Distribution of 3 alpha-hydroxysteroid dehydrogenase (bile acid binder) in rat small intestine: comparison with glutathione S-transferase subunits.

We identified and quantitated the Y' bile acid binder, i.e., 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD), in rat small intestinal mucosa, and compared its longitudinal distribution with that of glutathione S-transferases (GST). The enzyme activity of 3 alpha-HSD in intestinal mucosa was approximately one-third of that in liver, and it had similar activity in the proximal, middle, and distal portions of the intestine. Immunoreactive protein corresponding to hepatic bile acid binder was detected in all segments of rat small intestine mucosal cytosol by Western blot analysis. There was no significant difference in the concentration of bile acid binder, assayed by enzyme-linked immunosorbent assay (ELISA), between the proximal and the distal intestine, this being 2.93 +/- 0.03 and 3.29 +/- 0.95 nmol/g tissue, respectively (mean +/- SD of four animals). On the other hand, the concentration of GST 1-1 showed sharp longitudinal decline and that of GST 3-4 was negligible in the small intestine, as we previously reported, indicating that bile acid binder was a prominent cytosol binding protein in the distal intestine. These results suggested the possible role of bile acid binder in the intracellular transport of bile acids in the ileum.