Roles of the respiratory Na+ pump in bioenergetics of Vibrio alginolyticus

Bioenergetic characteristics of Na+ pump-defective mutants of a marine bacterium Vibrio alginolyticus were compared with those of the wild type and revertant. Generation of membrane potential and motility at pH 8.5 in the mutants were completely inhibited by a proton conductor, carbonylcyanide m-chlorophenylhydrazone, whereas those in the wild type or revertant were resistant to the inhibitor. Motility and amino acid transport were driven by the electrochemical potential of Na+ not only in the wild type or revertant but also in the mutants. In the absence of the proton conductor, motility and amino acid transport of the mutants did not significantly differ from those of the wild type or revertant even at pH 8.5, where the Na+ pump has maximum activity. Therefore, the electrochemical potential of Na+ in the mutants seemed to be maintained at a normal level by a respiration-dependent H+ pump and Na+/H+ antiporter. On the other hand, growth of the mutants became defective as the medium pH increased, especially on minimal medium. These results indicate that the Na+ pump is an important energy-generating mechanism when nutrients are limited at alkaline pH.     

Demethylation of methyl-accepting chemotaxis proteins in Escherichia coli induced by the repellents glycerol and ethylene glycol.

The addition of glycerol or ethylene glycol caused not only severe tumbling but also a drastic decrease in the methylation level of methyl-accepting chemotaxis proteins (MCPs) in Escherichia coli. Experiments with various mutants having defects in their MCPs showed that the demethylation occurred in all three kinds of MCPs, MCPI, II, and III. The addition of an attractant to the glycerol- or ethylene glycol-treated cells resulted in a distinct increase in the methylation level of the relevant MCP, indicating that glycerol and ethylene glycol do not directly damage the methylation-demethylation system in the cell. The time courses of adaptation and MCP demethylation upon addition of these repellents were consistent with each other. Furthermore, both the response time and the extent of MCP demethylation were increased in parallel with increasing concentrations of glycerol or ethylene glycol. These results indicate that the adaptation to these repellents is performed by the demethylation of MCPs. Thus, glycerol and ethylene glycol are novel repellents, which utilize not just one but all three kinds of MCPs for both information processing and adaptation.     

Induced circular dichroism and mode of binding of acridine orange adsorbed on β-form poly(S-carboxyethyl-L-cysteine) in aqueous solutions

The absorption spectra and circular dichroism (CD) have been measured for aqueous solutions of acridine orange of a constant concentration, [D] = 5 × 10^?5M, mixed with poly(S-carboxyethyl-L -cysteine) in various mixing ratios, [P]/[D], ranging from 330 to 11, at different pH. The absorption spectra of the dye–polymer solutions are hypochromic, and the main band is located at 470 nm, accompanying a shoulder at 500 nm. At alkaline pH, no CD is induced in the visible region. At neutral and acidic pH, where the polymer is in the β-conformation, CD is induced in the visible and near-uv regions. A pair of CD bands is located at the region around 450 nm, when the pH is around the neutrality, while it appears at the region around 500 nm at acidic pH. Thus, the optically active species of bound dye changes from dimer to monomer on lowering the pH. These species form dissymmetric arrays along a polypeptide chain. The fraction of bound dye forming dissymmetric sequences is not high, but most of bound dye is adsorbed randomly on the ionized carboxyl groups of polypeptide chain and gives rise to hypochromism only. A dissymmetric structure of dye–polymer complexes is presented, in which the polymer has the β-conformation and the dye cations, either dimeric or monomeric, bind to its side chains, in such a way that the longer axes of molecular planes of bound dye form a two-fold, right-handed helix along the extended polypeptide chain. A zeroth-order calculation of CD based on the coupled oscillator model leads to the result that each dissymmetric array of dye consists, on the average, of two dimeric or monomeric cations. This low number of bound cations in a dissymmetric array and the large fraction of randomly adsorbed dye suggest that the hydrophobic interaction of dye with the polymer is strong, so that dye cations are adsorbed sparsely on both sides of the extended polypeptide chain.     

Quenching of intrinsic tryptophan fluorescence in membranes of rat pituitary cells.

The GH4C1 strain of hormone-producing rat pituitary cells has specific receptors for the tripeptide thyrotropin-releasing hormone (TRH). Membranes prepared from GH4C1 cells show intrinsic tryptophan fluorescence which was quenched by low concentrations (10--100 nM) of TRH and Ntau-methyl TRH but not by biologically inactive analogs of TRH. Membranes from GH4C1 cells were subjected to thermal denaturation. A conformational transition was noted above 40 degrees C and an irreversible denaturation was observed at 52 degrees C. TRH-induced quenching of intrinsic fluorescence was lost completely in membranes previously incubated for 10 min at 30 degrees C while loss of [3H]-TRH binding was only about 20% at this temperature. Collisional quenching by iodide revealed that about 38% of the tryptophanyl residues in GH4C1 membranes were exposed to solvent. Quenching by TRH occurred with a shift in wavelength maximum from 336 to 342 nm suggesting that few of the tryptophanyl residues quenched by the tripeptide are totally exposed. Membranes prepared from cells preincubated with 20 nM TRH for 48 h, in which TRH receptors were decreased to 30% of control values, showed no quenching of tryptophan fluorescence in response to freshly added TRH. We conclude that the TRH-receptor interaction in GH4C1 cells is associated with a change in membrane conformation that can be measured by differential spectrofluorometry of intrinsic tryptophan fluorescence.     

Replication of bacteriophage T4 DNA in vitro. I. Basic properties of the system.

A new in vitro system for T4 DNA replication was developed by concentrating cell lysates on cellophane disks. The time course of [3H]dTTP incorporation into DNA by the system was separated into two phases: one was a very rapid incorporation which was terminated within 2 min (phase I reaction), and the other was a slow but continuous incorporation thereafter (phase II reaction). More than half of the phase I reaction product was Escherichia coli DNA, but the phase II reaction was mostly T4 DNA. Phase II reaction required four deoxyribonucleoside triphosphates, ATP, Mg2+, and KCl. 5-Hydroxymethyldeoxycytidine triphosphate was essential for the reaction and not substitutable by dCTP. The presence of KCN or NaN3 in the reaction mixture did not interfere with [3H]dTTP incorporation, but the addition of deoxyribonuclease completely degraded the system. Alkaline sucrose sedimentation analysis of phage II reaction product revealed that phase II reaction proceeded by the discontinuous mode of DNA replication as in vivo. After T4 infection, the activity for phase II reaction appeared in parallel with the activity of T4 phage DNA replication in vivo.     

Effect of temperature on motility and chemotaxis of Escherichia coli.

The swimming velocity of Escherichia coli at various constant temperatures was found to increase with increasing temperature. The frequency of tumbling had a peak at 34 degrees C and was very low both at 20 and at 39 degrees C. The swimming tracks near the surface of a slide glass showed curves, and the curvature increased the temperature. When the temperature of a bacterial suspension was suddenly changed, a transient change of the tumbling frequency was observed. A temperature drop induced a temporary increase in the tumbling frequency, and a quick rise of temperature, on the other hand, resulted in a temporary suppression of the tumbling. These dynamic responses to sudden changes of temperature was not observed in the smoothly swimming nonchemotactic strains bearing the mutations cheA and cheC and also in a mutant with the metF mutation under a smooth swimming condition.     

Toward more comprehensive environmental impact assessments: interlinked global models of LCIA and IAM applicable to this century

The International Journal of Life Cycle Assessment - Despite the long-standing demand for research on dynamic lifecycle assessment (LCA) for policymaking, only a few studies have addressed this...     

miR-34a-5p might have an important role for inducing apoptosis by down-regulation of SNAI1 in apigenin-treated lung cancer cells

Molecular Biology Reports - Apigenin is a flavonoid with antioxidant and anticancer effects. It has been reported that apigenin inhibits proliferation, migration, and invasion and induces apoptosis...