Enthalpy of nucleotides binding to myosin.

The enthalpies of binding adenosine 5'-diphosphate (ADP) and 5'-adenylyl imidodiphosphate [AMP-P(NH)P] to rabbit skeletal myosin have been measured in Pipes and Tris buffers at pH 7.8 and 15 degrees C. For ADP the enthalpy of binding was exothermic, whereas the enthalpy of binding AMP-P(NH)P, a nonhydrolyzable ATP analogue, was small and endothermic. For the reaction of ATP and myosin, the development of enthalpy was resolved into two phases: a fast endothermic phase, which is the summation of binding and hydrolysis, and a slow exothermic phase, which is associated with product-release steps. These results are discussed in terms of their implications for energy transduction.