Structural characteristics of arabinoxylans from barley, malt and wort = Structuurkenmerken van arabinoxylanen uit gerst, mout en wort

Flours from dehusked barley and malt were fractionated to obtain water-insoluble cell wall material (WIS). A mass balance of these fractionations was determined. Arabinoxylans were extracted from this WIS in high purity and yield with Ba(OH) 2 , and subfractionated with graded ethanol precipitation.The structural elements present in these arabinoxylans and in arabinoxylans isolated from wort were determined. These arabinoxylans all consisted of a backbone of (1-->4)-linked β-D-xylopyranose units (Xyl p ), a proportion of which were substituted with alfa-L- arabinofuranose (Ara f ) at O-2 and/or O-3 of the Xyl p units. A new feature was the presence in barley and malt arabinoxylans of a large amount of Xyl p units carrying a single Ara f substituent at O-2. The amounts of Xyl p substituted at O-2 or at both O-2 and O-3 increased with increasing substitution of the xylan backbone. The wort arabinoxylans were found to be exceptionally rich in O-2,3-disubstituted Xyl p .A number of fragments could be isolated after degradation of barley and malt arabinoxylans with endoxylanase 1 from Aspergillus awamori . The structures of the isolated fragments were determined. From the structures found, it could be shown that the position of Ara f substituents on the xylose residues of the arabinoxylan influenced the extent of enzymic degradation of the xylan backbone, substituents at O-2 being more efficient than substituents at O-3 with the enzyme used. From these data and the linkage composition of undegradable arabinoxylan fractions, it was concluded that the distribution of Ara f substituents over the xylan chain was not random, but fairly regular.The arabinoxylans extracted from barley and malt cell wall material appeared to be very similar in composition and structural features. This implies that changes during malting are small or extremely localized

A priori crystal structure prediction of native cellulose

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Unravelling cell wall formation in the woody dicot stem

Populus is presented as a model system for the study of wood formation (xylogenesis). The formation of wood (secondary xylem) is an ordered developmental process involving cell division, cell expansion, secondary wall deposition, lignification and programmed cell death. Because wood is formed in a variable environment and subject to developmental control, xylem cells are produced that differ in size, shape, cell wall structure, texture and composition. Hormones mediate some of the variability observed and control the process of xylogenesis. High-resolution analysis of auxin distribution across cambial region tissues, combined with the analysis of transgenic plants with modified auxin distribution, suggests that auxin provides positional information for the exit of cells from the meristem and probably also for the duration of cell expansion. Poplar sequencing projects have provided access to genes involved in cell wall formation. Genes involved in the biosynthesis of the carbohydrate skeleton of the cell wall are briefly reviewed. Most progress has been made in characterizing pectin methyl esterases that modify pectins in the cambial region. Specific expression patterns have also been found for expansins, xyloglucan endotransglycosylases and cellulose synthases, pointing to their role in wood cell wall formation and modification. Finally, by studying transgenic plants modified in various steps of the monolignol biosynthetic pathway and by localizing the expression of various enzymes, new insight into the lignin biosynthesis in planta has been gained.Journal ArticleResearch Support, Non-U.S. Gov'tReviewinfo:eu-repo/semantics/publishe

The C/EBP family of transcription factors in the liver and other organs

Members of the CCAAT/enhancer-binding protein (C/EBP) family of transcription factors are pivotal regulators of liver functions such as nutrient metabolism and its control by hormones, acute-phase response and liver regeneration. Recent progress in clarification of regulatory mechanisms for the C/EBP family members gives insight into understanding the liver functions at the molecular level