Studies on ligand binding properties of Z-fraction from rat liver cytosol using 1-anilino-8-naphthalenesulfonate.

Abstract

Spectrofluorometric studies using 1-anilino-8-naphthalenesulfonate (ANS) reveal that Z-fraction from rat liver has far the more hydrophobic binding sites than the other cytoplasmic binding fractions X and Y. Diagnostically important organic anions, such a sulfobromophthalein (BSP) and rose bengal (RB), displace ANS from Z-fraction by quenching the fluorescence of ANS and Z-fraction mixture without the change of quantum yield and emission maximum. The binding constants of these dyes to Z-fraction are determined by the competitive studies with ANS, and are coincident with those from other methods. Since the spectrophotometric technique reveals that the number of RB binding sites on Z-fraction is about twice as large as that of ANS binding sites, ANS and RB do not have necessarily the identical binding sites, though they must have-partly common ones. The major binding force between organic anions and Z-fraction is supposed to be hydrophobic considering that the binding constant of Z-fraction for ANS is only about 1/8 of that of bovine serum albumin (BSA) of which site is both hydrophobic and cationic. This property of site accounts for the lower affinity for BSP of Z-fraction extracted from CC11 chronically intoxicated rats, which was made clear previously.