Three-dimensional image analysis of the complex of thin filaments and myosin molecules from skeletal muscle. III. The multi-domain structure of actin-heavy meromyosin complex.

Heavy meromyosin (HMM) prepared by chymotryptic digestion retains DTNB light chain and subfragment-2 (S2) in addition to the two subfragment-1 (S1) moieties. The electron micrograph of negatively stained rigor complex of HMM and actin showed some different features as compared with that of S1 and actin. The three-dimensional image reconstructed from the electron micrograph of actin-HMM gave additional domains other than those observed in actin-S1 (Wakabayashi and Toyoshima, 1981). The differences between the images of actin-HMM and actin-S1 were attributed to the differences in protein composition. Further, the structural characteristics of actin-HMM are discussed in comparison with those of the actin-S1.