Abstract
The Z-fraction in rat liver cytoplasm, defined first by Levi et al. [J. clin. Invest.48, 2156 (1969)] as an organic anion binding fraction of small molecular weight (10,000–14,000) was further purified by the method of ion-exchange chromatography. The purification was characterized by the use of 1-anilino-8-naphthalenesulfonate (ANS) in sensitively detecting the organic anion binding protein in the Z-fraction. The Z-fraction was found to contain three protein fractions having fairly high binding activities for ANS and sulfobromophthalein (BSP). Among these fractions, the D 2-fraction, which eluted earlier on a DEAE-Sephadex column, had the highest binding affinity for these anions. This D 2-fraction was further purified by CM-Sephadex chromatography. The ANS binding protein, thus purified. was similar in physico-chemical properties to the aminoazodye-binding protein of S 20.w 1.6s (Form III) reported by Ketterer et al. [Biochem. J.155. 511 (1976)]. The binding affinities for both ANS and BSP were little influenced by the purification. By the fluorescence method, about 30 per cent of the protein in the Z-fraction was found to be this binding protein. The binding stoichiometries for the high affinity sites were 0.7 for ANS and 0.4 for BSP.
Published Version
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