Binding properties of HABA-type azo derivatives to avidin and avidin-related protein 4

The chicken genome encodes several biotin-binding proteins, including avidin and avidin-related protein 4 (AVR4). In addition to D-biotin, avidin binds an azo dye compound, 4-hydroxyazobenzene-2-carboxylic acid (HABA), but the HABA-binding properties of AVR4 are not yet known. Differential scanning calorimetry, UV/visible spectroscopy, and molecular modeling were used to analyze the binding of 15 azo molecules to avidin and AVR4. Significant differences are seen in azo compound preferences for the two proteins, emphasizing the importance of the loop between strands beta3 and beta4 for azo ligand recognition; information on these loops is provided by the high-resolution (1.5 A) X-ray structure for avidin reported here. These results may be valuable in designing improved tools for avidin-based life science and nanobiotechnology applications.     

Tantal und Niob

Ohne Zusammenfassung     

Die Verwendung des Cupferrons in der quantitativen Analyse

Ohne Zusammenfassung Die Zitate zu diesem Referat folgen ausnahmsweise am Schlusse des ganzen Artikels S. 66.     

The Effects of a Strong Disaggregating Agent on Sec-Page of Aquatic and Soil Humic Matter

Abstract

Size-exclusion chromatographic (SEC) fractionation and electrophoretic separation of aquatic humic matter samples from a Finnish lake using Sephadex G-75 with 7 M urea solution as eluent and 10% polyacrylamide gel (PAGE) with urea and sodium dodecyl sulphate solution (SDS), respectively, were performed and compared to similar analyses performed on a Russian chernozem soil humic acid sample and Nordic reference fulvic and humic acid samples. The integrated whole of aquatic humic solutes and soil humic acids were found to exhibit similar SEC-PAGE behaviours. Humic matter was not excessively disaggregated by the 7 M urea and hence SEC-PAGE can with confidence be applied as a coarse, initial fractionation procedure or for certain predeterminations of the structural composition.     

Precision of Isolation of Aquatic Humic Matter by Xad-Resin Technology from NMR Spectroscopy's Point of View

Abstract

The most crucial question in the aquatic humus chemistry is a reliable and selective separation and fractionation of the humic solutes from other organic and inorganic constituents. The dilute solutions of natural dissolved organic matter must in a way or another be concentrated before fractionation and molecular characterization. The most popular method for this purpose is the application of non-ionic macroporous resins at preadjusted acidity. The routine is fractionate further at strongly acidic conditions the obtained mixture of hydrophobic humic solutes into so-called humic and fulvic acids. Quantitatively and in the light of elemental analysis and basic functional groups this fractionation seems to be reliable. However, from the point of view of the structural composition, the precision of the procedure was not so self-evident. The data of nuclear magnetic resonance spectroscopy has proved that it is slightly erratic to repeat from the standard homogeneous water sample the isolation-fractionation for obtaining structurally wholly identical humic and fulvic acids. This deviation was not solely as a result of the technique itself, but also of the highly sensitive nature of the humic solutes.     

Binary tree approach to scaling in unimodal maps

Ge, Rusjan, and Zweifel introduced a binary tree which represents all the periodic windows in the chaotic regime of iterated one-dimensional unimodal maps. We consider the scaling behavior in a modified tree which takes into account the self-similarity of the window structure. A nonuniversal geometric convergence of the associated superstable parameter values towards a Misiurewicz point is observed for almost all binary sequences with periodic tails. For these sequences the window period grows arithmetically down the binary tree. There are an infinite number of exceptional sequences, however, for which the growth of the window period is faster. Numerical studies with a quadratic maximum suggest more rapid than geometric scaling of the superstable parameter values for such sequences.