Control of ciliary activity in paramecium--IV. Ca2+ modification of Mg2+ dependent dynein ATPase activity.

1. Dynein proteins were solubilized from demembranated cilia of Paramecium by extraction at high ionic strength. 2. Mg2+-dependent ATPase (EC 3.6.1.3) activity of crude dynein extracts was inhibited by micromolar concentrations of Ca2+ ions. 3. Sepharose 4B chromatography of the crude extracts yields three dynein fractions. The major fraction contains a single protein and is insensitive to Ca2+ ions. Two other fractions, both heterogeneous in composition, show opposing Ca2+ ion sensitivity expressed as a Ca2+ dependent alteration in MgATP2- dependent ATPase activity. The Ca2+ ion sensitive forms show altered electrophoretic mobility on native polyacrylamide gels in the presence and absence of Ca2+ ions. 4. The data provides evidence for a Ca2+ ion dependent concomitant alteration in both molecular form and hydrolytic activity of the dyneins. The results are discussed in terms of a possible molecular mechanism for Ca ion regulation of ciliary activity in terms of the sliding microtubule model.