The Molecular Heterogeneity of Nonspecific Cross‐reacting Antigen Synthesized by Tumor Cells and Granulocytes

The molecular heterogeneity of nonspecific cross‐reacting antigen (NCA) was examined. Metabolically‐labeled glycoproteins were precipitated from cell lysates of human tumor cell lines and of normal peripheral granulocytes with antibodies specific for NCA, and analyzed by SDS‐PAGE. NCA components synthesized by three tumor cell lines, QGP‐1 (pancreas), HLC‐1 (lung) and CAOV‐2 (ovary) showed slightly different migration patterns on SDS‐PAGE, but the molecular weights of their unglycosylated peptides synthesized in the presence of tunicamycin were all found to be 35K. On the other hand, two molecular species of NCA were identified in normal granulocytes: an 80K mature form derived from a 69K precursor peptide and a 58K mature form from a 41K precursor peptide. Upon SDS‐PAGE, the migration pattern of the unglycosylated NCA peptides from tumor cells was affected by the presence of 2‐mercaptoethanol, while that of the peptides of granulocytes was not. All the NCAs identified in this study possessed antigenic determinants common to carcinoembryonic antigen as well as those unique to NCA. These results suggest that the molecular heterogeneity of NCA observed thus far resulted from diverse glycosylation of the three fundamental molecular forms of unglycosylated peptides: one with a molecular weight of 35K produced by tumor cells and two with molecular weights of 69K and 41K produced by granulocytes.