Developmental changes in brain glycoproteins.

During the postnatal development of rat brain there are large increases in the concentration of brain glycoproteins. Between 1 and 30 days the greatest changes (70-100%) take place in the levels of glycoprotein mannose, galactose and glucosamine, accompanied by smaller increases (35-55%) in sialic acid and fucose. By 30 days of age levels of brain glycoproteins are within 5% of the adult values. Analyses of the molecular size and composition of glycopeptides prepared from brains of 1- and 30-day-old rats lead to the conclusion that during postnatal brain development there is a preferential synthesis of a distinct population of glycoproteins containing oligosaccharides consisting predominantly of glucosamine, mannose and galactose. These oligosaccharides therefore have a large 'core' segment and a relative deficiency of the characteristically terminal sugars, fucose and sialic acid. In very young rat brain there are also large amounts of a metabolically stable form of glycogen or limit dextrin which accompanies the glycopeptides through the usual methods involved in their preparation from brain glycoproteins. The concentration of this glucose polymer decreases by 93% within 30 days after birth, but its presence even in adult brain is a likely explanation for the numerous reports of small amounts of glucose in brain glycopeptides and glycoproteins.