Xylan biosynthesis

The effect of the base used for the condensation of xylose (7) with pentane-2,4-dione (1) was carefully examined. The best results were obtained using NaOH since 54 was obtained in 45 min at 50°C in 97% yield. Reduction of 54 gave 60, an activator of glycosaminoglycans biosynthesis, launched on the market in cosmetic skincare products as Pro-Xylane by L Oreal in 2006 [116, 117] (Fig. 10). 

Fig. 10 Structure of Pro-Xylane , an activator of glycosaminoglycans biosynthesis (L Oreal)...

Saraswat, V and Bisaria, V S., Biosynthesis of xylanolytic and xylan-debranching enzymes in Melanocarpus albomyces IIS 68. J Fermentation Bioeng 1997, 83 (4), 352-357. 

In Volume 33 of this Series, we presented1 a review of the crystalline structures of polysaccharides published during the period 1967-1974. Detailed accounts of progress in structural studies on specific types of polysaccharides were presented in the Proceedings of the Twenty-sixth Symposium of the Colston Research Society and were subsequently published as a book.2 Precise methods for X-ray diffraction analysis of biopolymer structures were discussed by Hukins.3 The aspects of the structures of cellulose, mannan, and xylan, their organization in the cell wall, and the biosynthesis of cell-wall polysaccharides were described by Mackie.4 Work on the structures of the connective-tissue polysaccharides, O-acetylcellulose, and the various forms of amylose was reviewed by Atkins,5 Chanzy,6 and Sarko,7... 

Hemicelluloses are synthesized by glycosyltransferases located in the Golgi membranes. Many glycosyltransferases needed for the biosynthesis of xyloglucans and mannans are known. In contrast, the biosynthesis of xylans and j8-[1 3,1 4]-glucans remains very elusive [15]. 

A caveat must be made at this point. This model is hypothetical, but it is the simplest that is consistent with the one linkage-one enzyme hypothesis and with the chemical evidence for the structures of xylans. Any further structural elaboration in the xylans must be primarily in their patterns of branching and that implies yet further intricacy in the biosynthesis of these branches. Interpretations other than those assumed here can be placed upon the data obtained by the partial degradation of xylans, but they do not alter one basic conclusion the side-chains of xylans are usually more complex in terms of biosynthesis than are the main core sequences. This suggests that the xylans may be examples of molecules in which encoded information of some sort is held in a three-dimensional array upon a non-informational substructure. In this case the helical core will support a somewhat brush-like array of side chains. Any information contained in the specific side chains probably relates to the construction and organisation of the cell wall, but in what way is unknown. 

Bacterial cellulose (BC) is frequently studied in order to clarify the mechanism for biosynthesis of cellulose (Tokoh et al. 2002a). Details of mechanisms for biopolymerization and simultaneous crystallization in long parallel rows of extended chains are understood fairly well. As an example of the nature of such studies, effects of pectin and xylan medium on the crystallite morphology have been demonstrated (Tokoh et al. 2002b). 

These results show the interest of our approach based upon biomimicry and green chemistry to select a new active ingredient of high performance in skin anti-ageing strategy. Compound 18 selected as the best activator of the biosynthesis of GAGs in vitro, was further confirmed also very active in vivo in a clinical trial when topically applied. Introduced in cosmetic skin care products,it has been marketed under the trade name Pro-Xylane . 

The gibberellic acid-induced biosynthesis and release of cell-wall degrading e/jrfo-D-xylanase by isolated aleurone layers of barley have been studied. Studies on the D-xylanase system of Streptomyces species have included a study of the action of the enzyme on various o-xylans and D-xylo-oligosaccharides. The isolation and structural identification of arabino-D-xylo-oligosaccharides arising from action of the enzyme on corn cob arabino-D-xylan were reported. Mutant strains of Trichoderma viride not producing D-xylanase have been induced and isolated with the aid of nystatin selection. ... 

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