Partial purification of two myosin heavy chain kinases from Dictyostelium discoideum

Myosin heavy chain kinase activity was identified in the high speed supernate of lysed Dictyostelium amoebae and was precipitated by 30-50% ammonium sulphate. In low ionic strength buffer, the activity bound tightly to a Cibacron Blue Sepharose column and eluted as a single peak with 1.0 M NaCl. Gel filtration chromatography resolved the kinase into two activities, each of which phosphorylated the tail portion of purified Dictyostelium myosin. One of these activities phosphorylated both serine and threonine residues of the heavy chain, while the other activity only phosphorylated threonine residues. Peptide mapping studies indicated that in vivo and in vitro phosphorylation sites were identical. The heavy chain kinases required Mg2+ for activity but were unaffected by Ca2+ or calmodulin. The heavy chain kinases did not phosphorylate Dictyostelium light chain, and also did not phosphorylate myosins from striated, smooth, or other nonmuscle sources.