Topological information content and chemical reactions

The difference of the topological information content of two reacting molecules and that of their reaction products is calculated for several topological types of chemical reactions, illustrating the influence of the structure of the reagents and of the reaction product. It is shown that the change in the topological information content in a chemical reaction can be positive as well as negative, depending on the way the reagents approach each other and thus on the reaction product formed. A quantitative measure of structural specificity is introduced.     

Agmenellum quadruplicatum M.AquI, a novel modification methylase.

The complete type II modification methylase of Agmenellum quadruplicatum was cloned in Escherichia coli as an R.Sau3A fragment of approximately 4.5 kilobases. The coding sequence was contained in a stretch of 1,156 base pairs which was organized into two parallel, partly overlapping open reading frames of 248 and 139 codons. In vivo complementation experiments showed that the synthesis of both predicted peptides was required for full methylase activity. The amino acid sequences were considerably similar to regions of other deoxycytidylate methylases.     

On spontaneous discharge obtained from a physicochemical model of excitation

It is shown that a slight modification of a model of excitatory phenomena in irritable tissues, which has been treated before, exhibits spontaneous oscillations. The frequency of these oscillations and the time-course of the potential across the model membrane have been determined, together with the dependence of some of their characteristics on some important parameters, particularly (Ca⁺⁺).     

Electrical potentials and ionic fluxes in ion exchangers: I. “n type” non-ideal systems with zero current

In this paper a derivation, based on the Nernst-Planck flux equations extended for non-ideal behavior, is given for the electrical potentials and cationic fluxes occurring across a one-phase ion exchange system separating two aqueous solutions. It is assumed that the activities of the cations in the exchanger are proportional to thenth power of their concentrations, a relationship of broad empirical validity. This paper deals only with the case of the quasi-stationary state in which no net electrical current flows. The profles of the cationic concentrations and of the diffusion potential in the exchanger are found to be, in general, exponential and linear respectively. An equation is derived for the stationary-state potential of an ion exchange phase interposed between two aqueous solutions containing mixtures of two cations. The potential selectivity constant of this equation is found to equal the product of the ion exchange equilibrium constant and thenth power of the mobility ratio.     

Adsorption of ions at charged sites and phase boundary potentials

The Poisson equation is used to determine for the equilibrium case the space profile of the electric potential at the boundary of two phases, one of which contains anionic sites able to adsorb selectively available cations. The solution has given an expression for the effective width of the space profile of the phase boundary potential in terms of the concentrations and the adsorption characteristics of the ions. It is shown that the sign of one (lumped) parameter determines the sign of the potential. It is also shown that a value of 66 Å can be obtained for the effective width of the space profile of the phase boundary potential. The implications concerning the nature of the “membrane” are briefly discussed.     

Contributions to quantum biology. I. Mobile electronic characteristics of riboflavin radicals

Quantum biology is the quantum mechanical study of electrons in molecules of biological interest. This requires the solution of problems involving many electrons. Approximation methods are therefore necessary and are discussed. The present study, concerned with the mobile electrons in riboflavin (FMN) and its radicals (FMN⁻, FMNH and FMNH₂ ⁺), is based on the approximation method, developed by B. Pullman and A. Pullman. The solution of the eigenvalue problems so obtained gives the energy levels of the mobile electron systems involved. The corresponding eigenvectors yield the mobile electronic charges of the atoms of riboflavin radicals which have contributed mobile electrons. Important differences of the net charge distributions of these radicals are emphasized. The longest wave length of light absorption is calculated from the obtained energy levels and agrees, within the accuracy of the method, with corresponding experimental results. From the appropriate calculated results, electronic assignments are obtained for the experimental transitions involved.     

New positive/negative selectable markers for mammalian cells on the basis of Blasticidin deaminase-thymidine kinase fusions.

Two positive and negative selectable markers were created for use in mammalian cells. They are based on two genes for the resistance to Blasticidin S (BlaS) and on the thymidine kinase (Tk) gene of herpes simplex virus (HSV). The markers can be selected positively by their ability to induce BlaS resistance and negatively on the induced sensitivity towards gancyclovir (GANC). Both constructs are also expressed in Escherichia coli and transfer BlaS resistance to this organism as well, making these markers very suitable for the construction of shuttle vectors.     

The stress response protein Hsp12p increases the flexibility of the yeast Saccharomyces cerevisiae cell wall

The yeast S. cerevisiae cell wall comprising a 10 nm thick layer of polysaccharides, predominantly beta(1,3)-glucan and proteins, is the interface between the cell and the neighbouring environment. As such it is not a static entity but rather one that is dynamically remodelled in response to changes in the environmental conditions. We have recently proposed from studies using yeast cells lacking the gene encoding Hsp12p (Deltahsp12 yeast) and from incorporation of Hsp12p into agarose, used as a model system for the beta-glucan layer of the cell wall, that the hydrophilic stress response cell wall protein Hsp12p acts as a cell wall plasticizer. In this report we have used force spectroscopy to confirm that Deltahsp12 yeast are indeed less flexible than the wild type strain. The spring constant of the cell wall of Deltahsp12 yeast, kcw was determined to be 72+/-3 mN m-1 as compared to 17+/-5 mN m-1 obtained for the wild type strain. A similar result was found on the basis of a quantitative analysis of the electrophoretic mobilities measured for the two yeast strains. Those indicated that the hydrodynamic permeability quantified through the softness parameter of the external layer of Deltahsp12 cells was smaller than the one of wild type cells. We proposed from surface infrared spectroscopy measurements that yeast compensate for the lack of Hsp12p by reducing the carbohydrate/proteins ratio of the cell wall or increasing the cell wall chitin content.     

Modulation of Congo-red-induced aberrations in the yeast Saccharomyces cerevisiae by the general stress response protein Hsp12p

Previous studies have shown that in Saccharomyces cerevisiae HSP12, which codes for the small cell wall heat shock protein Hsp12p, was induced upon exposure to cell-wall-damaging agents such as Congo red. Here, we demonstrate that Hsp12p decreases the interaction between Congo red and chitin. A Deltahsp12 mutant strain displayed decreased viability, increased aggregation and sedimentation, as well as an altered morphology when grown in the presence of Congo red dye. The presence of Hsp12p was also necessary for the Congo-red-mediated invasion of agar plates.     

Unexpected overdose with diltiazem: value of toxicological screening

We describe a 59-year-old woman who was admitted in deep coma with bradycardia, hypotension and fixed pupils. The cause of her severe condition was unclear. Cerebral and myocardial infarction was excluded. Temporary transcutaneous pacing was not successful, nor was atropine or norepinephrine (noradrenaline), but the patient responded well to isoprenaline infusion. Since she was known to have a psychiatric history, toxicological screening was performed which showed a severe diltiazem overdose. Later we discovered that she took diltiazem for angina pectoris. The patient survived and was discharged without neurological or cardiological deficits after two days of treatment. This case report emphasises the importance of toxicological screening in unconscious patients with no apparent cause. We review the clinical features and treatment options of diltiazem overdose and discuss the value of toxicological screening.