Plasma membrane proteins and glycoproteins from chinese hamster cells sensitive and resistant to actinomycin D

Plasma membrane proteins and glycoproteins have been isolated from Chinese hamster cells of the spontaneously transformed DC‐3F parental cell line and the DC‐3F/AD X line with a high level of acquired resistance to actinomycin D. Plasma membrane preparations from both cell lines band at 1.16 g/ml after isopycnic centrifugation. We present evidence to indicate differences in the leucylpeptide backbones of the antibiotic‐sensitive cells and the drug‐resistant DC‐3F/AD X cells. In addition, there are differences in the plasma membrane glycopeptides of the two cell lines as revealed by sodium dodecyl gel electrophoresis. Drug‐resistant cells synthesize a surface glycopeptide which is much larger than the major one present on the drug‐sensitive cells. Both of these cell lines are devoid of 5′‐nucleotidase and alkaline phosphatase activities. The role of plasma membrane protein differences in drug‐resistant cells is discussed.