Calcium Sensitivity of Foot Muscle Myosin from Clam (Meretrix lusoria)

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Abstract
It was found that Mg-ATPase of clam foot myosin is strongly activated by calcium or strontium ions and is as sensitive to those divalent cations as the Mg-ATPase and superprecipitation of rabbit skeletal acto-clam foot myosin are. It was also found that desensitization and resensitization of clam foot myosin result in the loss of superprecipitation activity with acto-desensitized myosin and in its recovery with acto-resensitized myosin, respectively. However, the ATPase activity in the absence of calcium ions rises with acto-desensitized myosin and falls again with acto-resensitized myosin. It is thus proposed that the primary role of the EDTA-light chain component in calcium regulation is to inhibit myosin-ATPase rather than to inhibit the actin-myosin interaction.

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