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 microM was determined at 20 degrees 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: aflatoxin B1 and phenylbutazone compete for a common high-affinity site on rat albumin; high-affinity binding of aflatoxin B1 and site-II marker ligands takes place independently; 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-transfer studies show that the lone tryptophan residue, Trp-214, is not associated with the aflatoxin B1-binding site.
D016604:Aflatoxin B1; D000348:Aflatoxins / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002793:Cholic Acids / Q000378:metabolism; D008024:Ligands; D010653:Phenylbutazone / Q000378:metabolism; D051381:Rats; D012709:Serum Albumin / Q000378:metabolism*; D012995:Solubility; D013050:Spectrometry, Fluorescence; D014859:Warfarin / Q000378:metabolism
D000348:Aflatoxins; D002793:Cholic Acids; D008024:Ligands; D012709:Serum Albumin; D014859:Warfarin; D016604:Aflatoxin B1; D010653:Phenylbutazone