Purification of uterine myosin and synthetic filament formation

Rabbit uterine myosin was purified by DEAE-Sephadex column chromatography. The purified myosin was shown to be free from contamination with actin or other impurities by sodium dodecyl sulfate gel electrophoresis. It was also shown to have two light chains with molecular weights of 22,000 and 17,000. The C protein normally found in crude, rabbit skeletal muscle myosin was not found in crude, rabbit uterine myosin. On reducing the ionic strength of a solution of rabbit uterine myosin, the myosin molecules first aggregated to form short, tapered bipolar filaments with bare zones. These were observed in the presence or absence of 10 m m-magnesium. These filaments ranged in length from 0.3 μm to 0.6 μm. On reaching 0.1 m-KCl, and only if 10 m m-magnesium was present, the filaments grew in length by linear overlap of the tapered bipolar filaments and obliteration of the bare zone regions. These filaments ranged in length from 0.7 μm to 1.2 μm.