Fluorescence Time‐Resolved Spectroscopy and Fluorescence Anisotropy Decay of the Staphylococcus aureus Endonuclease

Abstract
The intrinsic fluorescence of Staphylococcus aureus endonuclease has been studied by the time‐resolved spectroscopy method. The tyrosine emission, with a decay time of 1.8 ns, is separated from the tryptophan emission with a decay time of 5.5 ns.The binding of an inhibitor, thymidine 3′,5′‐bisphosphate (pdTp), decreases the intensity of the tyrosine spectrum.The molecular correlation time determined by the anisotropy decay measurement of the tryptophanyl residue is 8.9 ns. This value corresponds to a strongly hydrated molecule.The fixation of pdTp does not change this correlation time, showing that no gross structural modifications are induced by the inhibitor.