| Research Abstract |
NA0344, a novel derivative of antibiotics, inhibited phosphorylation of 20,000 Mr myosin light chain (LC) of smooth muscle native actomyosin containing both phosphotase and calmodulin/myosin LC kinas (MLCK) activity (IC_<50> = 6.2 x 10^<-6> g/ml). The inhibitory effect is attributable to the direct inhibition of MLCK.
NA0344 also inhibited actin-myosin-ATP interaction of the native actomyosin with IC_<50> = 3.7 x 10^<-7> and 3.8 x 10^<-7> g/ml as monitored by superprecipitation and ATPase activity, respectively.
Thoretically, myosin whose phosphorylation is partially inhibited by NA0344 comprises from unphosphorylated myosin, heterodimer myosin isoform with an unphosphorylated LC and a phosphorylated LC, and homodimer myosin isoform with both LC phosphorylated. We have developed the analytical electrophoresis separating these isomers and found that IC_<50> for the homodimer in native actomyosin was at the level of 10^<-7> g/ml. If we assume that only the homodimer is active in actin-myosin-ATP interaction, inhibition of the interaction can be explatined by that of myosin phosphorylation with MLCK.
Recently, okadaic acid has been reported to enhance actin-myosin-ATP interaction. The effect is interpreted to be mediated by inhibiting phosphatase activity resulting in the enhancement of phosphorylation. We succeeded in preparing the native actomyosin which does not contain phosphatase activity. With this preparation, the enhancing effect was observed, indicating that okadaic acid enhances the interaction directly through myosins.
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