CHARACTERIZATION OF THE AFLATOXIN-B1-BINDING SITE OF RAT ALBUMIN

A fluorescence-enhancement method was used to investigate the non-covalent interaction between aflatoxin B1 and rat albumin. Solvent-induced shifts in the emission spectrum of aflatoxin B1 provided evidence that the aflatoxin B1-binding site of rat albumin is a highly nonpolar environment. A dissociation constant of 20 μM was determined at 20°C. The possibility that aflatoxin B1 binds one of the three major drug sites of albumin was investigated by ligand-displacement experiments. Mechanisms whereby marker ligands displace aflatoxin B1 were further investigated by comparing the experimental binding parameters with those derived theoretically, assuming competitive binding. The results indicate that: (1) aflatoxin B1 and phenylbutazone compete for a common high-affinity site on rat albumin; (2) high-affinity binding of aflatoxin B1 and site-II marker ligands takes place independently; (3) aflatoxin B1 does not compete with either cholate or warfarin for the same high-affinity site, but the simultaneous binding of warfarin or cholate negatively modulates the binding of aflatoxin B1 to albumin. Fluorescence energy-transer studies show that the lone tryptophan residue, Trp-214, is not associated with the aflatoxin B1-binding site. © 1987.