The effect of elimination of the gastrointestinal flora on the accumulation of methylmercuric chloride by the rat.

CM-Sephadex chromatography (phosphate buffer, l o r n , pH7.4) resolved the lithocholicacid-binding mixture obtained fromDEAE-Sephadex into two fractions, both able to bind lithocholic acid and both having glutathione S-transferase activity. Agarose and polyacrylamide-gel electrophoresis of the fractions obtained from CM-Sephadex chromatography demonstrated the presence of only a single protein-containing band in each fraction. These fractions were further investigated for glutathione S-transferase activity by measuring the conjugation of ethacrynic acid [2,3-dichloro-4-(2-ethylacryloy1)phenoxyacetic acid] with glutathione. Both fractions had this activity, suggesting that one of them is the anion-binding proteinligandin (Habigetal., 1974). The physiological relevance of these findings is not clear. The value of the dissociation constant for binding of lithocholic acid to hepatic supernatants suggests a transport function. Ligandin can bind many different anions which are transported into bile by the liver (Levi et al., 1969). Phylogenetic and clinical studies have led to the proposal that ligandin is involved in the hepatic transport of bromosulphophthalein and bilirubin. It seems unlikely, however, that ligandin is involved in the transport of bile acids as well as bilirubin and bromosulphophthalein, since studies have suggested that bile acid transport is mediated by a mechanism different from the other anions.