Cooperative conformational change in F-actin filament induced by the binding of heavy meromyosin.

The binding of HMM to F-actin containing bound 1, N6-ethenoadenosine diphosphate (epsilon-ADP), a fluorescent analogue of ADP, caused a significant increase in the fluorescence intensity of epsilon-ADP at 410 nm on excitation at 340 nm. This increase is regarded as due to a conformational change in the actin molecule induced by HMM binding. The fluorescence intensity increase was not directly proportional to the amount of bound HMM. This phenomenon suggests that a conformational change in neighbouring actin molecules is induced cooperatively by the conformational change of the actin molecule binding HMM.