Relation between energy transfer and static quenching

Relation between energy transfer and static quenching 

The binding parameters (stoichiometry and association constant) are usually determined from the intensity decrease of the tryptophan residues. However, when energy transfer occurs, errors in the determination of the association constant can be observed. 

The following example describing hemin binding to human a i-acid glycoprotein illustrates the latter two paragraphs. 

TNS binds to a i-acid glycoprotein with a dissociation constant of 60 pM and a stoichiometry of 1 1. The nature of the binding site is hydrophobic although contacts with a polar environment (solvent) do exist (Albani et al. 1995). 

Binding studies are performed between ai-acid glycoprotein and hemin, a co-factor that binds to the hydrophobic pocket of hemoproteins. If a i-acid glycoprotein contains a hydrophobic pocket, hemin will bind to this pocket with a well defined stoichiometry. Also, if TNS and hemin bind to the same binding site and if the affinity of hemin to ai-acid glycoprotein is more important than that of TNS, binding of hemin to a protein-TNS complex will remove the TNS from its binding site. 

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