Surface properties of plasma membrane vesicles isolated from melon (Cucumus melo L.) root cells differing in salinity tolerance

The hypotheses that genotypic differences in salinity tolerance may result from (i) differences in global surface charge density or (ii) from differences in global Ca²⁺ binding were tested. An attempt was made to correlate the differing salinity tolerance of four melon cultivars with surface properties of vesicles extracted from the plasma membrane (PM) of their root cells. Surface characterization involved measurements of electrophoretic mobility and sorption of ⁴⁵Ca²⁺ to the vesicles in the presence of varying concentrations of Ca²⁺, Na⁺ and Mg²⁺. Irrespective of salinity tolerance, vesicles from the four cultivars yielded similar ζ potentials under similar conditions, indicating similar global surface charge densities. Sorption studies with vesicles from two cultivars differing in salinity tolerance predicted independently this result of equal surface charge density. The estimated global binding affinities of Ca²⁺, Na⁺ and Mg²⁺ to the PM of both cultivars were the same with binding coefficients of 50, 0.8 and 9 M⁻¹, respectively. Consequently, the hypotheses enumerated above to interpret genotypic differences in salinity toxicity are rejected. However, vesicles from the salt-resistant strain sorbed 19% more Ca²⁺ per given amount of protein in the membrane, indicating the existence of a larger number of negatively charged surface sites per given amount of protein and a smaller amount of protein per given area of membrane. Genotypic differences in site-specific Ca²⁺-binding affinity (e.g. at ion channels) remain a viable hypothesis for genotypic differences in salinity tolerance.     

Multi-tiling and Riesz bases

Let S   be a bounded, Riemann measurable set in R^d${\mathbb{R}}^d$, and Λ be a lattice. By a theorem of Fuglede, if S   tiles R^d${\mathbb{R}}^d$ with translation set Λ, then S has an orthogonal basis of exponentials. We show that, under the more general condition that S multi-tiles  R^d${\mathbb{R}}^d$ with translation set Λ, S has a Riesz basis of exponentials. The proof is based on Meyer?s quasicrystals.     

Entropy Theory for Cross-Sections

We define the notion of entropy for a cross-section of an action of continuous amenable group, and relate it to the entropy of the ambient action. As a result, we are able to answer a question of J.P. Thouvenot about completely positive entropy actions.     

Azapeptide activity-based probes for the SARS-CoV-2 main protease enable visualization of inhibition in infected cells

The COVID-19 pandemic has revealed the vulnerability of the modern, global society. With expected waves of future infections by SARS-CoV-2, treatment options for infected individuals will be crucial in order to decrease mortality and hospitalizations. The SARS-CoV-2 main protease is a validated drug target, for which the first inhibitor has been approved for use in patients. To facilitate future work on this drug target, we designed a solid-phase synthesis route towards azapeptide activity-based probes that are capped with a cysteine-reactive electrophile for covalent modification of the active site of M^pro. This design led to the most potent ABP for M^pro and one of the most potent inhibitors reported thus far. We demonstrate that this ABP can be used to visualize M^pro activity and target engagement by drugs in infected cells.

The COVID-19 pandemic has revealed the vulnerability of the modern, global society.     

Molecular geometries and moments from the maximum overlap criterion

The maximized overlap population, defined as Σ_μ≠νP_μνS_μν, and a related quantity, Σ_μ,νP_μνS²_μν are computed for a series of configurations. The extremum of both approximate molecular geometries, the latter with an accuracy suitable for predictive value. The maximum overlap orbitals predict dipole and quadrupole moments that give reasonable agreement with experimental values.     

Geometric doppler effect: spin-split dispersion of thermal radiation

A geometric Doppler effect manifested by a spin-split dispersion relation of thermal radiation is observed. A spin-dependent dispersion splitting was obtained in a structure consisting of a coupled thermal antenna array. The effect is due to a spin-orbit interaction resulting from the dynamics of the surface waves propagating along the structure whose local anisotropy axis is rotated in space. The observation of the spin-symmetry breaking in thermal radiation may be utilized for manipulation of spontaneous or stimulated emission.     

Dynamics and morphology of microvilli driven by actin polymerization

Many different cell types have dynamic protrusions, called microvilli, on their surface. We model these structures as arising from the balance between the force of actin polymerization and the restoring force of the membrane. From this simple model we calculate the distribution function of microvilli heights for several cells. We further describe the phase diagram and the resulting morphology of the microvilli aggregates on the cell surface.     

Automatic locking of a parametrically resonating,base-excited,nonlinear beam

Nonlinear Dynamics - Described is a closed-loop control scheme capable of stabilizing a parametrically excited nonlinear structure in several vibration modes. By setting the relative phase between...     

The role of point defects in melting of solid He

We have recently observed that the resistance to shear of solid ⁴He decreases dramatically near the first-order BCC–HCP transition. In our view, the solid shears via a diffusive counter-flow of atoms and point defects. The mechanism of self diffusion couples point defects with one specific phonon which softens as the transition is approached. Since such a scenario can possibly lead to melting, it is important to understand (a) which type of point defect is associated with the reduction of shear resistance, and (b) can the presence of point defects lead to the softening of phonons. We report here the results of numerical simulations and analytic modeling. Our results indicate that split interstitials are much more effective than vacancies in lowering the resistance to shear. We suggest that these excitations can be generated as a result of a “local mode” excited in the crystal.     

Non-covalent Surface Interactions between Silicone and Biological Macromolecules Yield Bioreactive Substances

While most organometallics enter the en- vironment through their industrial release, silicones are organometallic compounds purposefully introduced in high volume directly into healthy humans. A chemically centered study of the behavior of silicones in the biological environment reveals numerous de- gradative reactions and surface interactions that can produce bioreactive substances. Data from a variety of disciplines suggest that the preponderance of evidence supports the argument that silicone is a toxic organometallic. © 1997 by John Wiley & Sons, Ltd.