CELL MITOTIC CYCLE SYNTHESIS OF NIL HAMSTER GLYCOLIPIDS INCLUDING THE FORSSMAN ANTIGEN

Abstract

The synthesis of phospholipids and glycolipids during the cell mitotic cycle of an established hamster line, NIL, has been studied. Cells were synchronized with excess thymidine and mitotically harvested by shaking. Cells were radioactively labeled for 4 h with palmitate, glucosamine, or galactose. Lipids were analyzed by thin-layer chromatography. As cells progressed through the mitotic cycle, incorporation into phospholipids increased but the fraction represented by each remained constant. Similarly, ceramide monohexoside, dihexoside, and hematoside were labeled equally in all phases. Ceramide trihexoside and tetrahexoside were labeled only during G1 and S. Ceramide pentahexoside (the Forssman antigen) shows density-dependent synthesis, accumulation, and reactivity. Ceramide pentahexoside was labeled during all phases of the mitotic cycle but the rate of incorporation decreased in S and G2. The total amount of lipid assayed immunologically in cell extracts gradually increased. Exposure of the Forssman antigen in untreated or trypsin-treated cells was studied using binding of chemically labeled antiForssman antiserum. The amount of antigen detected in trypsinized cells increased during G1 and early S but then remained constant. Mitotic cells exposed all detectable antigen. As cells progressed through the mitotic cycle, a large fraction of the Forssman antigen became cryptic.