SYNTHETIC MYOSIN FILAMENTS FROM VERTEBRATE SMOOTH MUSCLE

A comparison is made between synthetic myosin filaments from smooth muscle of chicken gizzard and those from striated muscle (chicken breast). The filaments were formed by rapid dilution of the KCl concentration to 0.3, 0.2 and 0.1 M at pH values ranging from 8.0 to 6.0. Negative staining was used for electron microscopy. Preparations were also examined in the ultracentrifuge. For both types of myosin the aggregation process is dependent on pH and ionic concentration. Short aggregates are first formed, growing in size on dilution of the KCl to 0.1 M, but reaching longer lengths at the lower pH values. A striking difference between myosin filaments from smooth and striated muscle is that the former grow to a final length (0.6 μ av.) which is about one third that of the latter at pH 6.5 in 0.1 M-KCl. The smooth muscle filaments resemble fairly closely filaments from blended preparations of smooth muscle (Needham & Shoenberg, 1967; Kelly & Rice, 1968). The pattern of aggregation appears to be the same for both types of myosin according to the Huxley (1963) model. Why the aggregation ceases at a certain point, forming lengths that differ in the two types of myosin, could be related to structural differences such as the number of specific bonds available for self-assembly. © 1969.