Electrostatics and gating of excitable membranes

Two electrostatic models for ion permeability of membranes are considered. In the first model ions pass hydrated through the membrane and in the second model ions pass unhydrated through a channel lined with polar groups. In both cases it is found that it is not necessary to assume a high macroscopic dielectric constant of the membrane or channel to provide a low enough potential energy of the ion in the membrane. Gating of excitable membranes is considered a special case of electrostatic interaction in membranes. A simple physical model which fits with Hodgkin and Huxley's empirical relation is derived. Finally, we have speculated upon other membrane bound biological phenomena where electrostatic effects may be important.     

G protein-coupled receptor mediated sensing of TMA

A new approach for the detection of trimethylamine (TMA) using recombinant Xenopus laevis melanophores was developed. The cells were genetically modified to express the mouse trace amine-associated receptor 5 (mTAAR5), a G protein-coupled receptor from the olfactory epithelium, which conferred high sensitivity to TMA. A focused chemical screen allowed the discovery of additional, previously unknown stimuli of mTAAR5. The cell-based sensor demonstrated no sensitivity to trimethylamine N-oxide (TMAO), making it suitable for a convenient evaluation of TMA levels in fish tissue extracts. The developed gas measurement platform was able to detect TMA from 1 to 100 ppm within thirty-five minutes.     

A unified approach to particle-holes and rotations in the spectrum of 16O

The cranked Nilsson-Strutinsky formalism is applied to the many-faceted spectrum of ¹⁶O. The deformation parameters ?, γ and ε₄ are varied independently and many-particle-many-hole excitations are considered in the rotating system. Potential-energy surfaces are presented at different values of spin, parity and signature. Surprisingly good agreement is obtained when the different minima are compared with the measured states. Generally, it is observed that the more particles that are excited to higher shells, the larger becomes the intrinsic deformation. Rotational bands as well as pure p-h excitations, the latter sometimes constituting the termination of a rotational band, are identified. Additional high-spin states (I ? 12) are suggested. A microscopic analysis is performed of the rotational bands which emerge when ¹⁶O in its triaxial 4p-4h configuration rotates around each of its three principal axes.     

Synthesis and reactions of hydroxylated stilbenes and their possible occurrence as chromophore precursor structures in lignin

Chromophores which contribute to the color of kraft lignins and the generation of dihydroxystilbene structures as chromophore precursors are discussed briefly. The various o,p- and p,p-dihydroxystilbenes and 4,4-dihydroxy-3,3-dimethoxy-5-(4-hydroxy-3-methoxystyryl)stilbene, obtained viaWittig syntheses, are colorless substances which become more or less red colored when exposed to air. By reductive acetylation (zinc—acetic anhydride) stilbenoquinones, o- and p-quinonoid, diphenoquinoic, quinone methide, and stable oxygen radical structures are converted to colorless compounds, stabilized by simultaneous blocking of the formed phenolic hydroxyl groups. Application of that reaction to technical kraft lignin fractions let assume that a low number of chromophore structures (max. 5%) are responsible for the intensive color of the material.     

A randomly generated program for automatic identity checking

A method for making secret programs for automatic identity checking with very high demands for security, is described. The consistency of the sequence of digits, which identifies the person, is tested by a sequence of transformations, chosen by means of a stored secret random table. The method has been implemented for a system of unattended cash dispenser terminals, equipped with microprocessors.     

Determination of the structures of symmetric protein oligomers from NMR chemical shifts and residual dipolar couplings

Symmetric protein dimers, trimers, and higher-order cyclic oligomers play key roles in many biological processes. However, structural studies of oligomeric systems by solution NMR can be difficult due to slow tumbling of the system and the difficulty in identifying NOE interactions across protein interfaces. Here, we present an automated method (RosettaOligomers) for determining the solution structures of oligomeric systems using only chemical shifts, sparse NOEs, and domain orientation restraints from residual dipolar couplings (RDCs) without a need for a previously determined structure of the monomeric subunit. The method integrates previously developed Rosetta protocols for solving the structures of monomeric proteins using sparse NMR data and for predicting the structures of both nonintertwined and intertwined symmetric oligomers. We illustrated the performance of the method using a benchmark set of nine protein dimers, one trimer, and one tetramer with available experimental data and various interface topologies. The final converged structures are found to be in good agreement with both experimental data and previously published high-resolution structures. The new approach is more readily applicable to large oligomeric systems than conventional structure-determination protocols, which often require a large number of NOEs, and will likely become increasingly relevant as more high-molecular weight systems are studied by NMR.     

Neighbours of Einstein's equations: Connections and curvatures

Once the action for Einstein's equations is rewritten as a functional of anSO(3, ) connection and a conformal factor of the metric, it admits a family of neighbours having the same number of degrees of freedom and a precisely defined metric tensor. This paper analyzes the relation between the Riemann tensor of that metric and the curvature tensor of theSO(3) connection. The relation is very complicated in general. The Einstein case is distinguished by the fact that two naturalSO(3) metrics on theGL(3) fibres coincide. In the general case the theory is bimetric on the fibres.