Characterization of the anion transport channel protein in human erythrocytes. Induced circular dichroism of inhibitors bound to the anion transport channel

Abstract

The induced circular dichroism (CD) of erythrocyte ghosts with anion-transport inhibitors has been studied. A ghost-EITC (eosin 5-isothiocyanate) system shows an induced CD spectrum at the wavelength region corresponding to the absorption bands of EITC. Also a ghost-EMI (eosin 5-maleimide) system shows induced CD, but has bands of opposite sign to the EITC system. From the change of the CD intensity, the number of EITC molecules bound to one erythrocyte was estimated to be about 1.4·10 6, being close to the number of band 3 copies per ghost. The CD spectra of EITC and EMI systems show that a configurational structure of the moiety anchoring the EMI molecule is the reverse to that of EITC. The preferred conformation of bound EITC may be twisted in a right-handed sense. From the signs of the induced CD bands in ghost-stilbene disulfonate systems, the chirality of twisted stilbene derivatives seems to be a left-handed sense, as is the case for the EMI derivative. The CD spectra of EITC in the presence of DIDS (4,4′-diisothiocyanostilbene-2,2′-disulfonate) shows that the binding site of EITC may not be identical with that of DIDS. The results observed in this study reflect the ternary arrangement of the functional amino groups in anion recognition sites.