Molecular dynamics approach to understand the denaturing effect of a millimolar concentration of dodine on a λ-repressor and counteraction by trehalose

Here, we use a molecular dynamics approach to calculate the spatial distribution function of the ternary water–dodine–trehalose (1.0 M) system.

Study of the coordination of quinuclidine to a chiral zinc phthalocyanine dimer

We attempted the calculation of an accurate equilibrium constant for the dimerization process of enantiomerically pure Zn-1 using UV-vis dilution experiments. At millimolar concentration Zn-1 is involved in a chemical exchange process between its monomeric and dimeric state that is slow on the 1H NMR timescale. We performed variable-temperature 1H NMR experiments in CDCl3 solution to determine the dimerization constant value at different temperatures and performed a van’t Hoff plot to derive the thermodynamic parameters of the process. The calculated thermodynamic data revealed that the dimerization process is entropy-driven and enthalpically opposed. We also probed the coordination of quinuclidine, 1-azabicyclo[2.2.2]octane, 2, to the Zn-1 using UV-vis and 1H NMR titrations in CDCl3 solution. At micromolar concentration the Zn-1 exclusively exists in solution as a monomer and forms a simple 1:1, [Formula: see text], complex with quinuclidine having a stability constant of [Formula: see text]([Formula: see text]) [Formula: see text] 106 M[Formula: see text]. On the other hand, the 1H NMR titrations carried out at 298 K and at millimolar concentration showed that Zn-1 was present in solution as the dimer and formed 1:2, [Formula: see text], and 2:2, [Formula: see text] complexes by coordination to 2. In addition, the 1:1 complex, [Formula: see text] showed a reduced dimerization constant compared to the uncoordinated parent monomer Zn-1. At high quinuclidine concentration, the 1:1 complex, [Formula: see text], derived from the coordinated dimer dissociation was also detected. The 1H NMR spectra of the titrations displayed separate signals for some hydrogen atoms of the Zn-phthalocyanine in each one of the four species. Remarkably, the chemical exchange processes involving free and bound quinuclidine in the monomeric and dimeric complexes showed different kinetics on the NMR timescale.

Effect of Aquo-glycolic Media and Added Anions on the Anodization of Zircaloy-4 in Sulphamic Acid

Anodization of zircaloy-4 in 0.1 M sulphamic acid has been carried out. Kinetics of anodic oxidation of zircaloy-4 has been studied at a constant current density of 8 mA/cm2and at room temperature. Thickness estimates were made from capacitance data. The plots of formation voltagevs. time, reciprocal capacitancevs. time, reciprocal capacitancevs. formation voltage and thicknessvs. formation voltage were drawn and rate of formation, current efficiency and differential field were calculated. The addition of solvent (ethylene glycol) showed better kinetic results. For 25%, 50% and 75% aquo-glycolic media, the dielectric constant values are low leading to a marked improvement in the kinetics. In 80% ethylene glycol, though the dielectric constant value of solution is less, the kinetics was slow which may be attributed to the fact that the electrolyte becomes highly non-polar. Improvement in the kinetics of oxide film formation was observed by the addition of millimolar concentration of anions (CO32-, SO42-, PO43-). The presence of phosphate ions improved the kinetics of anodization to better extent.

Effects of Grape Berry Developmental Stages on Ammonium Nitrate-enhanced Penetration of Gibberellin A3

The effects of ammonium nitrate (AMN) on the penetration of Gibberellin A3 (GA3) into berries of `Kyoho' (Vitis labruscana Bailey) grape during berry development were studied. Treatment solutions of GA3 (100 ng·μL-1) and GA3 + AMN (20 millimolar concentration) were applied to the surface of grape berries under field conditions. The amount of GA3 penetrated was assayed using dwarf rice (Oryza sativa L., cv. Tan-ginbozu). At full bloom, the addition of AMN significantly enhanced GA3 penetration 24, 48 ad 72 hours after application by 13%, 16% and 21% of the applied GA3, respectively, representing a 1.7- to 2.4-fold increase over GA3 alone. At 4 weeks after full bloom (WAFB) at 24 hours after application, 20% of the applied GA3 penetrated in the presence of AMN compared to 15% in the absence of AMN. From varaison (7 WAFB) to maturity (10 WAFB), GA3 penetration decreased, from 6% to 2%, respectively, in the presence of AMN, and from 3% to 1% in the absence of AMN. The addition of AMN to the GA3 solution increased GA3 penetration relative to GA3 alone at all berry developmental stages. On the other hand, Cuticular wax density on the berry surface at 4 WAFB was 1.10 μg·mm-2, 5.8-fold greater than at full bloom (0.19 μg·mm-2). The thickness of the epidermal tissue doubled during the first 2 WAFB, but was maintained almost constant over the next 6 weeks. GA3 penetration was more closely related to the cuticular wax levels than the epidermal tissue thickness.

Bi-site activation occurs with the native and nucleotide-depleted mitochondrial F1-ATPase

Experiments are reported on the uni-site catalysis and the transition from uni-site to multi-site catalysis with bovine heart mitochondrial F1-ATPase. The very slow uni-site ATP hydrolysis is shown to occur without tightly bound nucleotides present and with or without Pi in the buffer. Measurements of the transition to higher rates and the amount of bound ATP committed to hydrolysis as the ATP concentration is increased at different fixed enzyme concentrations give evidence that the filling of a second site can initiate near maximal turnover rates. They provide rate constant information, and show that an apparent Km for a second site of about 2 μM and Vmax of 10 s-1, as suggested by others, is not operative. Careful initial velocity measurements also eliminate other suggested Km values and are consistent with bi-site activation to near maximal hydrolysis rates, with a Km of about 130 μM and Vmax of about 700 s-1. However, the results do not eliminate the possibility of additional ‘hidden’ Km values with similar Vmax:Km ratios. Recent data on competition between TNP-ATP and ATP revealed a third catalytic site for ATP in the millimolar concentration range. This result, and those reported in the present paper, allow the conclusion that the mitochondrial F1-ATPase can attain near maximal activity in bi-site catalysis. Our data also add to the evidence that a recent claim, that the mitochondrial F1-ATPase does not show catalytic site cooperativity, is invalid.