Threshold stimulation and accommodation of the Hodgkin-Huxley axon.

The charge-duration and strength-duration relations for just threshold rectangular stimuli were numerically investigated for the Hodgkin-Huxley axons of different lengths and different membrane capacitances under normal conditions and blockage of the development of accommodative processes. Two linear portions could be distinguished on the charge-duration curve. One of them followed the Weiss law. The other one represented a portion of a straight line passing through the zero point of the coordinates. The slope of the second portion was determined by the charge for very short stimuli (Q0), the slope of the first portion, and the maximum time to excitation (tau max). The rheobase reflected the slope of the second portion. Upon varying the fibre length the slope of the first and the second linear portions and the rheobase changed. The membrane capacitance substantially affected both the value of Q0 (as in the case of myelinated fibres) and the rheobase. The accommodative processes affected the Q0, the slope of the first line, tau max, and, consequently, the rheobase. The effect of potassium activation was stronger than that of sodium inactivation. The slope of the first line, tau max, and the rheobase might be considered more comprehensive indicators of the accommodative processes than the usually used indicators.     

Surface effects in preparation of cell-size liposomes

Effects of surface type and area were shown to be important in the yield of cell-size liposomes, but not in determining their size. The liposomes were prepared by dissolving lipids in a chloroform-methanol solution and then evaporating the solvent under nitrogen in the presence of glass beads. After evaporation of the solvent, which was rapid due to the increased surface area, the dried lipids were then swollen in water at high temperatures (higher than the phase transition of the lipids), which led to formation of giant liposomes. The number of liposomes prepared in the presence of pyrex glass beads, which increase more than 100-times the surface area of lipid-glass contact, is more than 5-times larger than in the control experiments without glass beads. The yield of liposomes in the presence of another type of glass bead was almost the same as in the control experiments. These effects may be due to long- and short-range intermolecular interactions in the glass/water/lipid system.     

Haemosporidian infections in skylarks (<Emphasis Type="Italic">Alauda arvensis</Emphasis>): a comparative PCR-based and microscopy study on the parasite diversity and prevalence in southern Italy and the Netherlands

Changes in agricultural management have been identified as the most probable cause for the decline of Skylark (Alauda arvensis) populations in Europe. However, parasitic infections have not been considered as a possible factor influencing this process. Four hundred and thirty-four Skylarks from the Southern Italy and the Netherlands were screened for haemosporidian parasites (Haemosporida) using the microscopy and polymerase chain reaction (PCR)-based methods. The overall prevalence of infection was 19.5%; it was 41.8% in Italian birds and 8.3% in Dutch birds. The prevalence of Plasmodium spp. was 34.1% and 6.5% in Skylarks from Italy and Netherlands, respectively. Approximately 15% of all recorded haemosporidian infections were simultaneous infections both in Italian and Dutch populations. Six different mitochondrial cytochrome b (cyt b) lineages of Plasmodium spp. and three lineages of Haemoproteus tartakovskyi were found. The lineage SGS1 of Plasmodium relictum was the most prevalent at both study sites; it was recorded in 24.7% of birds in Italy and 5.5% in the Netherlands. The lineages SYAT05 of Plasmodium vaughani and GRW11 of P. relictum were also identified with a prevalence of <2% at both study sites. Two Plasmodium spp. lineages (SW2 and DELURB4) and three H. tartakovskyi lineages have been found only in Skylarks from Italy. Mitochondrial cyt b lineages SYAT05 are suggested for molecular identification of P. vaughani, a cosmopolitan malaria parasite of birds. This study reports the greatest overall prevalence of malaria infection in Skylarks during the last 100 years and shows that both Plasmodium and Haemoproteus spp. haemosporidian infections are expanding in Skylarks so it might contribute to a decrease of these bird populations in Europe.     

Electrofusion of fragile mutants of Saccharomyces cerevisiae

This communication presents experimental evidence that intact fragile (osmotic sensitive) yeasts can be electrofused and give viable hybrids. The yield increases with one order of magnitude for electrofusion of intact fragile yeasts with protoplasts of non-fragile ones. The yield of viable hybrids, obtained by electrofusion of protoplasts of fragile and non-fragile yeasts, is one order of magnitude higher than the yield from protoplasts of non-fragile yeasts. The destabilized cell wall and plasma membrane of the mutant yeasts could be a possible explanation for this phenomenon.     

Effect of caffeine on intrachromosomal distribution of chromatid aberrations induced by chemical mutagens in Crepis capillaris L

The intrachromosomal distribution patterns of chromatid aberrations induced by N-methyl-N-nitrosourethane (MNU), N-ethyl-N-nitrosourethane (ENU) and ethyleneimine (EI) were compared with those induced by combined treatment with the same mutagens and caffeine, the latter being considered as an inhibitor of post-replication repair of DNA.Chromatid aberrations induced by mutagens alone were distributed non-randomly along the chromosomes. In certain regions few aberrations were located; in others pronounced clustering of aberrations was observed and these regions were considered to be hot spots. This refers especially to MNU- and EI-induced aberrations, whereas ENU-induced chromatid aberrations showed a more length-proportional distribution. In ENU experiments, certain chromosomal segments also represented hot spots, but these were less pronounced. The distribution patterns of chromatid aberrations induced by combined treatment with mutagens and caffeine differed significantly from those observed in experiments with the mutagens only. There seemed to be a tendency to approach random distribution here. This was a result both of the decrease in the quantity of the aberrations in the regions, which in the experiments with mutagens only were hot spots, and of its increase in other chromosomal regions. Some of these regions were considered as hot spots but they were less pronounced. These tendencies refer to MNU and EI. Certain differences between the two variants, with the without caffeine, in ENU experiments were observed but these were of lower expressivity.The causes od differential sensivity of chromosomal regions are discussed. The conclusion is drawn that clustering of chromatid aberrations in certain chromosomal regions is due to differences in the repair systems acting in heterochromatic and euchromatic regions.     

Cryo-electron microscopy structures of the N501Y SARS-CoV-2 spike protein in complex with ACE2 and 2 potent neutralizing antibodies

The recently reported “UK variant” (B.1.1.7) of SARS-CoV-2 is thought to be more infectious than previously circulating strains as a result of several changes, including the N501Y mutation. We present a 2.9-Å resolution cryo-electron microscopy (cryo-EM) structure of the complex between the ACE2 receptor and N501Y spike protein ectodomains that shows Y501 inserted into a cavity at the binding interface near Y41 of ACE2. This additional interaction provides a structural explanation for the increased ACE2 affinity of the N501Y mutant, and likely contributes to its increased infectivity. However, this mutation does not result in large structural changes, enabling important neutralization epitopes to be retained in the spike receptor binding domain. We confirmed this through biophysical assays and by determining cryo-EM structures of spike protein ectodomains bound to 2 representative potent neutralizing antibody fragments.     

Antibacterial Activity of Vancomycin Encapsulated in Poly(DL-lactide-co-glycolide) Nanoparticles Using Electrospraying

Probiotics and Antimicrobial Proteins - Vancomycin is often used to treat infections caused by β-lactam-resistant bacteria. However, methicillin-resistant strains of Staphylococcus aureus...     

AllerTOP v.2—a server for in silico prediction of allergens

The microcosmic mechanism of the Menshutkin reaction between DABCO and benzyl fluoride/fluorodiphenylmethane has been investigated in both the gas and solvent phase by performing DFT calculations at B3LYP/6-31G(d,p) level of theory. The Gibbs free energy profiles to reach the possible transition states, i.e., five-membered ring transition state and S_N2 transition state show that the reaction between DABCO and benzyl fluoride proceeds through S_N2 transition state in accordance with previously reported studies, while the reaction between DABCO and fluorodiphenylmethane proceeds through five-membered ring transition state contrary to earlier literature. The role of solvent has been elucidated by reoptimizing the structures using SMD model of solvation. Hydrogen bonding and steric hinderance have been identified as the key factors in guiding the reaction pathway of commercially important Menshutkin reaction.