Inorganic phosphate stimulates the toxic effects of Tl+ in rat liver mitochondria

We studied action of inorganic phosphate (P(i)) on toxic effects of Tl+ in isolated rat liver mitochondria. This is a convenient model to study the toxicity of heavy metals. P(i) markedly retarded contraction of energized mitochondria swollen in the TlNO3 medium and even stronger stimulated swelling and state 4 of succinate-energized mitochondria in the TlNO3 medium. A valinomycin-induced decrease of K+-diffusion potential was also accelerated by Tl+ in the presence of P(i). The mitochondrial permeability transition pore in the medium containing Ca2+, TlNO3, and nitrates of univalent cations was distinctly stimulated by P(i). However, P(i) did not affect both the Tl+-stimulated swelling of nonenergized mitochondria in the TlNO3 medium and swelling of energized mitochondria in the Tl acetate medium. Respiration stimulated by 2,4-dinitrophenol and monoamine oxidase activity of energized mitochondria were not affected by Tl+ regardless of the presence of P(i). We suggested that stimulation by P(i) of toxic action of Tl+ in mitochondria and cells could be due to even greater enhancement of uncoupling of mitochondria as shown by an additional increase of swelling and state 4, and in the greater probability of opening of MPTP in the presence of P(i) and Ca2+.     

Hydrophobic drug delivery by self-assembling triblock copolymer-derived nanospheres

We describe the synthesis and characterization of a family of biocompatible ABA-triblock copolymers that comprised of hydrophilic A-blocks of poly(ethylene glycol) and hydrophobic B-blocks of oligomers of suberic acid and desaminotyrosyl-tyrosine esters. The triblock copolymers spontaneously self-assemble in aqueous solution into nanospheres, with hydrodynamic diameters between 40 and 70 nm, that do not dissociate under chromatographic and ultracentrifugation conditions. These nanospheres form strong complexes with hydrophobic molecules, including the fluorescent dye 5-dodecanoylaminofluorescein (DAF) and the antitumor drug, paclitaxel, but not with hydrophilic molecules such as fluorescein and Oregon Green. The nanosphere-paclitaxel complexes retain in vitro the high antiproliferative activity of paclitaxel, demonstrating that these nanospheres may be useful for delivery of the hydrophobic drugs.     

Nutritional and chlorophyll fluorescence responses of lucerne (<Emphasis Type="Italic">Medicago sativa</Emphasis>) to waterlogging and subsequent recovery

Periodic flooding of perennial crops such as lucerne (Medicago sativa,L) is a major cause of lowered productivity and leads in extreme cases to plant death. In this study, effects of waterlogging and subsequent recovery on plant nutrient composition and PSII photochemistry were studied to gain a better understanding of the mechanisms of recovery as they relate to leaf photochemistry (chlorophyll fluorescence) and nutrient dynamics. Three lucerne cultivars and one breeding line were flooded for 20 d, drained and left to recover for another 16 d under glasshouse conditions. Leaf and root nutrient composition (P, K, Ca, Mg, B, Cu and Zn) of waterlogged lucerne was significantly lower than in freely drained controls, leaf N concentrations were also significantly lower in waterlogged lucerne. At the same time, there were significantly (5-fold) higher concentrations of Fe in waterlogged roots and Na in leaves (2-fold) of stressed plants. PS II photochemistry, which was impaired due to waterlogging, recovered almost fully after 16 d of free drainage in all genotypes. Alongside fluorescence recovery, concentrations of several nutrients also increased in recovered plants. Growth parameters, however, remained suppressed after draining. The latter was due to both the smaller capacity of CO₂ assimilation in previously waterlogged plants (caused in part by nutrient deficiency and associated inhibition of PSII) and the plants need to re-direct available nutrient and assimilate pools to repair the damage to the photosynthetic apparatus and roots. It is concluded, that for any lucerne-breeding program it is important to determine not only the degree of tolerance to waterlogging but also the potential for recovery of different genotypes, as well as look for outstanding individuals within each population.     

HIM1, a new yeast Saccharomyces cerevisiae gene playing a role in control of spontaneous and induced mutagenesis

We have identified a new Saccharomyces cerevisiae gene, HIM1, mapped on the right arm of the chromosome IV (ORF YDR317w), mutations in which led to an increase in spontaneous mutation rate and elevated the frequencies of mutations, induced by UV-light, nitrous acid, ethylmethane sulfonate and methylmethane sulfonate. At the same time, him1 mutation did not result in the increase of the sensitivity to the lethal action of these DNA-damaging agents. We tested the induced mutagenesis in double mutants carrying him1 mutation and mutations in other repair genes: apn1, blocking base excision repair; rad2, rev3, and rad54, blocking three principal DNA repair pathways; pms1, blocking mismatch repair; hsm2 and hsm3 mutations, which lead to a mutator effect. Epistatic analysis showed a synergistic interaction of him1 with pms1, apn1, and rad2 mutations, and epistasis with the rev3, the rad54, the hsm2, and the hsm3. To elucidate the role of the HIM1 in control of spontaneous mutagenesis, we checked the repair of DNA mispaired bases in the him1 mutant and discovered that it was not altered in comparison to the wild-type strain. In our opinion, our results suggest that HIM1 gene participates in the control of processing of mutational intermediates appearing during error-prone bypass of DNA damage.     

Assignment of the αB-crystallin gene to human chromosome 11

Using a human αB-crystallin genomic probe and human-mouse somatic cell hybrids, the human αB-gene was assigned to chromosome 11 and further corroborated by in situ hybridization to normal metaphase chromosomes. This assignment confirmed and regionally mapped the locus to q22.3–23.1.     

Oribatid mites (Acari,Oribatida) from riverine environments of some islands in Oceania

A checklist of identified oribatid mite taxa from riverine freshwater environments from six islands in Polynesia (New Caledonia, Tahiti, Moorea, Rurutu, Tubuai, Raiatea) is presented; 18 species, 16 genera and eight families were recorded. Trhypochthoniellus longisetus (Berlese, 1904) and Trimalaconothrus albulus Hammer, 1972 prevailed on distribution. Fortuynia smitisp. n. (Fortuyniidae) is described from New Caledonia. The new speciesis morphologically most similar to Fortuynia marina Hammen, 1960 from New Guinea, but it differs from the latter by the longer notogastral setae dm, lm, c₂, p₁, epimeral setae 3b and adanal setae ad₁ and the presence of prodorsal lateral ridges.     

SSB functions as a sliding platform that migrates on DNA via reptation

SSB proteins bind to and control the accessibility of single-stranded DNA (ssDNA), likely facilitated by their ability to diffuse on ssDNA. Using a hybrid single-molecule method combining fluorescence and force, we probed how proteins with large binding site sizes can migrate rapidly on DNA and how protein-protein interactions and tension may modulate the motion. We observed force-induced progressive unraveling of ssDNA from the SSB surface between 1 and 6 pN, followed by SSB dissociation at ～10 pN, and obtained experimental evidence of a reptation mechanism for protein movement along DNA wherein a protein slides via DNA bulge formation and propagation. SSB diffusion persists even when bound with RecO and at forces under which the fully wrapped state is perturbed, suggesting that even in crowded cellular conditions SSB can act as a sliding platform to recruit and carry its interacting proteins for use in DNA replication, recombination and repair.     

Inhibition of Microsomal Lipid Peroxidation and Cytochrome P-450-Catalyzed Reactions by Nitrofuran Compounds

(5-Nitro-2-furfuryliden)amino compounds bearing triazol-4-yl, benzimidazol-l-yl, pyrazol-l-yl, triazin-4-yl or related groups (a) stimulated superoxide anion radical generated by rat liver microsomes in the presence of NADPH and oxygen; (b) inhibited the NADPH-dependent, iron-catalyzed microsomal lipid peroxidation; (c) prevented the NADPH-dependent destruction of cytochrome P-450; (d) inhibited the NADPH-dependent microsomal aniline 4-hydroxylase activity; (e) failed to inhibit either the cumenyl hydroperoxide-dependent lipid peroxidation or the aniline-4-hydroxylase activity, except for the benzimidazol-l-yl and the substituted triazol-4-yl derivatives, which produced minor inhibitions. Reducing equivalents enhanced the benzimidazol-l-yl derivative inhibition of the cumenyl hydroperoxide-induced lipid peroxidation. The ESR spectrum of the benzimidazol-l-yl derivative, reduced anaerobically by NADPH-supplemented microsomes, showed characteristic spin couplings. Compounds bearing unsaturated nitrogen heterocycles were always more active than those bearing other groups, such as nifurtimox or nitrofurazone. The energy level of the lowest unoccupied molecular orbital was in fair agreement with the capability of nitrofurans for redox-cycling and related actions. It is concluded that nitrofuran inhibition of microsomal lipid peroxidation and cytochrome P-450-catalyzed reactions was mostly due to diversion of reducing equivalents from NADPH to dioxygen. Trapping of free radicals involved in propagating lipid peroxidation might contribute to the overall effect of the benzimidazol-l-yl and substituted triazol-4-yl derivitives.