Tryptophan emission from myosin subfragment 1: acrylamide and nucleotide effect monitored by decay-associated spectra

The intrinsic emission due to the tryptophan residues of the heavy chain of myosin subfragment 1 can be divided into three classes, on the basis of spectra associated with lifetimes of 0.72, 4.5, and 8.8 ns. The percentage contribution of each component to the total emission is 9%, 45%, and 46%, respectively. Low concentrations of acrylamide quench the long component with a quenching constant of 14.9 +/- 2.9 M-1, while the intermediate and short components are unaffected. Upon addition of ATP the total intensity increases by 17%. The bulk of this increase is in the intermediate lifetime component. Quenching by acrylamide in the presence of ATP again quenches only the long lifetime component, indicating that the tryptophan residues affected by ATP binding are not accessible to the solvent.