Inverse interaction between tropomyosin and phosphorylated myosin in the presence or absence of caldesmon

In the present study, co-sedimentation assay, intrinsic fluorescence intensity measurement, and Mg^2＋-ATPase ac-tivity analysis were carried out to investigate the direct effect of tropomyosin （TM） on unphosphorylated myosin （UM） or phosphorylated myosin （PM） in the presence or absence of ealdesmon （CAD）. Results showed that TM sig- nificantly decreased the sedimentation, intrinsic fluores-cence intensity, and the Mge~-ATPase activity of PM, but not UM. In the presence of CaD, TM also significantly decreased these parameters irrespective of myosin phos- phorylation, suggesting that the interaction between TM and CaD abolished the effects of TM on PM or UM and that there was an inverse interaction between TM and PM, characterized by the decreased PM sedimentation and intrinsic fluorescence intensity.