Ai-Acid glycoprotein - progesterone

The steady-state emission spectrum of the crystals obtained with unpolarized excitation light (Fig. 8.52A) does not overlap the emission spectrum of ai- acid glycoprotein - progesterone complex obtained in solution (Fig. 8.52B), but overlaps the spectrum of hydrophobic Trp residues of the protein (Fig. 8. 53). Thus, the fluorescence observed for the crystal is characteristic of Trp residues embedded in the protein matrix. Therefore, the two Trp residues surrounded by a hydrophobic environment have the same microenvironments in crystal and in solution. 

Figure 8.51. Fluorescence excitation spectrum of a crystal of ai- acid glycoprotein -progesterone complex. A.em 335 nm. The spectrum was recorded by excitation with unpolarized light. Source Albani, J. R. 1998, Journal of Fluorescence, 8, 213-224. Authorization of reprint accorded by Kluwer Academic Publishers.

Albani, J.R. (2006) Progesterone binding to the tryptophan residues of human ai-acid glycoprotein. 

Canguly, M. and Westphal, U. (1968, Steroid-protein interactions. XVII. Influence of solvent environment on interaction between human ai-acid glycoprotein and progesterone. Journal of... 

Progesterone binds to a i-acid glycoprotein on a hydrophobic region of a pocket present in the protein. Figure 1.35 shows the absorption spectrum of 13 pM ai-acid glycoprotein in buffer at pH 7, its first and second derivative spectra... 

Table 1.6. Position and absorption of the peaks and troughs of the second derivative spectra in the 270-300 nm region of 13 pM ai-acid glycoprotein in absence and presence of 50 pM progesterone.

Table 8.8 shows that binding of progesterone on ai-acid glycoprotein induces a shift in the emission maximum of both Trp-residues. Therefore, a modification of the local structure occurs near the Trp-residues upon binding of progesterone to the protein. 

Figure 8.42. Titration of 42 juM calcofluor bound to 8 juM ai-acid glycoprotein with progesterone. Xex 310 nm. Spectrum 1 is obtained in absence of progesterone while spectrum 14 is obtained in presence of 62 pM progesterone.

Figure 8.43. (a) Fluorescence intensity variation of 42 pM of calcofluor bound to 8 pM of ai-acid glycoprotein as a function of progesterone. = 310 nm and X< m = 440 nm. (b) Fluorescence intensity titration of free calcofluor in presence of increasing concentrations of progesterone. Source De Ceukeleire, M. and Albani, J. R. 2002, Carbohydrate Research 337, 1405-1410. 

Figure 8.47. Raman spectrum of native form ai- add g tx)pcoteiiL (Bottom) Raman difference spectrum of native tti- acid glycoprotein minus ai acid glycoprotein wMi tiound progesterone. Positions of amino acids with aromatic side chains, wiA respect to their environment or surface of the protein, have been also determined. Cuitosey from Vbdimir Kopecky Jr., ROd er Enrich, Katefina Hofbauoova and Vladimir Baumnic...

Albani, J. R, 2002, Interaction between carbohydrate residues of ai- acid glycoprotein (orosomucoid) and progesterone. A fluorescence study. Carbohydrate Research 337, 1405-1410. 

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