Structural characterization and biosynthesis of gp87, a melanoma-associated oncofetal antigen defined by monoclonal antibody 140.240

The monoclonal antibody 140.240, which reacts with a melanoma-associated oncofetal antigen, identifies an epitope present on an 87 kd molecule present on the surface of melanoma cells. This molecule is a single-chain monomer, which by tunicamycin treatment and two-dimensional tryptic mapping has been shown to arise from a 77 kd polypeptide precursor (p77). This precursor is rapidly glycosylated to an 83 kd intermediate (gp83) which in turn is rapidly further glycosylated into the mature 87 kd glycopolypeptide (gp87). Neuraminidase treatment of the glycopeptides indicates that only gp87 contains accessible sialic acid moieties.