Actin kinase: a protein kinase that phosphorylates actin of fragmin-actin complex.
Actin of fragmin-actin complex is phosphorylated by an endogenous kinase from plasmodium of Physarum polycephalum. The phosphorylation abolishes the nucleation and capping activities of fragmin-actin complex. The kinase has been purified and termed actin kinase [Furuhashi, K. & Hatano, S. (1990) J. Cell Biol. 111, 1081-1087]. Enzymatic properties of the purified actin kinase were studied in detail. Actin kinase exhibited the highest activity under conditions physiological for the plasmodium (30 mM KCl, 6 mM MgCl2, pH 7.0). The Vmax and the Km of the enzyme for ATP were about 83 mumol/min/mg and 25 microM, respectively. The Km for fragmin-actin complex was 190 nM. The purified actin kinase phosphorylated actin of fragmin-actin complex at a constant rate regardless of Ca2+ concentration. Similarly, 2 microM cAMP, 2 microM cGMP, 2 micrograms/ml calmodulin in the presence of Ca2+ or 1 mM GTP showed no effect on the activity of the purified enzyme. Actin kinase did not phosphorylate histone H1, H2B, alpha-casein, or beta-casein, suggesting that actin kinase is a new kind of protein kinase which specifically phosphorylates actin of the fragmin-actin complex.
Furuhashi
K
K
Department of Molecular Biology, School of Science, Nagoya University, Aichi.
Hatano
S
S
D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D007477:Ions; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000032:analysis*
D000199:Actins; D007477:Ions; D000255:Adenosine Triphosphate; C074377:actin kinase; D017346:Protein Serine-Threonine Kinases