A spectroscopic study of the hemin-human-alpha-fetoprotein system

The binding of hemin to human alpha-fetoprotein has been estimated by means of fluorescence and spectrophotometric titration. Spectrophotometric titration discloses one strong binding site for hemin with an association constant of 1.5 X 10(7) M-1. The binding causes a shift of the absorption maximum to a higher wavelength and a rise in the molar absorption coefficient. Fluorescence reveals that the binding of hemin to human AFP quenches the protein fluorescence, which changes in character from a tryptophan type to a tyrosine type. As postulated by our results, the binding of hemin to human AFP is similar to the binding of hemin to HSA.