Application of an EF following irradiation greatly increases cell death. The observation that the DNA repair shoulder in the survival curve of C. albicans is suppressed when cells are exposed to irradiation + EF suggests that EF likely inactivate cellular recovering processes. The result for the number of nuclei with gamma-H2AX foci in MRC5 cells indicates that an EF interferes mostly in the DNA repair mechanisms. A molecular ad-hoc model is proposed.
The accumulation and microdistribution of uranium in the bone and marrow of Beagle dogs were determined by both neutron activation and neutron-fission analysis. The experiment started immediately after the weaning period, lasting till maturity. Two animal groups were fed daily with uranyl nitrate at concentrations of 20 and 100 microg g(-1) food. Of the two measuring techniques, uranium accumulated along the marrow as much as in the bone, contrary to the results obtained with single, acute doses. The role played by this finding for the evaluation of radiobiological long-term risks is discussed. It was demonstrated, by means of a biokinetical approach, that the long-term accumulation of uranium in bone and marrow could be described by a piling up of single dose daily incorporation.
The effects of nucleon effective mass on the Pauli-blocking function are worked out. We have shown that such effects on the quasi-deuteron mechanism of photonuclear absorption are rather relevant. The Pauli-blocking function has been evaluated by applying a Monte Carlo calculation particularly suitable for simulation of intranuclear cascade processes of intermediate-energy nuclear reactions. The nucleon binding in the photonuclear absorption mechanism is taken into account accordingly.
Previously, we proposed a novel mechanism of antibacterial translocation through the general diffusion porin OmpC in Gram-negative E. coli (Abstract 12-A-3857-BPS, 2668-Pos). Our proposed mechanism explains the observed rapid translocation of substrates capable of replacing the H-bonds of solvating water in the channel constriction zone upon evacuation of this water to bulk solvent. This hypothesis is based on previous work linking protein-ligand association and dissociation barriers in general to the costs of water transfer to/from binding sites. In the current study, we investigated a set of 8 carbapenems (including known drugs and antibacterials in development) for their structure-translocation kinetic relationships with OmpC using electrophysiology and microbiology methods. Taking into account the supporting electrophysiology and microbiology data, we demonstrated that these molecules likewise translocate through OmpC porin at rates that depend on their polar composition and H-bond replacement ability. The additional acidic group of ertapenem compared to other analogs promoted the highest entry rate into OmpC (kon~2x104 M-1s-1). Zwitterionic compounds with highly polar groups attached to the penem-2 ring (i.e. panipenem, imipenem and doripenem) exhibited faster kon (>104 M-1s-1), while those zwitterionic analogs with fewer exposed polar groups (i.e. meropenem and biapenem) exhibited slower kon (~5x103 M-1s-1). Tebipenem pivoxil, a pro-dug developed for oral absorption, and razupenem with a change to thiazol-2-yl-thio moiety exhibited the slowest kon rates in to OmpC (~1.5x103 M-1s-1) and also showed interaction with the phospholipid membrane. Our findings may help better understand the molecular mechanisms underlying antibiotic uptake through the outer membrane of Gram-negative bacteria, which is a key step in achieving antibiotic exposure and efficacy at intracellular targets.
A model based on Watson's power law for the species-area relationship predicts that full global warming, projected up to the year 2050, could provoke the disappearance of roughly one-quarter of existing species. Here, an alternative approach is worked out, based on the combination of two ecology laws: Taylor and Watson's power laws, where the former relates species variability with their mean abundance. Just how severely global warming would affect not only the number but the diversity of the surviving species is addressed by this approach, while at the same time giving indications for the post-disaster fate of the remaining species (extinction or recovery).
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