INFLUENCE OF CALTROPIN ON THE CALDESMON INDUCED POLYMERIZATION OF G-ACTIN

The effect of caltropin (CaT) on the caldesmon (CaD)-G-actin interacti on was monitored by viscosity measurements, bioassays measuring the re lease of inorganic phosphate (Pi) following G-actin polymerization and fluorescence studies using acrylodan labelled G-actin. CaD induced po lymerization of G-actin into filaments in the absence of salt was acco mpanied by an increase in relative viscosity. This effect of CaD was e ssentially abolished by CaT in the presence of Ca2+. In bioassays the rate of Pi release was reduced significantly in the presence of Ca2+/C aT. Acrylodan labelled G-actin when excited at 375 nm exhibited an emi ssion maximum at 478 nm. Polymerization of G-actin resulted in shiftin g the emission maximum to 465 nm. When CaD was added to G-actin contai ning Ca2+/CaT, the rate of G-actin polymerization was reduced consider ably, suggesting that CaT interferes in the CaD-G-actin interaction. ( C) 1995 Academic Press, Inc.