Structural studies on glycoprotein oligosaccharides of chromaffin granule membranes and dopamine beta-hydroxylase.
Dopamine beta-hydroxylase present in the soluble matrix of bovine adrenal medullary chromaffin granules contains biantennary complex oligosaccharides and high-mannose oligosaccharides in a molar ratio of approximately 2:1. The high-mannose oligosaccharides contain an average of six mannose residues. The largest biantennary oligosaccharides (40% of the total) have two complete peripheral branches consisting of sialic acid-galactose-N-acetylglucosamine, but an equal proportion lack sialic acid on one branch and the remainder lack N-acetylglucosamine and/or galactose. Affinity chromatography on lentil lectin-agarose demonstrated that 84% of the dopamine beta-hydroxylase biantennary oligosaccharides are substituted by fucose on the core N-acetylglucosamine which is linked to asparagine. Based on carbohydrate concentration and the proportions of biantennary and high-mannose oligosaccharides, it would appear that the four dopamine beta-hydroxylase subunits of Mr congruent to 75,000 are not identical with respect to their oligosaccharide moieties. In chromaffin granule membranes, high-mannose and biantennary oligosaccharides comprise 20 and 35%, respectively, of the glycoprotein carbohydrate. Almost 40% is present in the form of large complex oligosaccharides with three or more antennas, less than 3% of which have both a core fucose residue and a 2,6-substituted alpha-linked mannose residue. Chromaffin granule membranes also contain a small proportion (approximately 6%) of O-glycosidically linked glycoprotein oligosaccharides which are predominantly monosialyl derivatives of galactosyl-N-acetylgalactosamine. The ratio of N-acetyl- to N-glycolylneuraminic acid in dopamine beta-hydroxylase and the glycoproteins of chromaffin granule membranes is approximately 1.5:1, which is within the same range as that previously found in membrane gangliosides and in the chromogranins isolated from the soluble granule matrix.
D000313:Adrenal Medulla / Q000032:analysis; D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D002837:Chromaffin Granules / Q000032:analysis*; D002838:Chromaffin System / Q000032:analysis*; D004299:Dopamine beta-Hydroxylase / Q000302:isolation & purification*; D006023:Glycoproteins / Q000302:isolation & purification*; D007425:Intracellular Membranes / Q000032:analysis; D009844:Oligosaccharides / Q000302:isolation & purification*
D006023:Glycoproteins; D009844:Oligosaccharides; D004299:Dopamine beta-Hydroxylase