Kinetic analysis of product release and metal ions in a metallonuclease

Most nucleases rely on divalent cations as cofactors to catalyze the hydrolysis of nucleic acid phosphodiester bonds. Here both equilibrium and kinetic experiments are used to test recently proposed models regarding the metal ion dependence of product release and the degree of cooperativity between metal ions bound in the active sites of the homodimeric PvuII endonuclease. Equilibrium fluorescence anisotropy studies indicate that product binding is dramatically weakened in the presence of metal ions. Pre-steady state kinetics indicate that product release is at least partially rate limiting. Steady state and pre-steady state data fit best to models in which metals remain bound to the enzyme after the release of product. Finally, analysis of cooperative and independent binding models for metal ions indicates that single turnover kinetic data are consistent with little to no positive cooperativity between the two metal ions binding each active site.     

Stimulation of carotenogenesis in Blakeslea trispora by cupric ions

Growth of mated Blakeslea trispora in the presence of trace amounts of cupric ions resulted in increases in (a) the amount and rate of initiation of carotenogenesis, (b) the utilization of glucose and Pi and (c) growth. It also caused an increase in trisporic acid synthesis and a two-fold increase in mevalonate kinase activity.     

Potential-dependent phase partitioning of fluorescent hydrophobic ions in phospholipid vesicles

Summary Fluorescent, dansyl derivatives of triphenylalkylphosphonium ions have been synthesized and exhibit fluorescence intensities in small sonicated phospholipid vesicles that are dependent upon transmembrane potentials. The voltage-dependent fluorescence changes are a result of changes in quantum yield that accompany a voltage-dependent phase partitioning of the probe. This phase partitioning is easily quantitated by calibrating the intensities of totally membrane-associated and aqueous probe. The voltage-dependence is well accounted for by a simple thermodynamic model and allows an estimation of potentials from fluorescence intensities in small vesicle systems.     

Sorption of anionic polysaccharides by cellulose

The sorption of anionic polysaccharides pectin, alginate, and xanthan with cellulose were investigated in presence of calcium. Calcium sorption to cellulose was limited by the carboxyl group content in fibers. Atomic Absorption Spectroscopy (AAS) analysis was used to measure the calcium in cellulose fibers and chemical oxygen demand (COD) analysis reveals that the divalent ions calcium can bind the polysaccharide onto cellulose fibers. The amount of calcium and polysaccharide bound in Ca²⁺/polysaccharide modified cellulose fibers was 5.8-12.5 mM Ca²⁺/kg fibers and 1500-2400 mg polysaccharide/kg fibers, respectively. Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance (FTIR-ATR) analysis confirmed the presence of polysaccharide on calcium containing cellulose fibers. The results of alizarin dyeing experiments at the end of polysaccharide sorption further confirmed the presence of calcium in Ca²⁺/polysaccharide modified cellulose fibers. The basic phenomenon of interaction of soluble ionic polysaccharide and cellulosic fibers in presence of divalent cations such as calcium is a key to understand biological functions and technological applications.     

Genome‐wide association study identifies loci linked to serum electrolyte traits in Chinese Holstein cattle

We aimed to identify QTL for serum electrolyte traits by performing a GWAS of calcium, chloride, sodium, potassium and magnesium ion concentrations in Chinese Holstein cattle. We detected five SNPs that had significant associations with calcium ion concentrations and identified GATA2 from Bos taurus chromosome (BTA)22 as having the highest significance. Among the genes with significant results, we speculate that TMEM123 might be related to calcium channel proteins according to the functions of the TMEM family.     

Induction of phenolic compounds in two dark-grown lentil cultivars with different tolerance to copper ions

The influence of a high copper sulphate concentration on growth, Cu accumulation, lipid peroxidation as well as on the contents of total phenolic compounds (PhC) and UV-absorbing compounds (UVAC) in roots of lentil (Lens culinars Medic.) cvs. Krak and Tina was investigated. The plants were subjected to 0.5 mM Cu²⁺ for 3 and 5 days in darkness. Growth inhibition and increased lipid peroxidation in the roots of both cultivars, especially in cv. Tina which accumulated more Cu, were observed. Cu²⁺ treatment caused greater PhC and UVAC accumulation in cv. Krak; however, constitutive levels of these compounds were higher in cv. Tina. The maximum absorption peak of UVAC was determined at 270 nm. HPLC analyses of these compounds revealed the presence of two main derivatives of the soluble (aglycone and ester-bound) fraction of the hydroxycinnamic acids, ferulic (FA) and p-coumaric (p-CA) acids and the flavonol, kaempferol (Kam). Greater changes in the content of phenolic acids than of Kam may suggest that the former play a more important role in protecting lentil roots against high Cu²⁺ concentration. Thus, while the lower PhC levels at a higher Cu content in the roots of cv. Tina were probably due to stress, their higher levels in cv. Krak could have been a response to ROS signaling. However, though the high concentration of Cu²⁺ stimulated PhC in cv. Krak, it was not sufficient to counteract the amount of ROS generated by metal presence. These observations may suggest that ROS can serve as a common signal for acclimation to Cu²⁺ stress and cause PhC accumulation in dark-grown roots. The role of PhC in lentil tolerance to Cu²⁺ stress is discussed.     

Influence of bicarbonate and metal ions on the development of root Fe(III) reducing capacity by Fe-deficient cucumber (Cucumis sativus) plants

The effect of bicarbonate and selected metal ions on the development of enhanced root Fe(III) reducing capacity (a response to Fe deficiency of dicotyledons) was studied in young plants of cucumber ( Cucumis sativus L. cv. Ashley) grown in nutrient solution. Pretreatment of 11-day-old Fe-deficient cucumber plants with 20 m M NaHCO₃, for at least 23 h prior to determination of root Fe(III) reducing capacity, markedly inhibited this response. The inhibitory effect of bicarbonate could be partly reversed by a 4- to 8-h treatment with either 10 μ M MnSO₄, 10 μ M FeEDDHA, 2 μ M ZnSO₄, 0.5 μ M NiCl₂, or 0.25 μ M , or CoSO₄ (final concentrations), added to the nutrient solution. By contrast, the addition of other salts of metal ions, like CuSO₄ and Cd(NO₃)₂, at 0.25, 0.5 or 1 μ M , or MgSO₄, at 0.5, 1 or 2 m M (final concentrations), had no beneficial effect. The results suggest that bicarbonate may inhibit the development of root Fe(III) reducing capacity by diminishing the availability of certain metal ions required for this response.     

Induction of calcium-ion efflux from brain tissue by radiofrequency radiation: Effect of sample number and modulation frequency on the power-density window

Changes have been found in calcium-ion binding to brain tissue exposed in vitro to a specific power density (0.83 mW/cm²) of 147-MHz radiation, amplitude modulated by a 16-Hz sine wave. This report replicates and extends this previous work. To define more precisely the range of effective power densities, two different numbers of samples were treated in a Crawford cell. In one series, four brain tissues were exposed at a time; in the other series, four brain tissues plus six dummy loads were exposed together. While the four-sample configuration produced a narrow power-density window, the ten pseudosample configuration resulted in a broader power-density window. The reason for the sample-number dependence is unresolved, but may be due to interactions between samples and field distortions caused by the close spacing. The ten pseudosample configuration was used to test for the presence and range of a power-density window at a sinusoidal modulation frequency of 9 Hz. The response curve at 9 Hz was essentially identical to the results for 16-Hz sinewave modulation.