Radiation-inactivation analysis of the Na+/bile acid co-transport system from rabbit ileum.
The functional-unit molecular size of the Na+/bile acid cotransport system and the apparent target size of the bile-acid-binding proteins in brush-border membrane vesicles from rabbit ileum were determined by radiation inactivation with high-energy electrons. The size of the functional transporting unit for Na(+)-dependent taurocholate uptake was determined to 451 +/- 35 kDa, whereas an apparent molecular mass of 434 +/- 39 kDa was measured for the Na(+)-dependent D-glucose transport system. Proteins of 93 kDa and 14 kDa were identified as putative protein components of the ileal Na+/bile acid cotransporter in the rabbit ileum, whereas a protein of 87 kDa may be involved in passive intestinal bile acid uptake. Photoaffinity labelling with 3- and 7-azi-derivatives of taurocholate revealed a target size of 229 +/- 10 kDa for the 93 kDa protein, and 132 +/- 23 kDa for the 14 kDa protein. These findings indicate that the ileal Na+/bile acid co-transport system is in its functional state a protein complex composed of several subunits. The functional molecular sizes for Na(+)-dependent transport activity and the bile-acid-binding proteins suggest that the Na+/bile acid co-transporter from rabbit ileum is a homotetramer (AB)4 composed of four AB subunits, where A represents the integral 93 kDa and B the peripheral 14 kDa brush-border membrane protein.
Kramer
W
W
Hoechst Aktiengesellschaft, Frankfurt am Main, Federal Republic of Germany.
Girbig
F
F
Gutjahr
U
U
Kowalewski
S
S
D000345:Affinity Labels; D000818:Animals; D001692:Biological Transport; D018826:CD13 Antigens / Q000737:chemistry; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects*; D005947:Glucose / Q000378:metabolism; D007082:Ileum / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008871:Microvilli / Q000378:metabolism; D008970:Molecular Weight; D029363:Organic Anion Transporters, Sodium-Dependent; D010777:Photochemistry; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology; D013393:Sucrase / Q000737:chemistry; D027981:Symporters; D013656:Taurocholic Acid / Q000378:metabolism
D000345:Affinity Labels; D002352:Carrier Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; C071908:sodium-bile acid cotransporter; D013656:Taurocholic Acid; D012964:Sodium; D013393:Sucrase; D018826:CD13 Antigens; D005947:Glucose