On the molecular basis of action of cytochalasin B

Tritium‐labeled cytochalasin B binds rapidly and reversibly to mammalian cells, and a class of high‐affinity sites (K n ≅ 10 −7 M) and a class of low‐affinity sites (K D ⩾ 10 −5 M) are detected. In red blood cells, the high‐affinity binding sites (about 3 × 10 5 per cell) are associated with the plasma membrane, and at least 80% of these appear to be intimately related to the glucose transport system. Fractionation of cellular components of platelets by differential centrifugation and gel filtration chromatography reveals that the high‐affinity binding sites in these cells are also associated with membranous materials. A substantial number of the low‐affinity binding sites can be traced to platelet actin. The binding of cytochalasin B to actin is consistent with the alteration of intrinsic viscosity and morphology of actin filaments in vitro by the compound at concentrations of around 10 −5 ‐10 −4 M. The interaction of cytochalasin B with actin may account for its inhibitory effect on various forms of cell motility.