May be involved in drug clearance in the placenta. In Xenopus laevis oocytes, in a sodium-independent manner. Syncytiotrophoblast in placenta. Expressed predominantly in testis, also found in placenta and to a lesser extent in thymus and small intestine; abundantly expressed in tumor-derived cell lines (PubMed:16006562). Ubiquitously expressed (PubMed:12819961). May be involved in the development and/or progression of nosopharyngeal carcinoma. The polymorphism 'Glu58Gly' (described in PubMed:12819961) is in fact an error, the G to A change described representing a synonymous mutation that does not induce any amino acid change in Gly-32. Extended N-terminus.