Role of Myosin in the Stimulatory Effect of Caldesmon on the Interaction between Actin, Myosin, and ATP1

TL;DRAbstract

We have previously shown that caldesmon at low concentrations stimulates the interaction between actin, myosin, and ATP, while at high concentrations it inhibits the interaction [Ishikawa, R., Okagaki, T., Higashi-Fujime, S., & Kohama, K. (1991) J. Biol. Chem. 266, 21784-21790]. When the effect of caldesmon at low concentrations was monitored by measuring myosin ATPase activity in the absence of actin, the effect was slightly but significantly stimulatory; and at higher concentrations no inhibitory effect was observed. Therefore, we related the stimulatory effect with the myosin-binding property of caldesmon. In the presence of actin, a low concentration of caldesmon was not enough to evince the stimulatory effect: myosin concentration must also be low. This is because the stimulatory effect was obscured when myosin concentration was elevated. Ca(2+)-calmodulin abolished the stimulatory effect of caldesmon. However, the concentration of calmodulin required to abolish the stimulation wa

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