Studies on HeLa cells surface glycopeptides alterations in membrane structure during the cell cycle.

Limited exposure of intact HeLa cells to proteolytic enzymes results in the release of fragments of membrane glycoproteins in the form of glycopeptides. Enriched and partially purified fractions from these glycopeptides are potent inhibitors of protein synthesis in cell-free systems and in intact cells. A comparison of the in vivo and in vitro response revealed that a substantial proportion of protein synthesis in intact cells is resistant to inhibition. When HeLa cell surface glycopeptides (HSP) induced inhibition of protein synthesis was studied in synchronized cell cultures it was found that G1 phase cells are most sensitive to HSP. A cell cycle dependent alteration in the availability of HSP to protease release was also observed. Cells in S phase yield the greatest amount of HSP upon limited proteolysis. The data suggest that alterations in membrane structure at the termination of S phase result in a conversion of membrane glycoproteins from a protease sensitive to a protease resistant state.