Binding of progesterone to a-acid glycoprotein

F ure ] 3SaJ . Absorption and first derivative specua of 13 pM ai-acid glycoprotein in buf aipH7. 

We notice that r decreases upon binding of progesterone to a i-acid glycoprotein. Thus, tyrosines microenvironment is more hydrophobic in presence of progesterone. Therefore, binding site of progesterone contains at least one tyrosine. 

Fluorescence is the emission by a fluorophore of a photon from the lowest excited state Si to the ground state So. Emission of the photon occurs with a precise energy E and thus it will be observed at a precise wavelength (A.em). Emission occurs from a population of n excited fluorophores, therefore it will occur with an intensity I 

Transition from different vibrational levels will occur simultaneously with the emission, with energies lower than that of the emitted photon, generating a fluorescence spectrum with a maximum corresponding to the emission transition. 

Emission lifetime is within the pico-to the nanosecond range. Thus, emission is a very fast process. Therefore, in order to observe fluorescence emission, the fluorophore should be excited continuously. 

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