Larch, galactans from

The first structural study of the arabinogalactan or e-galactan from European larch was carried out by Campbell, Hirst, and Jones,126 who showed the polysaccharide to contain residues of D-galactose and L-arabinose in the proportion of 6 1. Fractionation of the methylated polysaccharide gave, as the main component, a methylated galactan containing... 

Arabo-galactan from larch wood Sedimentation and Diffusion 16,000 A highly branched molecule 62... 

Further knowledge of the detailed structure of European-larch e-galactan has come from later investigations.126 127 In these studies, however, no evidence could be found for heterogeneity of the type previously encountered in the methylated derivative, and the e-galactan itself was ultracentrifugally homogeneous. 

Mild, acid hydrolysis of European-larch arabinogalactan results in the formation of 3-0-/3-L-arabinopyranosyl-L-arabinose (XXXIX). 26 Although this disaccharide has been isolated as an acid-reversion product from L-arab-inose,131 it is accompanied under these conditions by two other arabinose-containing disaccharides, neither of which was detected in the larch polysaccharide hydrolyzate. Since hydrolysis of methylated -galactan gave approximately equimolar proportions of 2,3,4-tri-O-methyl-L-arabinose and 2,5-di-O-methyl-n-arabinose, traces of 2,3,5-tri-O-methyl-L-arabinose, and no mono-O-methyl-L-arabinose, it is clear that the L-arabinose units must arise from an arabinogalactan rather than from an arabinan, and that the majority of these must be present in 3-0-/3-L-arabinopyranosyl-L-arabino-furanose side-chains (XLV) linked, in some way as yet unknown, to the framework of D-galactose units (XLI). 

Hemicelluloses in reaction woods are quite different from those in the normal woods, namely, galactan and P-(l-3)-gIucan in compression wood and galac-tan in tension wood. It is also well known that a remarkable amount of a water-soluble polysaccharide, arabinogalactan, is contained in the heartwood of larch. Since this polysaccharide occurs mainly in the lumen of tracheids and is not a cell wall component, it may not be included in hemicelluloses. Although structures and distributions of hemicelluloses have been comprehensively studied in the last 20 years, their physiologic meanings in a cell wall are not known yet. This must be the most important point for the future study of hemicelluloses. 

D-Galactans.—L-Arabino-D-galactan has been cross-linked with epichlorohydrin and used for affinity chromatographic purification of the lectins from Arachis hypogaeafi and Ricinus communis. Larch arabinogalactan copolymerized with L-leucine JV-carboxyanhydride and then mixed (5 2) with agarose has been used for the purification of the lectin from Tridacna maxima. ... 

The major D-galactan hemicellulose is an arabinogalactan obtained from softwoods such as larch, black spruce, pine, Douglas fir, cedar, and juniper [72]. Western larch is high in arabinogalactan. The larch arabinogalactans have main chains of D-galactopyranosyl units linked P-1 3 with branch chains of... 

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