Biomedical subjects
Publications and source records attributed to R Ji.
(S)-(-)-ofloxacin is one of the best fluoroquinolone agents in current clinical use. A new facile practical route with good yield and high optical purity to stereospecific synthesis of (S)-(-)-ofloxacin was described.
The mechanism of inhibition of peptidyl inhibitors with thrombin was studied using molecular modeling, molecular mechanics, and CoMFA statistical analysis. A new procedure for the elucidation of binding conformations, BCSPL, is described and was employed to obtain the binding conformers of a series of 18 tripeptidyl thrombin inhibitors. Energetic studies and QSAR analysis of the BCSPL-derived conformers indicated a modest correlation between the calculated binding energies of the title compounds and their inhibitory activities to human alpha-thrombin. CoMFA analysis of the BCSPL alignment resulted in a satisfactory model of the thrombin active site.
The homogenized tissue samples of puffer fish were extracted with boiling 0.1% acetic acid solution for 2 times, then the combined filtrate was defatted with ether ethyl for 2 times and the water phase were diluted with 0.05 mol/L PBS for ELISA determination (adjusted pH to 6.5-7.0). The results showed that the minimum detecable concentration of tetrodotoxin was 1.0 x 10(-3) mg/L (0.1 ng/assay), and the standard curve was linear between 1.0 x 10(-2) and 1.0 mg/L. The recovery rates from tetrodotoxin spiked samples of this method were 73.8%-117.4%. The accuracy of ELISA was compared with the traditional mouse bioassay system. The results showed no significant differences between the two methods (for paired-t test, P > 0.2), and significant correlations in tetrodotoxin concentration were obtained (r = 0.916).
Akr1p, which contains six ankyrin repeats, was identified during a screen for mutations that displayed synthetic lethality with a mutant allele of the bud emergence gene BEM1. Cells from which AKR1 had been deleted were alive but misshapen at 30 degrees C and inviable at 37 degrees C. During a screen for mutants that required one or more copies of wild-type AKR1 for survival at 30 degrees C, we isolated mutations in GPA1, which encodes the G alpha subunit of the pheromone receptor-coupled G protein. (The active subunit of this G protein is G beta gamma, and G alpha plays an inhibitory role in G beta gamma-mediated signal transduction.) AKR1 could serve as a multicopy suppressor of the lethality caused by either loss of GPA1 or overexpression of STE4, which encodes the G beta subunit of this G protein, suggesting that pheromone signaling is inhibited by overexpression of Akr1p. Mutations in AKR1 displayed synthetic lethality with a weak allele of GPA1 and led to increased expression of the pheromone-inducible gene FUS1, suggesting that Akr1p normally (and not just when overexpressed) inhibits signaling. In contrast, deletion of BEM1 resulted in decreased expression of FUS1, suggesting that Bem1p normally facilitates pheromone signaling. During a screen for proteins that displayed two-hybrid interactions with Akr1p, we identified Ste4p, raising the possibility that an interaction between Akr1p and Ste4p contributes to proper regulation of the pheromone response pathway.
The survey of T-2 toxin in wheat randomly sampled in nine provinces was carried out, employing an indirect competitive enzyme-linked immunosorbent assay. Among 330 samples, 264 samples (80%) showed positive results. The mean concentrations was 53.3 ppb. and maximal concentration was 1122.0 ppb. It was also detected high concentration (84.5-1064.4) of T-2 toxin in human intoxication wheat samples in 1991. The investigation also showed that there existed close relationship between the level of T-2 toxin contamination and the epidemic of wheat scabby.
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