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 Lewis a ‐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 > 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