Compositional patterns of sialofucohexosaminoglycans derived from rat brain glycoproteins

Abstract

Glycoproteins in whole rat brain were assayed by determining the carbohydrate content of the glycopeptides released by the proteolytic action of papain on the defatted protein residue which remained after extraction of the tissue with chloroformmethanol (2:1 and 1:2, v/v). Dialyzable and nondialyzable glycopeptides (sialofucohexosaminoglycans) were released by proteolysis. The N-acetylneuraminic acid (NANA) content of the solubilized sialofucohexosaminoglycans and the gangliosides account for 28 and 65%, respectively of the total NANA recovered from the tissue. The remaining NANA is accounted for by free NANA (3%) and NANA that is bound in a papain-resistant fraction (4%). Fractionation of the nondialyzable sialofucohexosaminoglycans by column electrophoresis yielded six fractions which were characterized by an increase in NANA content, a decrease in fucose content, and an increase in electrophoretic mobility as the molecular size of the fraction increased. The six fractions consisted of components which had a molecular size that corresponded to a molecular weight of 9900-13,500 as judged by gel filtration. The sugar components consisted of NANA, fucose, galactose, mannose, glucosamine, and galactosamine. Ninety-five percent of the hexosamine was glucosamine. The hexose/hexosamine ratio for five of the six fractions was 1.34. One of the fractions contained two molecules of hexose per mole of hexosamine. The dialyzable sialofucohexosaminoglycans were separated into three fractions by gel filtration. The three fractions consisted of components which had a molecular size corresponding to a molecular weight of 6000 or less. The smallest component lacked fucose. Dialyzable Sialofucohexosaminoglycans contained the same carbohydrates as the nondialyzable Sialofucohexosaminoglycans, except that a higher proportion of the hexosamine and hexose residues, respectively consisted of galactosamine and mannose.