title: Vitamin B12 transport in Escherichia coli: energy coupling between membranes.
abstract: Cells of Escherichia coli possess high-affinity active transport systems of vitamin B12 and iron-siderophore complexes. Specific outer-membrane proteins carry out the energy-dependent transport across the outer membrane, in conjunction with the TonB coupling protein. Mutagenesis experiments have identified a conserved region near the amino-terminus of the outer-membrane transporters that is necessary for energy-coupled transport. The ability of extragenic suppressor mutations in tonB to correct the transport defect indicates that TonB couples the proton-motive force to the outer-membrane proteins by direct contact.
authors.affiliation: Department of Microbiology, School of Medicine, University of Virginia, Charlottesville 22908.
authors.forename: R J
authors.initials: RJ
authors.lastname: Kadner
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism; D004735:Energy Transfer; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D014805:Vitamin B 12 / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli; D014805:Vitamin B 12; D002118:Calcium