Caldesmon and myosin subfragment-1 act differently on the structural state of 1,5-IAEDANS-modified tropomyosin in ghost muscle fibers

The effect of caldesmon (CD) and subfragment 1 of myosin (S1) on the structural state of tropomyosin (TM) modified with N-(iodoacetyl)-N-(1-naphthyl-5-sulfo)-ethylene-diamine (1.5-IAEDANS) in single myosin-free skeletal muscle fibers was studied using polarized microfluorimetry. S1 was performed from skeletal muscles of rabbits, whereas CD and TM were prepared from the smooth muscle of chicken gizzards. An analysis of experimental data revealed that CD initiates and increases the motility of 1.5-IAEDANS-TM, while S1 decreases it. In the presence of CD S1 binding to actin is accompanied by significant changes in the fluorescent label motility. It is supposed that CD and S1 induce in TM conformational changes which interfere with the protein interaction with F-actin.