Anomalous binding of MgADP to myosin of skeletal muscle

Binding of adenosine diphosphate to skeletal muscle myosin was studied usin g a range of concentrations from 0 to 2 mM. Up to 0.2 mM adenosine diphosph ate two equivalent and independent nucleotide binding sites were detected, characterized by the single association constant of 5 x 10(4) M-1. At great er adenosine diphosphate concentrations a decreasing binding capacity was n oticed, bound nucleotide being essentially similar to 0.1 mol/mol at a 1-2 mM adenosine diphosphate concentration. We tentatively propose that nucleot ides act indirectly on myosin by promoting the perturbation of the solvent, which is supported by the fact that polyphosphates are known powerful kosm otropes.