Structure of tumor-associated carbohydrate antigen Ca 19-9 on human seminal-plasma glycoproteins from healthy donors.

The monoclonal antibody-defined, tumor-associated antigen Ca 19-9, chemically identical with the sialylated Lewisa-carbohydrate determinant of a monoganglioside and a mucin, was demonstrated by radioimmunoassay to be present in large amounts as component of fucose-rich sialoglycoproteins, which had been extracted from human seminal plasma of healthy donors. The carbohydrate antigen of these glycoproteins (m greater than 205 kDa and m 115 kDa), which are presumably secreted by the prostatic gland, was absent in seminal plasma from blood-group-Lewis-negative men. The Ca 19-9 active sialyl-oligosaccharide was cleaved from the proteins by mild alkaline borohydride treatment and was shown to chromatograph on gradient elution from DEAE-Sephadex with the fraction of monosialylated saccharide alditols (MS-SP). The asialo derivative of the major saccharide alditol in this fraction was composed of L-fucose, D-galactose, N-acetyl-D-glucosamine and N-acetyl-D-galactosaminitol in the molar proportions 1:2:1:1 and chromatographed on Bio-Gel P2 according to approximately seven hexose units. A methylation analysis of the sialylated saccharide alditol in fraction MS-SP, which had been purified by high-pressure liquid chromatography, revealed the presence of terminal, non-reducing L-fucose, 3-O-substituted D-galactose, 3,4 di-O-substituted N-acetyl-D-glucosamine and 3-O-substituted N-acetyl-D-galactosaminitol. The presented data and the fragmentation pattern obtained on direct probe EI and FAB+ mass spectrometry of the permethylated asialo derivative are in accordance with the structure of a sialylated pentasaccharide alditol (formula; see text).