title: Acanthamoeba cofactor protein is a heavy chain kinase required for actin activation of the Mg2+-ATPase activity of Acanthamoeba myosin I.
abstract: We have purified a cofactor protein previously shown (Pollard, T. D., and Korn, E. D. (1973) J. Biol. Chem. 248, 4691-4697) to be required for actin activation of the Mg2+-ATPase activity of Acanthamoeba myosin I. The purified cofactor protein is a novel myosin kinase that phosphorylates the single heavy chain, but neither of the two light chains, of Acanthamoeba myosin I. Phosphorylation of Acanthamoeba myosin I by the purified cofactor protein requires ATP and Mg2+ but is Ca2+-independent. The Mg2+-ATPase activity of phosphorylated Acanthamoeba myosin I is highly activated by F-actin in the absence of cofactor protein. Actin-activated Mg2+-ATPase activity is lost when phosphorylated Acanthamoeba myosin I is dephosphorylated by platelet phosphatase. Phosphorylation and dephosphorylation have no effect on the (K+,EDTA)-ATPase and Ca2+-ATPase activities of Acanthamoeba myosin I. These results show that cofactor protein is an Acanthamoeba myosin I heavy chain kinase and that phosphorylation of the heavy chain of this myosin is required for actin activation of its Mg2+-ATPase activity.
mesh_terms: D000199:Actins / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000656:Amoeba / Q000201:enzymology*; D000818:Animals; D004789:Enzyme Activation; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D009218:Myosins / Q000302:isolation & purification / Q000378:metabolism*; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D000199:Actins; D011494:Protein Kinases; D000251:Adenosine Triphosphatases; D009218:Myosins; D008274:Magnesium