Abstract
A factor was separated from a Physarum myosin B preparation of which the superprecipitation was inhibited by Ca ions (Kohama et al. (1980) Proc. Japan Acad. 56B, 591–596). Actomyosin with the factor in the presence of GEDTA superpre cipitated and hydrolyzed ATP faster than in the presence of 10−5M Ca ions. No time lag was required for the factor to exhibit its full activity.