling, biocorrosion, environmental remediation, and bioenergy generation. c-type cytochromes (c-Cyts) are synthesized by DMRB and usually transported to the cell surface to form modularized electron transport conduits through protein assembly, while some of them are released as extracellularly free-moving electron carriers in growth to promote electron transport. However, the type of these released c-Cyts, the timing of their release, and the functions they perform have not been unrevealed yet. In this work, after characterizing the types of c-Cyts released by Geobacter sulfurreducens under a variety of cultivation conditions, we found that these c-Cyts accumulated up to micromolar concentrations in the surrounding medium and conserved their chemical activities. Further studies demonstrated that the presence of c-Cyts accelerated the process of microbial extracellular electron transfer and mediated long-distance electron transfer. In particular, the presence of c-Cyts promoted the microbial respiration and affected the physiological state of the microbial community. In addition, c-Cyts were observed to be adsorbed on the surface of insoluble electron acceptors and modify electron acceptors. These results reveal the overlooked multiple roles of the released c-Cyts in acting as public goods, delivering electrons, modifying electron acceptors, and even regulating bacterial community structure in natural and artificial environments.     

Chromatographic and catalytic properties of multiple forms of rabbit pulmonary cytochromes P-450

Rabbit pulmonary cytochrome P-450 forms 2,5, and 6 were resolved using anion-exchange high-performance liquid chromatography (HPLC) and their properties compared with rabbit liver cytochrome P-450 isozymes LM₂ and LM₆. Although rabbit pulmonary form 2 and liver LM₂ had similar electrophoretic mobilities and similar substrate specificities in reconstitution experiments, they differed in their HPLC elution profiles. High-performance liquid chromatography of pulmonary microsomes from rabbits treated with 3-methylcholanthrene (3-MC) revealed the induction of form 6 isozyme, which had a retention time, electro-phoretic mobility, and substrate specificity similar to those of rabbit liver LM₆. In reconstitution experiments, forms 2 and 6 showed the highest substrate specificities toward benzphetamine and 7-ethoxyresorufin, respectively. Rabbit lung cytochrome P-450 form 5 was relatively inactive toward all substrates tested.     

Changes in the Constitution of Thylakoid Membranes in Spruce Needles During an Open-top Chamber Experiment

The goal of the presented paper was to study the emission effects of natural air pollutants on the protein complexes of the thylakoid membrane. The tests were carried out in the frame of a long-term experiment in which spruce trees kept in open-top chambers with unfiltered ambient-air were compared to spruce trees in chambers with purified-air. The reaction centres of photosystem I (P-700), cytochrome f, cytochrome b-563, cytochrome b-559, as well as the oxidation speed of the antennae chlorophylls were quantified. The concentrations of the cytochromes f and b-563 indicate a marked annual rhythm with decreased concentrations during the summer months. The spruce trees in chambers with ambient-air showed a smaller amount of the studied redox components in relation to 1000 molecules of chlorophyll than did the spruce trees in chambers exposed to purified-air. In addition, increased oxidation speed of antennae chlorophylls could be observed on the isolated thylakoid membranes of the spruce trees in chambers with ambient-air conditions. A relationship between the oxidation speed and the ozone concentration of the ambient air could be observed, i.e. with increasing ozone levels the oxidation of the antennae chlorophylls accelerated. However, the damage occurred only with a temporary delay (the so-called memory effect). In case of the cytochromes f and b-563 (components of the cytochrome b₆f-complex), a chamber effect related to changed light conditions became obvious when comparing spruce trees kept in chambers to trees left in their natural surrounding. The reduced photosynthetically active radiation — it is reduced in the chambers by 10 ? 30% — led to a decrease of both cytochromes. In spite of the effects due to the chambers, the results indicate that ozone could be an effective damage factor and this will be of importance with regard to the situation in the low mountain range of Germany.