[Structural changes in muscle fiber contractile proteins studied by polarization ultraviolet fluorescence microscopy. VI. Conformational restructurings of F-actin induced by the binding of heavy meromyosin].

Decrease in tryptophan fluorescence anisotropy of a single ghost muscle fibre was found at the binding of heavy meromyosin (HMM) to actin. Polarized fluorescence revealed its peak changes at a molar ratio of HMM/actin equal to 0.1. The changes observed in polarized fluorescence at F-actin-HMM interaction were found to depend on the state of HMM. The changes in anisotropy fluorescence under the same conditions were assumed to be independent of tryptophane residues in HMM, reflecting cooperative changes in F-actin conformation. Changes in the conformation of F-actin are of great importance in muscular contraction.