Identity of hepatic membrane transport systems for bile salts, phalloidin, and antamanide by photoaffinity labeling.

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Abstract
Phalloidin, a bicyclic heptapeptide, and antamanide, a monocyclic decapeptide from the poisonous mushroom Amanita phalloides, interact with bile-salt-binding polypeptides of the [rat] hepatocyte membrane; this was demonstrated by photoaffinity labeling using the photolabile bile salt derivative 7,7,-azo-3.alpha.,12.alpha.-dihydroxy-5.beta.-cholan-24-oic acid, either unconjugated or taurine conjugated. With the photolabile derivatives of phalloidin, N.sbd.d{4-[(1-azi-2,2,2-trifluoroethyl)benzoyl]-.beta.-alanyl}-.delta.-aminophalloin and of antamanide, {N.epsilon.-[4-(1-azi-2,2,2-trifluoroethyl)benzoyl]lys6}-antamanide, the same membrane polypeptides with apparent MW of 54,000 and 48,000 were labeled as with the photolabile derivatives of unconjugated and conjugated bile salts. The presence of bile salts decreased markedly the extent of labeling of these phalloidin-and antamanide-binding polypeptides. Hepatic uptake systems for bile salts, phallotoxins and the cycloamanide antamanide are apparently identical, thus explaining the organotropism of phallotoxins.