Heterogeneity of sialoglycoproteins purified from normal and malignant cells

We have identified previously a group of sialoglycoproteins with an apparent molecular weight of 110,000, which appear homogeneous by sodium dodecyl sulfate:polyacrylamide gel electrophoresis but exhibit isoelectric point heterogeneity by two-dimensional polyacrylamide gel electrophoresis. This technique demonstrated that there are multiple glycoproteins of similar molecular weight which differ between normal cells and transformants. We have now purified glycoproteins by concanavalin A:Sepharose chromatography and preparative polyacrylamide gel electrophoresis from both a nontumorigenic normal mouse fibroblast line, A31, and a highly malignant nonimmunogenic transformant, 3T12T. Differences in the isoelectric point distribution of the sialoglycoproteins which were observed between the normal and transformed two-dimensional gel patterns using crude membranes could also be demonstrated with the purified glycoproteins. Treatment of the isolated sialoglycoproteins with neuraminidase to remove sialic acid resulted in significant isoelectric point shifts but did not eliminate all of the heterogeneity. Even following neuraminidase treatment, the purified glycoprotein fraction upon isoelectric focusing showed differences in patterns between normal and transformed cells. Preliminary characterization of the alterations seen in the two cell lines are presented and show decreased fucose and increased sialic acid in transformed cell glycoprotein.