The intrinsic fluorescence of globular actin: Peculiarities in the location of tryptophan residues

The contribution of individual Trp residues to alpha-actin fluorescence was evaluated by means of an analysis of their microenvironment, which was don e on the basis of PIR-International protein sequence database information. The contribution of Trp(79) and Trp(86) was shown to be low due to an effec tive nonradiating energy transfer according to the inductive resonance mech anism between the Trp residues and the fluorescence quenching of Trp(86) by S-gamma of Cys(10), an efficient fluorescence quencher. The intrinsic fluo rescence of actin was found to be determined mainly by Trp(340) and Trp(356 ), which are internal, inaccessible to solvent, and have a high density mic roenvironment formed mainly by nonpolar groups of protein. It is possible t hat the side chain conformation of Trp(340) (t-isomer; chi(1) 190 degrees, chi(2) 89 degrees), aromatic rings of Tyr and Phe residues, and Pro residue s in the microenvironment of Trp(340) and Trp(356) substantially contribute to the short-wavelength fluorescence spectrum of actin.