高碘酸钠氧化法测定肌醇含量

高碘酸钠氧化法测定肌醇含量张楚富，林清华，梁会（武汉大学生命科学学院武汉４３００７２）王泽胜（湖南兰龙科技实业公司长沙４１０００６）关键词植酸钙，肌醇，高碘酸钠氧化法分类号Ｑ５０８肌醇是一种环己六醇，它以植酸盐的形式主要存在于米糠和其他油料作物种子中...     

Oxidation of guanines in the iron-responsive element RNA: similar structures from chemical modification and recent NMR studies

Background: The translation or stability of the mRNAs from ferritin, m-aconitase, erythroid aminoevulinate synthase and the transferrin receptor is controlled by the binding of two iron regulatory proteins to a family of hairpin-forming RNA sequences called iron-responsive elements (IREs). The determination of higher-solution nuclear magnetic resonance (NMR) structures of IRE variants suggests an unusual hexaloop structure, leading to an intra-loop G-C base pair and a highly exposed loop guanine, and a special internal loop/bulge in the ferritin IRE involving a shift in base pairing not predicted with standard algorithms.Results: Cleavage of synthetic 55- and 30-mer RNA oligonucleotides corresponding to the ferritin IRE with complexes based on oxoruthenium(IV) shows enhanced reactivity at a hexaloop guanine and at a guanine adjacent to the internal loop/bulge with strong protection at a guanine in the internal loop/bulge. These results are consistent with the recent NMR structures. The synthetic 55-mer RNA binds the iron-regulatory protein from rabbit reticulocyte lysates. The DNA analogs of the 55- and 30-mers do not show the same reactivity pattern.Conclusions: The chemical reactivity of the guanines in the ferritin IRE towards oxoruthenium(IV) supports the published NMR structures and the known oxidation chemistry of the metal complexes, The results constitute progress towards developing stand-alone chemical nucleases that reveal significant structural properties and provide results that can ultimately be used to constrain molecular modeling.     

Air-exposure effect on the resistivity of thin bismuth films

A survey of previous studies on vacuum deposited metal films shows that in high frequency measurements, explicit reference to the effect of air-exposure is not made. The present work on bismuth films (in-situ and air-exposed) at dc and rf frequencies, carried out mainly to study the air-exposure effect, shows that in-situ dc and rf and exposed rf all show nearly the same resistivity for thick continuous films. But air-exposed dc film resistances, when compared to in-situ dc resistances, show that the grain boundary reflection coefficient, R _gin Mayadas-Shatzkes model changes from 0·2 to 0·6. This is shown to be due to the grain boundary oxidation. The result is substantiated by rf measurements.