Abstract
Lipid-extracted, proteinase-treated, and dialyzed homogenates of human brain were subjected to acidic resin hydrolysis. Paper chromatography of the hydrolyzate gave (besides spots of several hexuronic acids, galactose, glucose, mannose, and fucose) two pentose spots which had R f values of arabinose and xylose in three different solvent systems. Further investigations by independent methods to confirm the presence of an arabinose containing polymer gave the following results: (1) Chromatograms of the acetylated brain hydrolyzate showed spots indiscernible from those of the tetraacetate of authentic arabinose. (2) Partition chromatography of the hydrolyzate on a Celite column gave arabinose as a well-separated fraction. The position of this fraction in the eluate was identical with that of known arabinose in a standard monosaccharide mixture fractionized by the same procedure. (3) Crystalline arabinose diphenylhydrazone and arabinose dichlorophenylhydrazone obtained from brain hydrolyzates were identical with analogous preparations obtained from known l-arabinose. The dichlorophenylhydrazone of brain arabinose depressed the melting point of the dichlorophenylhydrazone of authentic d-arabinose and did not depress the melting point of the analogous derivative prepared from authentic l-arabinose, indicating the presence of l-arabinose. (4) The presence of galacturonic acid in brain heteropolysaccharides was established by previous experiments. The possibility was excluded that the arabinose found was formed from this galacturonic acid by the hydrolytic procedure. Control experiments showed that the procedure used for hydrolysis does not convert galacturonic acid to arabinose. The investigated macromolecular brain fraction contains both galacturonic acid and arabinose residues. (5) The arabinose containing heteropolysaccharide fraction is precipitable with cetyl pyridinium bromide and contains, besides hexosamines and hexuronic acids, hexoses and amino acid residues.
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