Isolation and chemical characterization of a cell-surface sialoglycopeptide fraction from novikoff ascites cells.

Abstract

Summary Sialic acid has been shown to contribute significantly to the cell-surface charge of tumor cells. In order to elucidate the chemical nature of the sialic acid-containing molecules present on the tumor cell surface, a procedure for the isolation of a sialoglycopeptide fraction from the surface of Novikoff ascites cells has been developed. Digestion of tumor cell suspensions with papain liberates a sialoglycopeptide fraction from the cell surface. This fraction was partially purified using trichloroacetic acid precipitation, dialysis, and gel filtration on Sephadex G-50. The sialoglycopeptide fraction contains 65–80% of the neuraminidase-labile sialic acid present on the surface of these cells. Quantitative analysis of the composition of this fraction revealed the presence of the following monosaccharides, expressed per mg glycopeptide: 0.39 µmole sialic acid, 0.41 µmole glucosamine, 0.23 µmole galactosamine, 0.15 µmole mannose, 0.54 µmole galactose, 0.53 µmole glucose, and 0.15 µmole uronic acid. Amino acid analysis indicated a peptide content of 15%. Amino acids present in the highest amounts were threonine, aspartic acid, glutamic acid, serine, proline, alanine, and valine (molar ratio, 4:2:1.5:1:1:1:1).