On the mechanism for inactivation of cytochalasin binding activity associated with F-actin and spectrin-band 4.1-actin complex by sulfhydryl reagents.

The sulfhydryl group modifying reagent, p-hydroxymercuribenzoate, inhibited the cytochalasin binding activity of the actin nuclei in the spectrin-band 4.1-actin complex from the erythrocyte membrane and of muscle F-actin. Kinetic studies indicated that while the cytochalasin binding activity was immediately inhibited, the actin remained filamentous and depolymerized slowly over a period of 1 to 2 h. Scatchard analysis of the binding data revealed that initially only the KD was affected. However, prolonged incubation led to depolymerization of the F-actin and dissociation of the spectrin-band 4.1-actin complex, resulting in loss of binding sites. It thus appears that certain actin sulfhydryl group(s) are important for cytochalasin binding. However, the most reactive sulfhydryl group (cys-374) on actin does not appear to be involved.