Actin filament capping and cleaving activity of cytochalasins B, D, E, and H

The concentration dependences of the activities of cytochalasin B, D, E, and H in capping and cleaving actin filaments have been assayed using fluorescence photobleaching recovery. Filament capping was detected by the increase in mobile G-actin. Cytochalasin D (CD) showed the strongest filament capping activity, with an apparent dissociation constant from filament ends of 50 nM. The order of capping activity was CD greater than CH greater than CE much greater than CB. Filament cleavage was detected by the increase in the diffusion coefficients of actin filaments. By this criterion the order of filament cleavage activity was CD, CE greater than CH much greater than CB. Cytochalasin B shows some activity in cleavage of filaments over a concentration range (0-100 microM) at which it shows no appreciable capping activity. This activity, together with results from other groups, is interpreted to mean that CB binds to protomers within the filament, but not to the barbed end. The reversal of activities for CH and CE, combined with the activity profile of CB, constitute the strongest evidence to date that there is more than one cytochalasin binding site on the actin molecule.