title: Specificity and topology of the Escherichia coli xanthosine permease, a representative of the NHS subfamily of the major facilitator superfamily.
abstract: The specificity of XapB permease was compared with that of the known nucleoside transporters NupG and NupC. XapB-mediated xanthosine uptake is abolished by 2,4-dinitrophenol and exhibits saturation kinetics with an apparent K(m) of 136 microM. A 12-transmembrane-segment model was confirmed by translational fusions to alkaline phosphatase and the alpha fragment of beta-galactosidase.
authors.affiliation: Department of Biological Chemistry, Institute of Molecular Biology, University of Copenhagen, 1307 Copenhagen K, Denmark.
authors.forename: M H
authors.initials: MH
authors.lastname: Nørholm
authors.forename: G
authors.initials: G
authors.lastname: Dandanell
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D004926:Escherichia coli / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012263:Ribonucleosides / Q000378:metabolism*; D012984:Software; D013379:Substrate Specificity; D014970:Xanthines
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C088081:NupC protein, Bacteria; C490231:NupC protein, E coli; C098551:NupG protein, E coli; D012263:Ribonucleosides; D014970:Xanthines; C095872:XapB protein, E coli; C005893:xanthosine