QUALITATIVE-ANALYSIS OF THE CARBOHYDRATE-COMPOSITION OF APOLIPOPROTEIN-H

The specific binding of digoxigenin-labeled lectins to carbohydrate mo ieties is used to characterize the carbohydrate chains bound to apolip oprotein H. Our results show that apolipoprotein H is rich in sialic a cid linked alpha(2-6) to galactose or N-acetylgalactosamine. Sialic ac id is not alpha(2-3)-linked to galactose. Galactose is beta(1-4)-linke d to N-acetylglucosamine and beta(1-3)-linked to N-acetylgalactosamine . High-mannose N-glycan chains are barely detectable. After N-glycosid ase F treatment the molecular weight is substantially reduced. The mai n band is 32,500 daltons. Carbohydrate O-linked chains, which are main ly represented by sialic acid, are alpha(2-6)-linked to galactose or N -acetylgalactosamine, Galactose is also organized in O-linked chains a nd it is beta(1-4)-linked to N-acetylglucosamine and beta(1-3)-linked to acetylgalactosamine. Biochemical analysis of carbohydrate structure s reveals that no specific carbohydrate complex is bound to a single i soform.