Organic acid transporter polypeptides

Immunohistochemical study ND not determined GLUT1 facilitative glucose transporter MCT1 monocarboxylate transporter CRT creatine transporter LAT1 L-type amino acid transporter TAUT taurine transporter ENT equilibrative nucleoside transporter Oatp organic anion-transporting polypeptide PAH p-aminohippuric acid RUI retinal uptake index TR-iBRB rat retinal capillary endothelial cells. 

OATP/oatp Organic anion transporting polypeptide (protein / nucleic acid)... 

Figure 2.1 Hepatocyte basolateral bile acid transporters. Protein-bound bile acids returning in portal blood are taken up by the hepatocyte via the sodium taurocholate co-transporting polypeptide (NTCP) and organic-anion-transporting polypeptide (OATP). In cholestasis bile acids may be returned to blood by the multi-drug-resistance-associated protein 3 (MRP3).

Jung D, Podvinec M, Meyer UA, et al. Human organic anion transporting polypeptide 8 promoter is transactivated by the farnesoid X receptor/bile acid receptor. Gastroenterology 2002 122 1954-1966. 

HagenbuchB, Lubbert H, StiegerB, Meier PJ (1990) Expression of the hepatocyte Na+/bile acid cotransporter in xenopus laevis oocytes. J Biol Chem 265 5357-5360 Kullak-Ublick GA, Hagenbuch B, Stieger B (1995) Molecular and functional characterization of an organic anion transporting polypeptide cloned from human liver. Gastroenterology 109 1274-1282... 

The drug uptake (SLC) family of transporter is the largest superfamily of transporters. This family includes 31 transporters from organic anion transporter polypeptides (OATPs), organic anion transporters (OATs), organic cation transporters (OCTs), peptide cotransporters (PEPTs), and sodium-bile acid cotransporter classes. Only OATP, OAT, OCT, and PEPT are primarily involved with the transport of drugs/xenobiotics. 

Jung, D., Podvinec, M., Meyer, U. A., Mangelsdorf, D. J., Fried, M., Meier, P. J., and Kullak-Ublick, G. A. (2002) Human organic anion transporting polypeptide 8 promoter is transactivated by the farnesoid X receptor/bile acid receptor. Gastroenterology 122, 1954-1966. 

Fig. 5. Transport of bile acids in the enterohepatic circulation. The left and right sides of the figure depict a liver and intestinal cell, respectively. Bile acids (BA) are made from unesterified cholesterol (UC) in the liver. The movement of bile acids in the enterohepatic circulation is vectorial. The major transporters thought to be responsible for the entry and exit of bile acids in liver and intestinal cells are sodium/taurocholate cotransporting polypeptide (ntcp SLClOAl), bile salt export pump (bsep ABCBll), apical/sodium bile acid cotransporter (asbt SLC10A2), and organic solute transporters a/p, (Osta/P).

Apart from being the building blocks of proteins, many amino acids are indispensable for certain vital functions or have specific functions of their own. They can function as neurotransmitters, as precursors for neurotransmitters and other important metabolites, including crucial oligo- and polypeptides, as a stimulus for hormonal release, and in inter-organ nitrogen transport and nitrogen excretion. Consequently, manipulation of free amino acid levels by dietary or topical supplementation may support and modulate these specific functions. 

The electron transport protein, cytochrome c, found in the mitochondria of all eukaryotic organisms, provides the best-studied example of homology. The polypeptide chain of cytochrome c from most species contains slightly more than 100 amino acids and has a molecular weight of about 12.5 kD. Amino acid sequencing of cytochrome c from more than 40 different species has revealed that there are 28 positions in the polypeptide chain where the same amino acid residues are always found (Figure 5.27). These invariant residues apparently serve roles crucial to the biological function of this protein, and thus substitutions of other amino acids at these positions cannot be tolerated. 

Mammalian COX (the illustration shows the enzyme from bovine heart) is a dimer that has two identical subunits with masses of 204 kDa each. Only one subunit is shown in detail here the other is indicated by gray lines. Each subunit consists of 13 different polypeptides, which all span the inner mitochondrial membrane. Only polypeptides I (light blue) and II (dark blue) and the linked cofactors are involved in electron transport. The other chains, which are differently expressed in the different organs, probably have regulatory functions. The two heme groups, heme a (orange) and heme ai (red) are bound in polypeptide 1. The copper center Cua consists of two copper ions (green), which are coordinated by amino acid residues in polypeptide II. The second copper (Cub) is located in polypeptide I near heme... 

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