CALDESMON AND MYOSIN SUBFRAGMENT-1 HAVE DIFFERENT EFFECTS ON THE STRUCTURAL STATE OF TROPOMYOSIN MODIFIED WITH 1,5-IAEDANS IN GHOST MUSCLE-FIBERS

Polarization microfluorometry in ghost muscle fibers free of myosin, tropomyosin (TM), and troponin, obtained from glycerinized rabbit lumbar muscles, was used to investigate the structural state of TM modified by N-(iodoacetyl)-N'-(1-naphthyl-5-sulfo)-ethylenediamine (1,5-IAEDANS) during binding to thin strands of myosin subfragment 1 (S1) and/or caldesmon (CD). Preparation of S1 were obtained from rabbit skeletal muscles, while preparations of CD and TM were obtained from smooth muscles of chicken gizzard. An analysis of the experimental data indicates that CD initiates an increase, while S1 initiates a decrease in the mobility of 1,5-IAEDANS in the thin strands. In the presence of CD, the binding of S1 to actin is not accompanied by any appreciable change in the mobility of the fluorescent label. It is suggested that CD and S1 induce conformational changes in TM that are accompanied by changes in its interaction with F-actin.