Solubilization of bilirubin by cholate micelles. Spectroscopic and gel permeation studies

Abstract

The interactions of bilirubin with bile salts were studied by fluorescence, CD, and 1H NMR methods. Enhancement of bilirubin fluorescence and induction of optical activity in bilirubin in the presence of cholate has been obsd. Fluorescence enhancement is pronounced above the crit. micelle concn., whereas induced CD bands are detectable even in the premicellar region. Dehydrocholate and deoxycholate did not increase fluorescence, but did induce CD bands for bilirubin. Gel-permeation chromatog. on Sephadex G-50 yielded a single bilirubin-cholate species at alk. pH, whereas 2 species were obtained at neutral pH. 1H NMR and CD spectral characterizations of these complexes are reported. A 4:1 cholate-bilirubin mixt. was analyzed by difference NOE spectroscopy. Observation of strong, neg. NOE, both intermol. and intramol., suggests that specific Me groups on bilirubin and cholate are proximal in the mixed micelle