Subcellular localization of binding sites for cytochalasin D: Evidence from activation energies

The activation energies for binding of tritiated cytochalasin D to HEp-2 cells and isolated plasma membrane were determined by Arrhenius plots. The higher value for intact cells (24 kcal/mol) compared to the plasma membrane fraction (4 kcal/mol at > 11.5 °C, 18 kcal/mol at < 11.5 °C) was taken as evidence that ³H]cytochalasin D must penetrate the plasma membrane in order to reach its binding sites. The data support the conclusion that binding sites for ³H]cytochalasin D are intracellular, on the cytoplasmic face of the plasma membrane (rather than within the lipid bilayer), and on microsomes (endomembranes).