DILUTION BEYOND A TRANSITION CONCENTRATION AND THE ENHANCED FILAMENTSFORMATION OF ACTIN IN THE LOW IONIC-STRENGTH BUFFER

Actin in the low ionic strength buffer solution G (0.1 mM ATP, 0.1 mM CaCl2, 2 mM Tris-Cl (pH 8.0), 5 mM 2-mercaptoethanol and 1 mM NaN3) wa s diluted to the concentration below 10 mu g/ml at 7 degrees C. Viscom etry showed associations of actin monomers and increasing the extent o f dilution, maximally about 75% of actin were precipitated. Act-in fil aments were observed by electron microscope in the diluted solution. C a2+ plays a role in the filaments' formation. It seems that a phase tr ansition like change in the actin states arose at this concentration r ange.