Functional significance of interaction of H-FABP with sulfated and nonsulfated taurine-conjugated bile salts in rat liver.
To identify the cytosolic proteins of rat hepatocytes involved in transcellular transport of sulfated and taurine-conjugated bile salts in comparison with only taurine-conjugated bile salts, photoaffinity labeling studies were performed with [3H]-7,7-ASLCT (7,7-azi-3 alpha-sulfatolithocholyl[2'-3H(N)]taurine), [3H]-7,7-ACT ((7,7-azi-3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oyl)- 2'-[2'-3H(N)]aminoethanesulfonate), and [3H]-7,7-ALCT (7,7-azilithocholyl[2'-3H(N)]taurine) using isolated hepatocytes and intact liver tissue. Photoaffinity labeling of isolated hepatocytes with [3H]-7,7-ASLCT on the one hand and with [3H]-7,7-ACT and [3H]-7,7-ALCT on the other resulted in a different labeling pattern of cytosolic polypeptides, without a relevant incorporation of radioactivity into subunits of glutathione transferases. This suggests that glutathione transferases play no role in the transport of dianionic or of monoanionic bile salts. With [3H]-7,7-ACT and [3H]-7,7-ALCT a moderate incorporation of radioactivity was found in polypeptides with apparent M(r)s of 33,000, 38,000, and 54,000, whereas with [3H]-7,7-ASLCT, a polypeptide with an apparent M(r) of 14,000, identified as H-FABP, was markedly and almost exclusively labeled. Photoaffinity labeling of specimens of intact liver tissue resulted in a labeling pattern of cytosolic polypeptides comparable to that obtained from photolabeled isolated hepatocytes. All results suggest that transcellular transport of dianionic sulfated as well as taurine-conjugated bile salts and of monoanionic taurine-conjugated bile salts follows different pathways. In intracellular transport of taurine-conjugated bile salts, several cytosolic polypeptides may have a function, whereas, in transport of taurine-conjugated 3 alpha-sulfato bile salts, only H-FABP appears to be involved.
Dietrich
A
A
Institut für Organische Chemie und Biochemie, Universität Freiburg, Germany.
Dieminger
W
W
Fuchte
K
K
Stoll
G H
GH
Schlitz
E
E
Gerok
W
W
Kurz
G
G
D000345:Affinity Labels; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D007525:Isoelectric Focusing; D008099:Liver / Q000378:metabolism*; D008297:Male; D018996:Myelin P2 Protein / Q000378:metabolism*; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D011233:Precipitin Tests; D051381:Rats; D017208:Rats, Wistar; D012995:Solubility; D013347:Subcellular Fractions / Q000737:chemistry / Q000378:metabolism; D013463:Sulfuric Acid Esters / Q000378:metabolism*; D013654:Taurine / Q000378:metabolism*; D013658:Taurolithocholic Acid / Q000031:analogs & derivatives / Q000378:metabolism
D000345:Affinity Labels; D001647:Bile Acids and Salts; D002352:Carrier Proteins; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D018996:Myelin P2 Protein; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D013463:Sulfuric Acid Esters; C066776:taurolithocholic acid 3-sulfate; D013654:Taurine; D013658:Taurolithocholic Acid