[Study of molecular mechanisms of muscle contraction using polarization fluorometry]

The review summarizes results of studies on the conformational changes in contractile proteins during muscle contraction. The studies were carried out by polarized fluorescence technique in the UV and visible light. The revealed were alterations of actin and myosin in muscle fiber, taking place at various stages of contractile cycle. Transition from a weak binding state of actomyosin to a strong one was accompanied by F-actin subunit rearrangements, with C- and N-terminals moving relative to the core of thin filament. Myosin light chains and 20-kDa domain of myosin head moved in the same direction as C- and N-terminal regions of actin. The flexibility of actin filaments increased, whereas that of C- and N-terminal regions decreased sharply. Actin-myosin interaction changed dramatically tropomyosin flexibility and caused displacement of the protein relative to C- and N-terminals of actin. Actin structure "freezing" by glutaraldehyde or phalloidin, actin cleavage by subtilisin, as well as actin alteration in denervational atrophy inhibited markedly the intramolecular movement and isometric tension of muscle contraction. Besides, troponin-, caldesmon-, calponin-, and myosin-systems, regulating muscle contraction, modified actomyosin rearrangements in a Ca(2+)-dependent manner. The role of the movement of polypeptide chains in contractile proteins during muscle contraction is discussed.