| Abstract: | Total glycopeptides from human K-562 cells, labeled metabolically with 3H]glucosamine or 3H]mannose, were prepared by extracting the cells with organic solvents to remove lipids and by digesting the residue with pronase. 3H-labeled glycopeptides were fractionated on Sephadex G-50 revealing a high molecular weight fraction (Mr = 7,000 to 11,000), comprising approximately 10% of the 3H]glucosamine and 25% of the 3H]mannose label. Digestion of this glycopeptide fraction with endo-beta-galactosidase from Escherichia freundii, specific for a repeating structure of Gal(beta 1 leads to 4)GlcNAc(beta 1 leads to 3), results in the following four products as resolved by Bio-Gel P-2 gel filtration: 1) a disaccharide with the structure beta-2-deoxy-2-acetamidoglucosyl leads to beta-galactose; 2) a trisaccharide with the structure beta-galactosyl leads to beta-2-deoxy-2-acetamidoglucosyl leads to beta-galactose; 3) a tetrasaccharide with the sequence alpha-N-acetylneuraminyl leads to beta-galactosyl leads to beta-2-deoxy-2-acetamidoglucosyl leads to beta-galactose; and 4) a larger, complex fragment which contains mannose and beta-2-deoxy-2-acetamidoglucose and which is probably the protein linkage region. In addition, visualization of radiolabeled glycoproteins by fluorography on polyacrylamide gels revealed a 105,000-dalton "Band 3"-like glycoprotein and other bands that were sensitive to endo-beta-galactosidase. These results indicate that the K-562 cell line bears a glycopeptide, erythroglycan, which has been found on erythrocytes, and that this polymer is expressed mainly in the fetal form as a linear chain. |
