Environment of the rotating unit

The Weber method provides parameters characteristic of the environment of the rotating unit such as the limiting anisotropy and the thermal coefficient to resistance to a rotation. Also, the method permits to separate the motion of different classes of fluorophore. 

Perrin plot and red-edge excitation spectra experiments performed on Trp residues of sialylated and asialylated ai-acid glycoprotein have shown that in both proteins the intrinsic fluorophore displays local motions and are surrounded by a flexible environment. However, the above two mentioned methods yield information on the mean residual motion and can in no way give an indication on the dynamics of each class of Trp residues. In fact, the exposed tryptophan residue should be expected to rotate much more freely than the hydrophobic residues. In order to study the dynamics behavior of each class of Ti p residues, steady-state measurements of emission anisotropy at different temperatures (-45 to + 30°C) can be carried out. This method (the Weber s method) known also as the Y-plot, allows deriving parameters characteristic of the environment of the rotating unit, such as the thermal coefficient of the frictional resistance to the rotation of the fluorophore. 

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