Nucleophilic substitution reactions of pyranose polytosylates

The 2,3,4-tri-toluenesulfonate ester derivatives of the methyl pyranosides of L-arabinose, D-ribose, D-lyxose, and D-xylose have been prepared, and their substitution reactions with various nucleophiles have been examined. For arabinose, xylose, and ribose, highly regioselective monosubstitutions were observed with benzoate, nitrite, and azide anions. These reactions have led to short and simple routes from D-xylose to L-arabinose derivatives, from L-arabinose to D-xylose derivatives, and from D-ribose to L-lyxose derivatives. The tritosylate derived from methyl alpha-D-lyxopyranoside was unreactive toward nucleophilic substitution reactions, giving instead a dihydropyran product arising from an initial E2 elimination reaction of the 2-tosylate.

Wurst: a protein threading server with a structural scoring function, sequence profiles and optimized substitution matrices

Wurst is a protein threading program with an emphasis on high quality sequence to structure alignments (http://www.zbh.uni-hamburg.de/wurst). Submitted sequences are aligned to each of about 3000 templates with a conventional dynamic programming algorithm, but using a score function with sophisticated structure and sequence terms. The structure terms are a log-odds probability of sequence to structure fragment compatibility, obtained from a Bayesian classification procedure. A simplex optimization was used to optimize the sequence-based terms for the goal of alignment and model quality and to balance the sequence and structural contributions against each other. Both sequence and structural terms operate with sequence profiles.

Chromosomal genotoxicity of nitrobenzene and benzonitrile

In order to investigate the chromosomal genotoxicity of nitrobenzene and benzonitrile, we studied the induction of micronuclei (MN) by these test compounds in V79 cells, as well as effects on the formation and stability of microtubules and on motor protein functions. No cytotoxicity was seen in V79 cell cultures in terms of Neutral red uptake after 18 h treatment with up to 1 mM nitrobenzene or 1 mM benzonitrile. Subsequently, a concentration range up to 100 muM was used in the experiments on induction of MN. Both test compounds exhibit a weak, but definitely positive test result compared to the solvent (DMSO) control. Minimal effect concentrations of nitrobenzene and benzonitrile appeared as low as 0.01 muM, and no-effect-concentrations were between 0.001 and 0.005 muM. Clearly enhanced MN rates were found at 0.1 muM and higher. Both, nitrobenzene and benzonitrile, induced mostly kinetochor (CREST)-positive micronuclei, thus characterising the chromosomal effects as aneugenic. In cell-free assays, a slight effect on tubulin assembly was observed at 1 mM nitrobenzene without addition of DMSO. Higher concentrations (5 mM) led to secondary effects. In presence of 1% DMSO, nitrobenzene exerted no detectable effect on tubulin assembly up to the solubility limit in water of about 15 mM. For benzonitrile in presence of DMSO, a clear dose-response of inhibition of tubulin assembly at 37degreesC was seen above the no-effect-concentration of 2 mM, with an IC50 of 13 mM and protein denaturation starting above a level of about 20 mM. The nature of the effects of nitrobenzene and benzonitrile on the association of tubulin to form microtubules was confirmed by electron microscopy. Treatment by either 5 mM nitrobenzene or 13 mM benzonitrile plus 1% DMSO left the microtubular structure intact whereas 5 mM nitrobenzene, in absence of DMSO, led to irregular cluster formations. The experiments demonstrate that both nitrobenzene and benzonitrile, in millimolar concentration ranges, may lead to interference with tubulin assembly in a cell-free system. The functionality of the tubulin-kinesin motor protein system was assessed using the microtubule gliding assay. Nitrobenzene affected the gliding velocity in a concentration-dependent manner, starting at about 7.5 muM and reaching complete inhibition of motility at 30 muM, whereas benzonitrile up to 200 muM did not affect the kinesin-driven gliding velocity. The micronucleus assay data demonstrate a chromosomal endpoint of genotoxicity of nitrobenzene and benzonitrile. Aneugenic effects of both compounds occur at remarkably low concentrations, with lowest-effect-concentrations being 0.1 muM. This points to the relevance of interactions with the cellular spindle apparatus.

Relationships among the three major lineages of the Acari (Arthropoda : Arachnida) inferred from small subunit rRNA: Paraphyly of the parasitiformes with respect to the opilioacariformes and relative rates of nucleotide substitution

We inferred phylogeny among the three major lineages of the Acari ( mites) from the small subunit rRNA gene. Our phylogeny indicates that the Opilioacariformes is the sister-group to the Ixodida+Holothyrida, not the Ixodida+Mesostigmata+Holothyrida, as previously thought. Support for this relationship increased when sites with the highest rates of nucleotide substitution, and thus the greatest potential for saturation with nucleotide substitutions, were removed. Indeed, the increase in support ( and resolution) was despite a 70% reduction in the number of parsimony-informative sites from 408 to 115. This shows that rather than 'noisy' sites having no impact on resolution of deep branches, 'noisy' sites have the potential to obscure phylogenetic relationships. The arrangement, Ixodida+Holothyrida+Opilioacariformes, however, may be an artefact of long-branch attraction since relative-rate tests showed that the Mesostigmata have significantly faster rates of nucleotide substitution than other parasitiform mites. Thus, the fast rates of nucleotide substitution of the Mesostigmata might have caused the Mesostigmata to be attracted to the outgroup in our trees. We tested the hypothesis that the high rate of nucleotide substitution in some mites was related to their short generation times. The Acari species that have high nucleotide substitution rates usually have short generation times; these mites also tend to be more active and thus have higher metabolic rates than other mites. Therefore, more than one factor may affect the rate of nucleotide substitution in these mites.

Task substitution: where to from here?

Meeting future health workforce needs is a challenge for all health professionals.