Uptake of methionine sulfoximine by some N2 fixing bacteria, and its effect on ammonium transport

The N2 fixing bacteria Klebsiella pneumoniae, Azospirillum brasilense, Rhodopseudomonas sphaeroides and Rhodospirillum rubrum, but not Azotobacter vinelandii accumulate the glutamine analogue methionine sulfoximine in the cell. In the accumulating cells methionine sulfoximine inhibits ammonium transport. Accumulation and inhibition are prevented by glutamine.     

Rates and equilibria at the acetylcholine receptor of electrophorus electroplaques. A study of neurally evoked postsynaptic currents and of voltage-jump relaxations

Kinetic measurements are employed to reconstruct the steady-state activation of acetylcholine [Ach] receptor channels in electrophorus electroplaques. Neurally evoked postsynaptic currents (PSCs) decay exponentially; at 15 degrees C the rate constant, α, equals 1.2 ms(-1) at 0 mV and decreases e-fold for every 86 mV as the membrane voltage is made more negative. Voltage-jump relaxations have been measured with bath-applied ACh, decamethonium, carbachol, or suberylcholine. We interpret the reciprocal relaxation time 1/τ as the sum of the rate constant α for channel closing and a first-order rate constant for channel opening. Where measureable, the opening rate increases linearly with [agonist] and does not vary with voltage. The voltage sensitivity of small steady-state conductances (e- fold for 86 mV) equals that of the closing rate α, confirming that the opening rate has little or no additional voltage sensitivity. Exposure to α-bungarotoxin irreversibly decreases the agonist-induced conductance but does not affect the relaxation kinetics. Tubocurarine reversibly reduces both the conductance and the opening rate. In the simultaneous presence of two agonist species, voltage-jump relaxations have at least two exponential components. The data are fit by a model in which (a) the channel opens as the receptor binds the second in a sequence of two agonist molecules, with a forward rate constant to 10(7) to 2x10(8) M(-1)s(-1); and (b) the channel then closes as either agonist molecule dissociates, with a voltage-dependent rate constant of 10(2) to 3x10(3)s(-1).     

Relationships between nitrogenase,glutamine synthetase,glutamine, and energy charge in Azotobacter vinelandii

When continuous cultures of Azotobacter vinelandii were supplied with ammonium or nitrate in amounts, which just repressed nitrogenase synthesis completely, both the intracellular glutamine level and the degree of adenylylation of the glutamine synthetase (GS) increased only slightly (from 0.45–0.50 mM and from 2 to 3 respectively), while the total GS level remained unaffected. Higher amounts of ammonium additionally inhibited the nitrogenase activity, caused a strong rise in the intracellular glutamine concentration and adenylylation of the GS, but caused no change in the ATP/ADP ratio. These results are considered as evidence that in A. vinelandii the regulation of nitrogenase synthesis is not linked to the adenylylation state of the GS and to the intracellular glutamine level, and that the inhibition of the nitrogenase activity as a consequence of a high extracellular ammonium level is not mediated via a change in the energy charge.Abbreviations GS glutamine synthetase - GS-S(Mg) Mg²⁺ dependent synthetic activity of GS - GS-T(Mn) Mn²⁺ dependent transferase activity of GS     

Relative levels of guanosine 5′-diphosphate 3′-diphosphate (ppGpp) in some N2 fixing bacteria during derepression and repression of nitrogenase

Addition of ammonium to N₂ fixing cultures of Azotobacter vinelandii, Klebsiella pneumoniae and Clostridium pasteurianum rapidly reduced the intracellular levels of guanosine 5-diphosphate 3-diphosphate (ppGpp) by 70–90%. This change might reflect a regulatory role of ppGpp in nitrogen metabolism.Abbreviations ppGpp guanosine 5-diphosphate 3-diphosphate     

Activities of Various Peptidases in the First Leaf of Wheat

In the first leaf of wheat (Triticum aestivum L. cv. Capelle) the content of soluble protein diminished to about 50% of the initial value between the 7th and the 19th day after sowing. In order to understand proteolysis in the leaves, the activities of several peptidases were measured in extracts from leaves at four different ages. The carboxypeptidase activities increased during the growth of the leaves, and then began to decrease. The activities of the alkaline peptidases increased, while that of the benzoyl-DL-arginine-p-nitroanilide (BAPA) hydrolysing enzyme decreased during the whole period studied. The “naphthylamidase” activities showed first a slow rise, but then leveled off. Two bands with naphthylamidase activity could be detected after disc electrophoresis. All the peptidases studied were present in the leaves at rather high concentrations. This indicates that they all may participate in the hydrolysis of leaf proteins into free amino acids.     

Study on conformational states of Escherichia coli tRNAPhe in solution by a modulation-free ESR-spectrometer

A modulation free Electron Spin Resonance spectrometer was used for the registration of spectral absorption lines of a spin-labeled Escherichia coli phenylalanine tRNA in solution with low (less than 0.1%) line shape distortion. The analysis of line shape of two different spin-labels introduced into position 8 revealed that phenylalanine tRNA in solution exists as a mixture of two conformers, the equilibria between conformers being dependent on pH, concentration of magnesium and functional state of tRNA (deacylated, aminoacylated or peptidylated). There are no overall structural rearrangements upon aminoacylation or peptidylation of tRNA. The observed small changes of spectral line shape can be assigned to shifts in conformational equilibria.     

INSULIN PRODUCES A BIPHASIC RESPONSE INTETRAHYMENA THERMOPHILABY STIMULATING CELL SURVIVAL AND ACTIVATING PROLIFERATION IN TWO SEPARATE CONCENTRATION INTERVALS

Cells ofTetrahymenamay produce autocrine signal molecules with effects on survival and proliferation. Here we have tested the effects of human recombinant and bovine insulin, and the B22–B30 fragment of bovine insulin over a wide range of concentrations (10^?5–10^?18m ) on cell survival and proliferation in a synthetic nutrient medium. The cells were grown in conical flasks at low initial cell densities (40 and 400cells/ml). Insulin prevented rapid cell death and/or promoted cell proliferation over two separate concentration ranges: down to nanomolar levels and again in the low pico- and femtomolar range. At an initial population density of 400cells/ml the cells multiplied at both concentration intervals. At 40 or fewer organisms/ml the cells multiplied in the high concentration interval, whereas in the low interval they survived for about four times longer than those in the control cultures. B22–B30 added to cultures of 40 initial cells/ml produced a stimulation of cell survival in the low pico- and high femtomolar range. In the presence of hemin (50nm ) cells at 400 initial organisms/ml multiplied at insulin concentrations down to about 3nm and again from 300am to 10pm . In some cases, hemin plus insulin activated cell proliferation between the two concentration intervals as well. At 40cells/ml the cells not only survived but proliferated in the femtomolar range. Cells in cultures supplemented with both hemin and B22–B30 multiplied at the low concentration interval (from about 100fm to 10pm ).     

Sixty simple sequence repeat markers for use in the Festuca–Lolium complex of grasses

So far only very few simple sequence repeat (SSR) markers developed from grass species have had their primer sequences published. To make more markers available to the scientific community, we isolated and sequenced 256 microsatellite‐containing clones from four genome libraries of a Lolium multiflorum×Festuca glaucescens F₁ hybrid following enrichment in (TC)_n, (TG)_n, or both repeats. In this work, we report the primer sequences of 60 SSRs including preliminary results of polymorphism for mapping.     

The effect of Zn2+ ions on mitochondrial electron transport

Zn²⁺ ions linearly inhibit the electron transport in uncoupled mitochondria, Mg²⁺/ATP submitochondrial particles, and electron transport complex III between ubiquinone and the b cytochromes. A second effect is observed in coupled mitochondria only, where less than 4 μm Zn²⁺ causes a respiratory stimulation and a reduction of the b cytochromes; higher concentrations reverse these effects. The inhibition is completely reversed by chelating agents. The binding site has a unique affinity for Zn²⁺ with a dissociation constant of 1·10^?6.