MOAT4, a novel multispecific organic-anion transporter for glucuronides and mercapturates in mouse L1210 cells and human erythrocytes.
Glucuronides and mercapturates were examined as possible high-affinity substrates for a low-affinity ATP-dependent transport system for 2,4-dinitrophenyl S-glutathione (DNP-SG) in mouse L1210 cells. Initial inhibitor studies with inside-out vesicles revealed that the low-affinity transport of [3H]DNP-SG (Km 450 microM) exhibits a high sensitivity to N-acetyl 2,4-dinitrophenyl cysteine (NAc-DNP-Cys) (Ki 5.0 microM) and alpha-naphthyl beta-D-glucuronide (naphthyl glucuronide) (Ki 8.5 microM). Direct transport measurements showed the presence of ATP-dependent uptake activities for NAc-DNP-[35S]Cys and naphthyl [14C] glucuronide, and Km values for half-maximal transport were comparable to the Ki values of these compounds for inhibition of [3H]DNP-SG transport. Transport of [3H]DNP-SG, NAc-DNP-[35S]Cys and naphthyl [14C]glucuronide each showed the same sensitivity to various anions and anion conjugates. Inhibition was competitive and was most potent for bilirubin ditaurate, indoprofen, 4-biphenylacetic acid, 4-acridine 4 beta-D-glucuronide, N-acetyl leukotriene E4, 17 beta-oestradiol 3 beta-D-glucuronide and taurolithocholate 3-sulphate. Inside-out vesicles from human erythrocytes contain a comparable ATP-dependent transport system. These results show that NAc-DNP-Cys and naphthyl glucuronide are high-affinity substrates for a single system identified previously as a low-affinity transporter of DNP-SG. Substrate and inhibitor studies identify this system as a novel multispecific organic-anion transport system (MOAT4) that accommodates glucuronides and mercapturates and is distinct from other MOAT transporters. Human erythrocytes contain an additional ATP-dependent system for NAc-DNP-Cys (Km 33 microM) that does not transport monoglucuronides.
Saxena
M
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Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92307, USA.
Henderson
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GB
D000111:Acetylcysteine / Q000378:metabolism*; D000818:Animals; D027321:Anion Transport Proteins; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism*; D005965:Glucuronates / Q000378:metabolism*; D005978:Glutathione / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D017136:Ion Transport; D007700:Kinetics; D007939:Leukemia L1210 / Q000378:metabolism* / Q000473:pathology; D051379:Mice
D027321:Anion Transport Proteins; D002352:Carrier Proteins; D005965:Glucuronates; C030190:S-(2,4-dinitrophenyl)glutathione; D005978:Glutathione; D000111:Acetylcysteine