title: Effect of troponin-tropomyosin complex and Ca2+ on conformational changes in F-actin induced by myosin subfragment-1.
abstract: The interaction of regulated and unregulated actin of myosin-free ghost single fibre with myosin subfragment-1 free of 5,5'-dithiobis(2-nitrobenzoic acid) light chains was investigated by polarized microphotometry. The anisotropy of intrinsic tryptophan fluorescence of regulated actin is Ca2+-dependent and has a maximal value at low (pCa greater than or equal to 7) and a minimal value at high (pCa less than or equal to 6) concentrations of Ca2+. The interaction of myosin subfragment-1 with actin induces cooperative changes in actin structure, which manifest themselves in a decrease in the anisotropy of tryptophan fluorescence. The cooperativity of conformational changes in actin, induced by myosin subfragment-1, is high for regulated actin in the absence of Ca2+ and low for unregulated and regulated actin in the presence of Ca2+. The data obtained suggest that the decrease of the flexibility of actin filaments, induced by tropomyosin or by Ca-unsaturated troponin-tropomyosin complex, results in increased cooperativity of conformational changes of actin induced by myosin subfragment-1.
mesh_terms: D000199:Actins; D000818:Animals; D001718:Birefringence; D002118:Calcium; D055598:Chemical Phenomena; D002621:Chemistry; D005454:Fluorescence Polarization; D015879:Myosin Subfragments; D009218:Myosins; D010446:Peptide Fragments; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D013329:Structure-Activity Relationship; D014335:Tropomyosin; D014336:Troponin; D014364:Tryptophan
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D014335:Tropomyosin; D014336:Troponin; D014364:Tryptophan; D009218:Myosins; D002118:Calcium