Structure of Human Skeletal Keratosulfate

Abstract

Abstract Keratosulfate from old human rib cartilage (KS II) was fractionated into two fractions on Bio-Gel P-6 resin. Glutamic acid or glutamine, serine, proline, and galactosamine were concentrated in the higher molecular weight fraction, whereas aspartic acid or asparagine was concentrated in the retarded peak. During alkaline treatment the higher molecular weight fraction became polydisperse through breaking of bonds involving N-acetylgalactosamine as well as serine and threonine. Studies of the action of alkali on KS II in the presence and absence of borohydride have led to the following conclusions: (a) The predominant O-glycosyl group linked to the hydroxyamino acids appears to be N-acetylgalactosamine. (b) A direct Ehrlich's chromogen is produced during the alkaline elimination, which parallels the decrease in seryl and threonyl groups. (c) When KS II or a product of KS II produced by partial hydrolysis with n acetic acid is treated with alkali in the presence of borohydride at 24°, a new ninhydrin-positive fraction is produced after hydrolysis in HCl. This is presumably derived from a 3-substituted N-acetylgalactosamine. The same fraction appears when N-acetylchondrosine or a tetrasaccharide derived from chondroitin 6-sulfate is treated with alkaline borohydride but not when a tetrasaccharide of hyaluronic acid is thus treated. The unknown derivative of N-acetylgalactosamine apparently is a reduction product of the unsaturated chromogen I postulated by Kuhn. (d) The chromogen produced by alkaline elimination appears to be still attached to a high molecular weight product. Therefore, it must be linked in the original substance via an O-glycosidic bond to the hydroxyl groups of the hydroxyamino acids; it is substituted in position 3 and is further linked to position 6 by an alkali-stable bond. The methylpentose of KS II was isolated and characterized as fucose by its methylphenylhydrazone.