Interactions of Phenolic Acids and β-Glucan: Studies of Adsorption Isotherms and Thermodynamics

Interactions between polyphenols and dietary fiber might play an important role in polyphenol bioactivities. These interactions can be studied through adsorption processes. The aim of this study was to investigate the adsorption of phenolic acids (p-coumaric acid, caffeic acid, chlorogenic acid) onto dietary fiber – β-glucan. Adsorption was carried out at different temperatures (25, 37, and 45 °C) and pH values (1.5, 5.5, and 10). Non-linear isotherm adsorption models (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin, Hill) were applied to analyze the data. Experimentally determined adsorption capacities showed some fluctuations with temperature and pH. Adsorption isotherms modelled the experimentally determined adsorption capacities well. According to isotherm parameters, it can be suggested that the adsorption was a physical process with non-covalent bonding at all temperatures and pH. Thermodynamic parameters showed that the adsorption was spontaneous (except for chlorogenic acid) and exothermic. Adsorption isotherms and thermodynamics gave useful information about phenolic acid – β-glucan interactions. This work is licensed under a Creative Commons Attribution 4.0 International License

Gene duplication, modularity and adaptation in the evolution of the aflatoxin gene cluster

<p>Abstract</p> <p>Background</p> <p>The biosynthesis of aflatoxin (AF) involves over 20 enzymatic reactions in a complex polyketide pathway that converts acetate and malonate to the intermediates sterigmatocystin (ST) and <it>O</it>-methylsterigmatocystin (OMST), the respective penultimate and ultimate precursors of AF. Although these precursors are chemically and structurally very similar, their accumulation differs at the species level for Aspergilli. Notable examples are <it>A</it>. <it>nidulans </it>that synthesizes only ST, <it>A</it>. <it>flavus </it>that makes predominantly AF, and <it>A</it>. <it>parasiticus </it>that generally produces either AF or OMST. Whether these differences are important in the evolutionary/ecological processes of species adaptation and diversification is unknown. Equally unknown are the specific genomic mechanisms responsible for ordering and clustering of genes in the AF pathway of <it>Aspergillus</it>.</p> <p>Results</p> <p>To elucidate the mechanisms that have driven formation of these clusters, we performed systematic searches of aflatoxin cluster homologs across five <it>Aspergillus </it>genomes. We found a high level of gene duplication and identified seven modules consisting of highly correlated gene pairs (<it>aflA/aflB, aflR/aflS, aflX/aflY</it>, <it>aflF/aflE, aflT/aflQ</it>, <it>aflC/aflW</it>, and <it>aflG/aflL</it>). With the exception of <it>A. nomius</it>, contrasts of mean <it>Ka/Ks </it>values across all cluster genes showed significant differences in selective pressure between section <it>Flavi </it>and non-section <it>Flavi </it>species. <it>A. nomius </it>mean <it>Ka/Ks </it>values were more similar to partial clusters in <it>A. fumigatus </it>and <it>A. terreus</it>. Overall, mean <it>Ka/Ks </it>values were significantly higher for section <it>Flavi </it>than for non-section <it>Flavi </it>species.</p> <p>Conclusion</p> <p>Our results implicate several genomic mechanisms in the evolution of ST, OMST and AF cluster genes. Gene modules may arise from duplications of a single gene, whereby the function of the pre-duplication gene is retained in the copy (<it>aflF</it>/<it>aflE</it>) or the copies may partition the ancestral function (<it>aflA/aflB</it>). In some gene modules, the duplicated copy may simply augment/supplement a specific pathway function (<it>aflR/aflS </it>and <it>aflX/aflY</it>) or the duplicated copy may evolve a completely new function (<it>aflT/aflQ </it>and <it>aflC/aflW</it>). Gene modules that are contiguous in one species and noncontiguous in others point to possible rearrangements of cluster genes in the evolution of these species. Significantly higher mean <it>Ka/Ks </it>values in section <it>Flavi </it>compared to non-section <it>Flavi </it>species indicate increased positive selection acting in the evolution of genes in OMST and AF gene clusters.</p

Scalar brane backgrounds in higher order curvature gravity

We investigate maximally symmetric brane world solutions with a scalar field. Five-dimensional bulk gravity is described by a general lagrangian which yields field equations containing no higher than second order derivatives. This includes the Gauss-Bonnet combination for the graviton. Stability and gravitational properties of such solutions are considered, and we particularily emphasise the modifications induced by the higher order terms. In particular it is shown that higher curvature corrections to Einstein theory can give rise to instabilities in brane world solutions. A method for analytically obtaining the general solution for such actions is outlined. Genericaly, the requirement of a finite volume element together with the absence of a naked singularity in the bulk imposes fine-tuning of the brane tension. A model with a moduli scalar field is analysed in detail and we address questions of instability and non-singular self-tuning solutions. In particular, we discuss a case with a normalisable zero mode but infinite volume element.Comment: published versio