The identification of tryptophan residues responsible for ATP-induced increase in intrinsic fluorescence of myosin subfragment 1

ATP binding to myosin subfragment 1 (S1) induces an increase in tryptophan fluorescence. Chymotryptic rabbit skeletal S1 has 5 tryptophan residues(Trp 113, 131,440, 510 and 595), and therefore the identification of tryptophan residues perturbed by ATP is quite complex. To solve this problem we resolv ed the: complex fluorescence spectra into log-normal and decay-associated c omponents, and carried out the structural analysis of the microenvironment of each tryptophan in S1. The decomposition of fluorescence spectra of S1 a nd SI-ATP complex revealed 3 components with maxima at ca. 318, 331 and 339 -342 nm. The comparison of structural parameters of microenvironment of 5 t ryptophan residues with the same parameters of single-tryptophan-containing proteins with well identified fluorescence properties applying statistical method of cluster analysis, enabled us to assign Trp595 to 318 nm, Trp440 to 331 nm, and Trp113, 131 and 510 to 342 nm spectral components. ATP induc ed an almost equal increase in the intensities of the intermediate (331 nm) and long-wavelength (342 nm) components, and a small decrease in the short component (318 nm). The increase in the intermediate component fluorescenc e most likely results from an immobilization of some quenching groups (Met4 37, Met441 and/or Arg444) in the environment of Trp440. The increase in the intensity and a blue shift of the long component might be associated with conformational changes in the vicinity of Trp510. However, these conclusion s can not be extended directly to the other types of myosins due to the div ersity in the tryptophan content and their microenvironments.