Abstract
Treatment of F‐actin pellet with 1 M MgCl2 results in a high concentration of monomer actin in solution [Biró, E. N. A. and Venyaminov, S. Yu. (1979) Acta Biochim. Biophys. Acad. Sci. Hung. 14, 31–42]. The physico‐chemical properties of this actin solution were studied by the spin‐labelling method and were compared with the normal actin solutions. The electron paramagnetic resonance (EPR) spectra produced the following results. The rotational correlation time for monomer actin at low ionic strenght, which was calculated by the extrapolation procedure, increased from 16 ns to 26 ns in the presence of 1 M MgCl2. The polymerization of actin is accompanied by a change in the polarity of the environment of the label (increasing hydrophobicity). When heavy meromyosin (HMM) was added to monomer actin at high ionic strengh, the EPR data provided evidence that HMM induced the polymerization of the MgCl2‐depolymerized actin.
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