The relevance of functional amino acids for taurocholate transport by the sodium-dependent taurocholate cotrans-porting polypeptide Ntcp was determined by site-directed mutagenesis. cRNAfrom28 single-pointsmutants of the rat liver Ntcp clone was expressed in Xenopus laevisoocytes. Mutations were generated in five conserved negatively chargedaminoacids (aspartates andglutamates)whichwere present in nine members of the SBAT-family, in two non-conserved negatively charged amino acids, in all eight Ntcp-cysteines, and in two threonines from a protein kinase C consensus region of theNtcpC-terminus. .
