Sulfated glycoproteins secreted by human vascular endothelial cells

Endothelial cells incorporate 35SO4 into a class of glycoproteins which are released from the cell layer into the culture medium. The incorporated 35SO4 was localized on intact oligosaccharide chains which were released from the protein either chemically by hydrazinolysis or enzymatically by a peptide: N-glycosidase activity; thus these 35S-oligosaccharides are presumably N-glycosidically linked to protein. These 35S-oligosaccharides were also isolated and analyzed as labeled glycopeptides and found to contain the terminal trisaccharide sequence sialic acid leads to galactose leads to N-acetylglucosamine. After removal of these carbohydrate residues, the remainder of this 35S-glycopeptide was susceptible to alpha-mannosidase digestion yielding a smaller 35 S-glycopeptide containing GlcNAc35SO4. Monensin (10(-8) M), a monovalent cation ionophore, inhibited the sulfation (greater than 80%) and synthesis (greater than 60%) of endothelial cell-sulfated proteoglycans which were released into the culture medium. However, neither the synthesis nor sulfation of cell-released 35S-glycoproteins was affected at similar monensin concentrations. Higher concentrations of monensin (greater 5 X 10(-8) M) inhibited the incorporation of both [3H]glucosamine and 35SO4 into cell-released glycoproteins.U