Analysis of amino acid residues in the predicted transmembrane pore influencing transport kinetics of the hepatic drug transporter organic anion transporting polypeptide 1B1 (OATP1B1)

We have cloned a murine member of the organic-anion-transporting polypeptide (Oatp) family of membrane-transport proteins from mouse liver. The cloned cDNA insert of 2783 bp with an open reading frame of 2011 bp codes for a 12-transmembrane 670-amino-acid protein with highest amino acid identity with the rat Oatp1. When expressed in Xenopus laevis oocytes, the mouse Oatp exhibited the same substrate specificity as the rat Oatp1. Besides the common Oatp substrates bromosulphophthalein, taurocholate, oestrone 3-sulphate and ouabain, the new mouse Oatp also mediates transport of the Oatp1-specific magnetic-resonance-imaging agent gadoxetate. The Oatp2-specific cardiac glycoside digoxin, however, is not transported. Kinetic analyses performed for taurocholate and oestrone 3-sulphate revealed apparent Km values of 12 μM and 5 μM respectively. Northern-blot analysis demonstrated a predominant expression in the liver with an additional moderate expression in the kidney. Taken together, the amino acid identity, the functional characteristics and the tissue distribution suggest that we have isolated the murine orthologue of the rat Oatp1, and consequently the identified protein will be called Oatp1. Using fluorescence in situ hybridization, the murine Oatp1 gene was mapped to chromosome XA3-A5.

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Studies on tryptophan residues of Abrus agglutinin. Stopped-flow kinetics of modification and fluorescence-quenching studies

Biochemical Journal ◽

10.1042/bj2430079 ◽

1987 ◽

Vol 243 (1) ◽

pp. 79-86 ◽

Cited By ~ 4

Author(s):

S R Patanjali ◽

M J Swamy ◽

A Surolia

Keyword(s):

Amino Acid ◽

Protein A ◽

Stopped Flow ◽

Amino Acid Residues ◽

Acidic Amino Acid ◽

Native Protein ◽

Tryptophan Residues ◽

Stopped Flow Kinetics ◽

Two Phases ◽

Kinetics Of

The presence of two essential tryptophan residues/molecule was implicated in the binding site of Abrus agglutinin [Patanjali, Swamy, Anantharam, Khan & Surolia (1984) Biochem. J. 217, 773-781]. A detailed study of the stopped-flow kinetics of the oxidation of tryptophan residues revealed three classes of tryptophan residues in the native protein. A discrete reorganization of tryptophan residues revealed three classes of tryptophan residues in the native protein. A discrete reorganization of tryptophan residues into two phases was observed upon ligand binding. The heterogeneity of tryptophan exposure was substantiated by quenching studies with acrylamide, succinimide and Cs+. Our study revealed the microenvironment of tryptophan residues to be hydrophobic, and also the presence of acidic amino acid residues in the vicinity of surface-localized tryptophan residues.

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Influence of a proton gradient on the transport kinetics of the H+/amino acid cotransporter PAT1 in Caco-2 cells

European Journal of Pharmaceutics and Biopharmaceutics ◽

10.1016/j.ejpb.2006.01.009 ◽

2006 ◽

Vol 63 (3) ◽

pp. 360-364 ◽

Cited By ~ 8

Author(s):

Linda Metzner ◽

Matthias Brandsch

Keyword(s):

Amino Acid ◽

Transport Kinetics ◽

Proton Gradient ◽

Kinetics Of

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