POLARIZATION OF FLUORESCENTLY LABELED MYOSIN SUBFRAGMENT-1 FULLY OR PARTIALLY DECORATING MUSCLE-FIBERS AND MYOFIBRILS

Fluorescently labeled myosin heads (S1) were added to muscle fibers an d myofibrils at various concentrations. The orientation of the absorpt ion dipole of the dye with respect to the axis of F-actin was calculat ed from polarization of fluorescence which was measured by a novel met hod from video images of muscle. In this method light emitted from mus cle was split by a birefringent crystal into two nonoverlapping images : the first image was created with light polarized in the direction pa rallel to muscle axis, and the second image was created with light pol arized in the direction perpendicular to muscle axis. images were reco rded by high-sensitivity video camera and polarization was calculated from the relative intensity of both images. The method allows measurem ent of the fluorescence polarization from single myofibril irrigated w ith low concentrations of S1 labeled with dye. Orientation was also me asured by fluorescence-detected linear dichroism. The orientation was different when muscle was irrigated with high concentration of S1 (mol ar ratio S1:actin in the I bands equal to 1) then when it was irrigate d with low concentration of S1 (molar ratio S1:actin in the I bands eq ual to 0.32). The results support our earlier proposal that S1 could f orm two different rigor complexes with F-actin depending on the molar ratio of S1:actin.