Three samples of carcinoembryonic antigens were purified from liver metastases of primary colon cancer. The asparagine-linked sugar chains of carcinoembryonic antigens (CEA) were released as oligosaccharides by hydrazinolysis and the structures of oligosaccharides, thus obtained, was studied in combination with methylation analysis and several limited exoglycosidase digestions. All three CEAs contain approximately 25 asparagine-linked sugar chains in one molecule and about 10% of them was high mannose type. However, structural features of the outer chain moieties of the remaining complex-type sugar chains were different by CEA samples. The complex-type sugar chains were mono-, bi-, tri-, and tetraantennary with Manα1→6(±GlcNAcβ1→4)(Manα1→3)Manβ1→4GlcNAcβ1→4(±Fucα1→6)GlcNAc as their cores, half of which were bisected; 86% of their proximal N-acetylglucosamine was fucosylated. The major outer chains in two samples were N-acetyllactosamine and Galβ1→4(Fucα1→3)GlcNAc (X-antigenic determinant) and the remaining one sample contained Fucα1→2Galβ1→4(Fucα1→3)GlcNAc (Y-antigenic determinant) as an additional major outer chain. Furthermore, small amounts of type 1 chain and Lea antigenic determinant were found in some samples. Acidic oligosaccharides consisted of sialic acid containing fractions and sialidase-resistant fractions, and their contents seemed to be in a reciprocal relationship. Sialic acid was linked at the C-3 and C-6 positions of the nonreducing terminal galactose residues of the outer chains.
This work was supported in part by a Grant-in-Aid for Special Project Research (Cancer-Bioscience) and a Grant-in-Aid for Cancer Research from the Ministry of Education, Science and Culture of Japan.