Calcium-sensitivity of pig-carotid-actomyosin ATPase in relation to phosphorylation of the regulatory light chain.

Ca2+-dependent phosphorylation of the 20000-Mr regulatory light chain was found to be a necessary condition for the Ca2+-sensitivity of the Mg2+-dependent ATPase activity and superprecipitation of pig carotid actomyosin. Actin-myosin interaction independent of phosphorylation and Ca2+ (ATPase activity and superprecipitation) were demonstrated in aged actomyosin preparations and in preparations from which the regulatory light chains were removed by papain digestion.