Fluorescent investigations of binding of phenprocoumon to alpha 1-acid glycoprotein.

The fluorescence of phenprocoumon is greatly enhanced on binding to a single site on alpha 1-acid glycoprotein (alpha 1-AGP). Advantage is taken of this phenomenon to estimate a binding constant for the binding of phenprocoumon to alpha 1-AGP. The fluorescence intensity and binding constant of the phenprocoumon: alpha 1-AGP complex decreased with pH from 6.5 to 8.5, suggesting that phenprocoumon binding to alpha 1-AGP is significantly affected by microenvironmental change in alpha 1-AGP. A variety of drugs, including chlorpromazine and dicumarol, significantly inhibited phenprocoumon binding to alpha 1-AGP. Fatty acids seem to displace phenprocoumon from its binding site on alpha 1-AGP, whereas the addition of neutral salts and sialic acid did not cause the displacement of phenprocoumon. It is concluded that the phenprocoumon binding site is located in the hydrophobic protein structure of alpha 1-AGP.