The effect of caldesmon and tropomyosin from smooth muscles on the motility of myosin head in ghost muscle fibers

: The effects of caldesmon and smooth muscle tropomyosin on the motility of myosin subfragment I (SI) modified by N-(iodoacetyl)-N'-(1-naphtyl-5-sulfo)-ethylenediamine (1.5-IAEDANS) was studied in myosin-, troponin- and tropomyosin-free rabbit ghost muscle fibers using the polarized microphotometry technique. It was found that the fluorescence anisotropy initiated by the 1.5-IAEDANS-SI arrangement in the fibers is higher in the presence of tropomyosin than in its absence. Caldesmon diminishes the fluorescence anisotropy of the fibers. Data from a kinetic analysis suggest that the motility of fluorophores in the presence of tropomyosin in thin filaments is markedly decreased. Caldesmon weakens the effect of tropomyosin on the fluorescent label motility. It was supposed that caldesmon and tropomyosin initiate conformational changes in myosin heads which are accompanied by loosening or strengthening of their bonds with F-actin, respectively. Caldesmon inhibits the effect induced by tropomyosin.