Accessibility of plasma membrane sialoglycoconjugates of Novikoff tumor cells to exogenous neuraminidase and proteases.

Plasma membrane glycoconjugates of Novikoff tumor cells were radioactively labeled by oxidation with NaIO4 followed by reduction with NaB3H4 Submission of the radioactively labeled glycoconjugates to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate followed by fluorography revealed the presence of at least ten major glycoproteins and a glycolipid fraction. The glycolipid fraction contained 34% of the cell-surface radioactive label. Pretreatment of cells with neuraminidase from Vibrio cholerae reduced radioactive labeling of the glycoproteins by 71% and that of the glycolipids by 39%. Sequential treatment of cells with papain and neuraminidase further reduced radioactive labeling of the glycolipid fraction, indicating that resistance of this fraction to the hydrolytic action of neuraminidase was determined, at least in part, by steric factors. Incubation of cells with papain resulted in extensive degradation of most of the radioactively labeled glycoproteins with the exception of a subset of glycoproteins having apparent molecular weights of 48 000 +/- 5000. Trypsin was more selective, degrading three glycoproteins having apparent molecular weights of 200 000, 140 000 and 37 000.