Ab initio molecular orbital study of the interaction of Li, Na and K with the pore components of ion channels: Consideration of the size, structure and selectivity of the pore of the channels

Ab initio molecular orbital calculations were made for the various types of structures of the pore of the ion channel and the results were applied to the permeability model by Hille, an extension of the Eyring rate theory. In Hille's model, ion passage through the channel is regarded as a kinetic process. Accordingly, it is thought that the interaction energy between cation and ligand, the easier the passage is, due to the lower activation energy. The calculated interaction energy was in the order Li+ greater than Na+ greater than K+ for all models. The optimum size of the pore determined from the interaction energy depends on the structure of the filter. The size for the pentagon was largest, followed by the hexagon and tetragon. On the other hand, the size depends hardly at all on the kind of ligand molecules. In the case of the tetragon, the sizes for the Na and K channels were nearly the same as those estimated from the model building and inhibitor-blocking experiment. The interaction energy between the ionized carboxyl group and the cation was extremely large, clearly reflecting the experimental fact that the carboxyl group in the pore has an important role in making the passage of the cation through the channel easier by dehydrating the water molecules. By analysis of the interaction energy, it was revealed that the contribution of the electrostatic energy was predominant, although the contributions of the other effects might not be negligible. Among these effects, the value of the charge transfer energy is largest, and this is noteworthy in connection with the selective transmission of cations through the overlap of orbitals. It is concluded that the quantum-chemical indices such as interaction energy and the electronic charge calculated by the sophisticated ab initio method help to shed light on the nature of the pore of the ion channel.     

Glucose/molasses effects on enzyme activities and fermentative activity of fully aerobic continuous cultures of baker’s yeast

Supplementing a molasses medium with glucose was expected to have deleterious effects on the quality of industrially grown baker’s yeast. This was investigated in the laboratory using beet molasses and glucose in fully aerobic continuous cultures of baker’s yeast.     

Establishment of a strain inheriting a sex-linked SNP marker in Patagonian pejerrey (Odontesthes hatcheri), a species with both genotypic and temperature-dependent sex determination

The Patagonian pejerrey Odontesthes hatcheri is an atherinopsid species presenting genotypic sex determination (GSD) at intermediate temperatures and temperature-dependent sex determination at the low and high ranges of thermal tolerance. A recent study revealed the presence of a sex-linked SNP marker in some males of this species, but a strain which inherits the marker faithfully has not been established. This research was conducted to develop such a strain, for use as a tool to study the molecular mechanisms of gonadal sex differentiation and sexual dimorphism, and to obtain basic information on the GSD mode in this species. For these purposes, we performed backcrosses and full-sibling crosses using males and females whose presumptive genotypic sex was inferred from the presence of the sex-linked SNP marker. Four backcrosses between SNP⁻ daughters and their SNP⁺ father generated balanced sex ratios with the phenotypic sex matching the genotypic sex in most cases (98.21%) at an intermediate, sexually neutral temperature (21 °C). Full-sibling crosses between these four SNP⁻ females and their SNP⁺ brothers produced three progenies with balanced sex ratios and one with 94.4% males. The results of this study confirm that a strain inheriting the sex-linked SNP marker was successfully developed. Moreover, the inheritance pattern of the marker and the sex ratios of the progenies provide strong evidence that the GSD mode in O. hatcheri is the XX–XY system.     

The Candida glabrata sterol scavenging mechanism,mediated by the ATP‐binding cassette transporter Aus1p,is regulated by iron limitation

During disseminated infection by the opportunistic pathogen Candida glabrata, uptake of sterols such as serum cholesterol may play a significant role during pathogenesis. The ATP‐binding cassette transporter Aus1p is thought to function as a sterol importer and in this study, we show that uptake of exogenous sterols occurred under anaerobic conditions in wild‐type cells of C. glabrata but not in AUS1‐deleted mutant (aus1Δ) cells. In aerobic cultures, growth inhibition by fluconazole was prevented in the presence of serum, and AUS1 expression was upregulated. Uptake of sterol by azole treated cells required the presence of serum, and sterol alone did not reverse FLC inhibition of growth. However, if iron availability in the growth medium was limited by addition of the iron chelators ferrozine or apo‐transferrin, growth of wild‐type cells, but not aus1Δ cells, was rescued. In a mouse model of disseminated infection, the C. glabrata aus1Δ strain caused a significantly decreased kidney fungal burden than the wild‐type strain or a strain in which AUS1 was restored. We conclude that sterol uptake in C. glabrata can occur in iron poor environment of host tissues and thus may contribute to C. glabrata pathogenesis.