The binding of 8-anilino-1-naphthalene sulfonate (ANS) to fish myosin and the effect of salts on the thermal transitions of fish myosin-ANS complex

Myosin prepared from tilapia (Serotherodon aureus) was complexed with 8-anilino-1-naphthalene sulfonate (ANS) and continuously heated at 1 degree C/min. A large increase in fluorescence was observed with a transition temperature of 34 degrees C. The effect of several salts on the transition temperature was tested. A plot based on the equation of E. E. Schrier and E. B. Schrier (1967) J. Phys. Chem. 71, 1851-1860] gave a value of less than or equal to 500 cal/mol-deg for the change in enthalpy per residue due to exposure to solvent. The ratio of hydrophobic group to amide group exposure to solvent was intermediate compared with the ratio of RNase and gelatin. Fluorescence titrations yielded one high affinity site with a Kb of 2 X 10(6) M-1 and at least 200 low affinity sites with an average value of 1 X 10(5) M-1. The parameters did not change significantly with temperature. We propose that the increase in ANS fluorescence reflects changes in conformation of myosin as monitored by these low affinity sites, resulting in an increase in surface hydrophobicity and representing a small enthalpic change in the conformation of the myosin molecule. As a consequence, the change in conformation accelerates polymerization of myosin oligomers.