A hydrophobicity on skeletal muscle actin molecule modulated by nucleotide binding at a second site

A hydrophobic region was detected on skeletal muscle actin molecule by change of fluorescence of a hydrophobic probe, 8-anilino-1-naphthalene-sulfonate (ANS). In previous papers (Hozumi, T. (1988) Biochem. Int. 17, 171-178; Hozumi, T. (1988) J. Biochem. (Tokyo) 104, 285-288) evidences for a second nucleotide binding site on a actin molecule were reported and it was shown that nucleotide interaction at the site induces conformational changes in actin molecule. The character of non-polar region of actin molecule was altered by the binding of nucleotide at a new site of actin molecule, the fluorescence of the ANS-actin being greatly decreased, and its emission maximum undergoing a red-shift. These results show that nucleotide binding at a second site on actin changes its conformation, and the conformational change induces changes in the native surface hydrophobicity on actin molecule.