Fluorescence study of ϵ‐ADP bound to rabbit F‐actin: Structural change in the adenine subsite of F‐actin under the influence of heavy meromyosin

In a recent nanosecond pulse-fluorometric study of Factin+ADP [ 11, it was found that e-ADP is tightly bound in F-actin and the macromolecular motion of Factin is characterised by a correlation time as long as several microseconds. The study is extended in the present work so that the fluorescence of e-ADP bound to F-actin was measured in the presence of an Increasing amount of heavy meromyosin. Both static and time-dependent fluorescence measurements show that binding of heavy meromyosin to F-actin induces a cooperative structural change in the adenine subsite of F-actin. The cooperativity is enhanced by the combination of F-actin-e-ADP with tropomyosin.