title: New states of actomyosin.
abstract: Unstained frozen hydrated samples of myosin subfragment 1 (S-1) cross-linked to actin with the zero-length cross-linker 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide have been examined by electron microscopy in an effort to probe structural states of the attached cross-bridge. The cross-linked complex in the absence of ATP has a rigor-like appearance. In contrast, both in the presence of ATP and after the N, N'-p-phenylenedimaleimide (pPDM) bridging of the reactive thiols of S-1, the covalently attached cross-bridges of the acto X S-1 complex appear more disordered and no longer assume the characteristic rigor 45 degrees angle with the actin filaments. The images both in the presence and absence of ATP bear a striking resemblance to those obtained by negative staining of the cross-linked acto X S-1 complex (Craig, R., Greene, L. E. & Eisenberg, E. (1985) Proc. Natl. Acad. Sci. U.S. A. 82, 3247-3251). The actin-bound pPDM S-1 complex, formed by treating the cross-linked complex with pPDM in the presence of ATP, is an expected analog of the weakly bound cross-bridge state. The disordered appearance of S-1 molecules of the cross-linked complex in the presence of ATP and after pPDM treatment may reflect the structural state of the weakly bound cross-bridge.
mesh_terms: D000199:Actins / Q000378:metabolism; D000205:Actomyosin / Q000378:metabolism*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D005022:Ethyldimethylaminopropyl Carbodiimide / Q000494:pharmacology; D007700:Kinetics; D008301:Maleimides / Q000494:pharmacology; D008854:Microscopy, Electron; D009132:Muscles / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D011817:Rabbits
chemical_list: D000199:Actins; D003432:Cross-Linking Reagents; D008301:Maleimides; D000205:Actomyosin; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins; D005022:Ethyldimethylaminopropyl Carbodiimide; C023860:N,N'-2-phenylenedimaleimide