Sulfate conjugated organic anions

Another sinusoidal transporter catalyzes Na+-independent uptake of organic anions and is instrumental for biliary clearance of glucuronidated and sulfated steroids, the diagnostic chemical bromosulfophthalein (BSP) and possibly bilirubin. Canalicular transport of glucuronidate and GSH conjugates is coupled to ATP... 

Figure 28.3. Transport of bile acids and other constituents across the hepatocyte. The Na+ dependent bile salt (taurocholate) transporter (BA-) is shown on the sinusoidal membrane that utihzes the Na+ gradient maintained by the NAK pump, shown here on the lateral aspect of the plasmalemma. Bile salt transcellular transport involves microtubules, which then dehver substrate to the canahcular bile salt transporter (1). Bilary excretion of GSH, gluc-uronate (GluA), and sulfate conjugates of compounds such as 17P-estradiol (E2), bilirubin, and bromosulfothalein (BSP) is catalyzed by the multispecific organic anion transporter (MOAT 2). Both 1 and 2 are members of the ABC family of ATP-dependent transporters that also includes P-glycoprotein (3), another canalicular transporter catalyzing excretion of hpophihc compounds such as the chemotherapeutic drug, daunorubicin.

Shin, H.J., Anzai, N., Enomoto, A., He, X., Kim do, K., Endou, H. and Kanai, Y. (2007) Novel liver-specific organic anion transporter OAT7 that operates the exchange of sulfate conjugates for short chain fatty acid butyrate. Hepatology (Baltimore, Md.), 45, 1046—1055. 

Glutathione, glucuronide and sulfate conjugates. Hydrophilic with organic anion. Substrates overlap between MRPl, MRP2, and MRP3, such as calcein, LTC4, methotrexate, and vinblastine. 

The chemical is removed before it can properly reach the cytoplasm or important organelles. The substrates for this transporter are structurally diverse but tend to be organic, weakly basic (cationic), or uncharged hydrophobic or amphipathic substances. Thus, the chemical diffuses into the cell and is then pumped out. Substrates include anions conjugated with glutathione (GSH), glucuronic acid, and sulfate. 

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