Distribution and age-dependent concentration in brain tissue of glycoproteins containing N-acetylgalactosamine

Glycoproteins that yield non-dialyzable, alkali-labile, N-acetylgalactosamine-containing heteropolysaccharides upon proteolytic digestion show a threefold enrichment in white matter relative to gray matter. Approximately 50% of these glycoproteins appear in soluble extracts prepared from rat brain. This distribution contrasts with that of the predominant alkali-stable sialoglycopeptides, which account for 60% of the total brain glycoprotein-carbohydrate. The latter glycopeptides showed a twofold enrichment in gray matter compared with white, and only about 10% of the glycoproteins that yield these glycopeptides could be solubilized by extraction with aqueous solvents. The concentration of the N-acetylgalactosamine-containing glycoproteins in the 3-year-old cerebral gray matter from human brain was respectively 7-15 and 15-30 times greater than in 8- and 72-year-old tissue. Electrophoretic analysis of the non-dialyzable, alkali-stable, acidic glycopeptides that contain NANA, fucose, mannose, galactose, and N-acetylglucosamine, obtained from the microsomal and synaptosomal fractions, revealed that the composition of these glycopeptides in the two fractions was identical.