Essential component of the OST-alpha/OST-beta complex, a heterotetramer that acts as the intestinal basolateral transporter responsible for bile acid export from enterocytes into portal blood (PubMed:16317684, PubMed:41606314, PubMed:41606328). The OST-alpha/OST- beta complex efficiently transports the major species of bile acids (taurocholate) (PubMed:16317684, PubMed:41606314, PubMed:41606328). Taurine conjugates are transported more efficiently across the basolateral membrane than glycine-conjugated bile acids (By similarity). In the complex, SLC51B/OST-beta promotes the transmembrane translocation of bile acids (PubMed:41606314, PubMed:41606328). Can also transport steroids such as estrone 3-sulfate and dehydroepiandrosterone 3-sulfate, therefore playing a role in the enterohepatic circulation of sterols (PubMed:16317684). Able to transport eicosanoids such as prostaglandin E2 (By similarity). {ECO:0000250|UniProtKB:Q80WK2, ECO:0000250|UniProtKB:Q90YM4, ECO:0000269|PubMed:16317684, ECO:0000269|PubMed:41606314, ECO:0000269|PubMed:41606328}. This is the function of SLC51B (SLC51 subunit beta, ENSG00000186198).