Variations and Distributions of O-Glycosidically Linked Sugar Chains in Bovine κ-Casein

The variation and distribution of O-glycosidically linked sugar chains in κ-casein from bovine mature milk were analyzed by HPLC, fast atom bombardment mass spectrometry, and ¹³C nuclear magnetic resonance. A monosaccharide alditol (N-acetylgalactosaminitol) and four oligosaccharide alditols [a neutral disaccharide (galactosyl-β1-3N-acetylgalactosaminitol), two acidic trisaccharides (straight chain: N-acetylneuraminyl α2-3galactosyl-β1-3N-acetylgalactosaminitol and branch chain: galactosyl β1-3 (N-acetylneuraminyl α2-6)N-acetylgalactosaminitol), and an acidic tetrasaccharide (N-acetylneuraminyl α2-3galactosyl-β1-3(N-acetylgalactosaminyl α2-6)N-acetylgalactosaminitol] were identified as sugar chains linking on normal bovine κ-casein. The most dominant sugar chain was an acidic tetrasaccharide. The four oligosaccharide chains were identical to those already found, but N-acetylgalactosamine was a newly identified sugar chain linking on κ-casein. The distribution of monosaccharide, disaccharide, trisaccharide (straight), trisaccharide (branched), and tetrasaccharide chains were determined by HPLC to be .8, 6.3, 18.4, 18.5, and 56.0%, respectively (means of five κ-caseins).