PT  - JOURNAL ARTICLE
AU  - Liu, Xiaoxiao
AU  - Huang, Jiujiu
AU  - Sun, Yongxue
AU  - Zhan, Kai
AU  - Zhang, Zheren
AU  - Hong, Mei
TI  - Identification of Multiple Binding Sites for Substrate Transport in Bovine Organic Anion Transporting Polypeptide 1a2
AID  - 10.1124/dmd.112.047910
DP  - 2013 Mar 01
TA  - Drug Metabolism and Disposition
PG  - 602--607
VI  - 41
IP  - 3
4099  - http://dmd.aspetjournals.org/content/41/3/602.short
4100  - http://dmd.aspetjournals.org/content/41/3/602.full
SO  - Drug Metab Dispos2013 Mar 01; 41
AB  - Organic anion transporting polypeptides (OATP) have been extensively recognized as key determinants of absorption, distribution, metabolism, and excretion of various drugs because of their broad substrate specificity, wide tissue distribution, and the involvement of drug-drug interaction. As the first cloned human OATP, OATP1A2 has been found to transport a wide spectrum of endogenous and exogenous compounds. Bovine Oapt1a2 shared high homology with the human transporter and is considered as its functional ortholog. In the present study, we expressed bovine Oatp1a2 in human embryonic kidney 293 cells and found that, unlike human OATP1A2, the transport of estrone-3-sulfate (E-3-S) exhibited biphasic saturation kinetics. The Km values are 0.25 ± 0.08 and 46.6 ± 18.5 µM, and Vmax values were 24.5 ±4.4 and 375 ± 142 pmol/mg protein/min for high- and low-affinity sites, respectively, suggesting the presence of multiple binding sites. Further study on other Oatp1a2 substrates showed that the high affinity component for E-3-S is responsible for the interaction with taurocholate, bromsulphthalein, and rifampicin and is sensitive to proton concentration change, whereas the low affinity binding site is only involved in the binding of the antitumor drug methotrexate and had no response to change of pH.