Circular dichroic examination of the interaction of some planar acidic drugs with tryptophan-modified human serum albumin.

The single tryptophan region in human serum albumin was investigated for its involvement in binding planar hydrophobic and acidic drug molecules. The lone tryptophan was alkylated with a selective and specific agent, 2-hydroxy-5 nitrobenzyl bromide. The subsequent interaction of four drug molecules with tryptophan modified, and normal albumin was examined by circular dichroism (CD). In all cases the CD signal of tryptophan modified albumin was perturbed at low drug concentrations. The predominantly alpha-helical structure of the albumin remained intact. It is suggested that the primary binding site of these four acidic planar drugs does involve the tryptophan region.