Drug binding sites on chicken albumin: a comparison to human albumin

Mammalian albumins have two main structurally selective ligand binding sites. Site I binds drugs such as azapropazone, phenylbutazone and warfarin; whereas benzodiazepines, some dansyl amino acids, such as dansylsarcosine, and short chain fatty acids like octanoic acid interact with site II. However, it is not known if non-mammalian albumins have similar binding loci. In this study, drug binding sites on chicken albumin were investigated using site selective fluorescent probes (warfarin and dansylsarcosine) and p-nitrophenyl acetate (NPA); the hydrolysis of which is selectively inhibited by site II ligands. Azapropazone and phenylbutazone decreased the binding of warfarin and dansylsarcosine to a similar extent. Diazepam and octanoic acid also inhibited binding of the two fluorescent probes in a non-selective manner. However, the fluorescence intensity of the warfarin-chicken albumin complex decreased when the pH was increased from 6.0-9.0; but by contrast, the fluorescence of bound dansylsarcosine remained unchanged. Furthermore, the hydrolysis of NPA was selectively inhibited by dansylsarcosine, diazepam and octanoic acid (ligands selective for site II on mammalian albumins), but not by site I selective ligands such as azapropazone and warfarin. Overall, the results suggest that chicken albumin, like mammalian albumins, has discrete binding sites for warfarin and dansylsarcosine.