Calcium Inhibition of Physarum Myosin as Examined by the Recombinant Heavy Mero-Myosin
Plasmodia of Physarum polycephalum shows vigorous cytoplasmic streaming by changing direction every few minutes. This oscillatory streaming is regulated by Ca2+ and is thought to be driven by a conventional myosin, i.e., by a myosin II isoform.1,2 While working as an assistant professor in Professor Ebashi’s laboratory at the University of Tokyo, one of the present authors (K.K.) induced the superprecipitation of actomyosin preparation or myosin B from the plasmodia to examine the effect of Ca2+. It superprecipitated without requiring Ca2+. When Ca2+ at μM level was present, the superprecipitation was inhibited.3 This calcium inhibition was quite the opposite of the superprecipitation of actomyosin from vertebrate muscles,4 and we expected that the inhibitory mode could be involved in the plant cytoplasmic streaming.2 With the finding of the diverse classes of unconventional myosin such as myosin I and V5 in vertebrate muscles, the inhibitory mode was shown to play a role in cell motility in both animal and plant kingdoms. In this case the myosins have calmodulin (CaM) as the light chains and are regulated by interaction of Ca2+ with CaM, which exerts an inhibitory effect on activity.5
KeywordsATPase Activity Regulatory Light Chain Physarum Polycephalum Calcium Inhibition Essential Light Chain
Unable to display preview. Download preview PDF.
- 3.K. Kohama, K. Kobayashi, and S. Mitani, Effects of Ca ion and ADP on superprecipitation of myosin B from slime mold, Physarum polycephalum, Proc. Jpn Acad. 56B, 591–596 (1980).Google Scholar