Albumin fluorescence emission spectra

Although a number of proteins of interest (human serum albumin, for example) contain a single Trp, most contain two or more. Thus the spectrum observed is the sum of all active Trp fluors, making it difficult to deduce the local environment of each fluor. Nevertheless, the UV fluorescence emission spectrum is useful in deducing orientation and/or conformation changes upon adsorption. 

Figure 8.6 clearly indicates that in the presence of free tryptophan in solution, there is no binding of TNS on the amino acid. However, in the presence of bovine serum albumin, TNS shows a fluorescence emission spectrum, indicating that TNS is bound to the protein. 

Figure 3.29 shows file fluorescence emission spectra of lO pM Quin-2 at different concentrations of calcium (0 to 40 pM) in the absence (A) and in the presence (B) ol 15.3 pM human serum albumin. From the data of figure 3.29, the authors generate steady-state emisaon spectra of the protein (Fig. 3.30a), Quin-2 (Fig. 3.30b), file Quin-2-calcium complex (Fig. 3.30c) and the Quin-2 - protein complex (Fig. 3.30d). One can notice that Quin-2 fluorescence emission spectrum in presence ofhuman serum albumin is blue slufted compared to Quin-2 flee in solution. The Quin-2-calcium complex is however red-shifted.

Figure 8.5 shows fluorescence emission spectra of TNS and ANS bound to serum albumin. The two fluorophores do not show the same maximum, although the two fluorophores bind to hydrophobic domains of the protein. This result can be explained mainly by the differences in the structure of the two fluorophores. Also, one could explain the difference in the emission peaks could be due to the higher sensitivity of TNS to hydrophobicity. This interpretation is based on the fact that the peak of TNS emission spectrum is shifted to short wavelengths compared to that of ANS... 

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