A Myosin-like Protein in the Cortical Layer of Cleaving Starfish Eggs

Abstract

A myosin-like protein, “ovomyosin, ” was extracted from the isolated cortical layer of cleaving starfish eggs. It was purified by ultracentrifugation, ammonium sulfate fractionation, sucrose density gradient centrifugation and precipitation at an ionic strength of 0.2. This enzyme had Ca²⁺-activated ATPase [EC 3. 6. 1. 3] activity and a sedimentation coefficient of 6-7S. The main component of purified ovomyosin fraction showed the same mobility as the heavy chain of rabbit skeletal muscle myosin on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Ovomyosin could form thick filaments in 0.2M KCl. However, rabbit F-actin failed to activate the Mg²⁺-dependent ATPase activity of ovomyosin. The content of ovomyosin in the cortical layer in relation to that of ovoactin and its role in cytokinesis of the starfish egg are discussed.