低塩濃度下におけるスルメイカ筋肉ミオシンとアクチオンの相互作用

概要

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We found previously that squid myosin B was markedly different from squid myosin in the KCl concentration dependence of Ca-ATPase activity, i.e. the maximal activity of squid myosin B was obtained at 0.2-0.3M KCl and a rapid decrease in the activity occurred as the KCl concentration decreased. In contrast, squid myosin showed a maximum activity at 0.1M KCl. A further study was conducted and the results obtained were as follows: 1) At KCl concentrations lower than 0.2M, the Ca-ATPase activity of squid myosin was remarkably decreased by addition of F-actin. 2) A maximum turbidity of acto-squid myosin was also obtained at 0.2M KCl. 3) A concomitant activation of Mg-ATPase of myosin occurred when the Ca-ATPase activity of squid myosin was inhibited by F-actin. 4) The reduced activity of Ca-ATPase of acto-squid myosin in the low KCl medium was fully recovered upon addition of 1M urea. 5) The Ca-ATPase activity of squid HMM was no longer inhibited by F-actin. It is therefore concluded that the inhibition of Ca-ATPase activity of squid myosin by F-actin occurred only when a thick filament of myosin was applied to ATPase assay.