title: Role of actin in the myosin-linked Ca(2+)-regulation of ATP-dependent interaction between actin and myosin of a lower eukaryote, Physarum polycephalum.
abstract: Actin-activated ATPase activity of myosin from Physarum polycephalum decreases when it binds Ca2+ and increases when it loses Ca2+. This Ca-inhibition is observed with phosphorylated myosin [Kohama, K. (1990) Trend, Pharmacol. Sci. 11, 433-435]. The activity of dephosphorylated myosin remained at a low level both in the presence and absence of Ca2+, although Ca(2+)-binding ability was much the same as that of the phosphorylated myosin. The effect of phosphorylation has been studied at a conventional actin concentration, which is comparable with that of myosin by weight. When the concentration of actin was increased by 10 times, the dephosphorylated myosin became actin-activatable in the absence of Ca2+, and Ca-inhibition was recovered. As actin exists quite abundantly in non-muscle cells of Physarum, myosin phosphorylation plays virtually no role in regulating actin-myosin-ATP interaction in vivo. Physiologically the interaction may be regulated by Ca2+ by binding to and subsequent release from myosin. Latex beads coated by either phosphorylated or dephosphorylated myosin moved ATP-dependently on the actin cables of Characeae cells to the same extent in the absence of Ca2+, but the movement was abolished by increasing Ca2+. When the interaction was examined by monitoring the movement of actin filaments on myosin fixed on a coverslip, the movement and Ca-inhibition of the movement were detected with phosphorylated, not dephosphorylated, myosin [Okagaki, T., Higashi-Fujime, S., & Kohama, K. (1989) J. Biochem. 106, 955-957].(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology, Gunma University School of Medicine.
authors.forename: K
authors.initials: K
authors.lastname: Kohama
authors.forename: T
authors.initials: T
authors.lastname: Kohno
authors.forename: T
authors.initials: T
authors.lastname: Okagaki
authors.forename: T
authors.initials: T
authors.lastname: Shimmen
mesh_terms: D000199:Actins / Q000378:metabolism / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D004789:Enzyme Activation; D007700:Kinetics; D009218:Myosins / Q000378:metabolism* / Q000502:physiology*; D010766:Phosphorylation; D016839:Physarum polycephalum / Q000378:metabolism*
chemical_list: D000199:Actins; D000255:Adenosine Triphosphate; D009218:Myosins; D002118:Calcium