Arabinogalactans, molecular weight

StmcturaHy, arabinogalactan is a complex, highly branched polymer of arabinose and galactose in a 1 6 ratio (67). It is composed of one fraction with an average molecular weight of 16,000, and one of 100,000 (68). 

Sepharose 4B) chloride arabinogalactans of high molecular weight (Mw 3 x 10s-3 X 106) ... 

Arabinogalactan occurs as a white to yellow-white, coarse or fine powder. It is the dried water extract from the wood of the larch trees Larix occidentalis and Larix laricina (Fam. Pinaceae). It is a highly branched polysaccharide that has a molecular weight of 15,000 to 60,000 daltons and is composed of galactose units and arabinose units in the approximate ratio of 6 1. It is freely dispersible in hot or cold water. It is insoluble in alcohol. 

Hemicellulose Samples. Two water-soluble hemicellulosic samples were used (1) acetyl-4-O-methylglucuronoxylan (molecular weight = 30,000) from white birchwood, isolated by the extraction of chlorine holocellulose with dimethyl sulfoxide and (2) arabinogalactan, Stractan from St. Regis Paper Company (arabinose galactose = 1 6 molecular weight = 60,000), prepared by the water extraction of heartwood of western larch. Both samples were kindly provided by T. E. Timell (SUNY). 

Wood Solubility. The solubility of wood in various solvents is a measure of the extraneous components content. No single solvent is able to remove all of the extraneous materials. Ether is relatively nonpolar and extracts fats, resins, oils, sterols, and terpenes. Ethanol/ benzene is more polar and extracts most of the ether-solubles plus most of the organic materials insoluble in water. Hot water extracts some inorganic salts and low molecular weight polysaccharides including gums and starches. Water also removes certain hemicelluloses such as the arabinogalactan gum present in larch wood see Table I). 

In 1972, however, Adam et al. 3) showed that hydrosoluble products, obtained by lysozyme treatment of purified cell walls, or delipidated cells were more active than Wax D and cell walls. Among these, the best defined, called WSA (Water Soluble Adjuvant) (enclosed by frame. .. in Fig. 2) has a molecular weight of approximately 20.000 daltons and consists of an arabinogalactan linked to a peptidoglycan. It can also be prepared from Nocardia strains 4) similar products from Mycobacteria where obtained by Migliore and Jolles by autolysis of human strains (52) and by Hiu from hydrogenolysis products of BCG (27). 

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