title: Galactoside-dependent proton transport by mutants of the Escherichia coli lactose carrier. Replacement of histidine 322 by tyrosine or phenylalanine.
abstract: Mutations have been introduced into the Escherichia coli lac Y gene by oligonucleotide-directed mutagenesis such that the lactose carrier contains either tyrosine or phenylalanine in place of histidine 322. These mutants did not carry out active accumulation of lactose, melibiose, or methyl-beta-D-galactopyranoside, but facilitated diffusion was still catalyzed. Galactoside-dependent H+ transport, measured with the pH electrode, was retained in both mutants. We conclude that although histidine 322 is important for energy transduction, neither an electronegative atom nor a dissociable proton is essential for proton cotransport with lactose or melibiose.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: S C
authors.initials: SC
authors.lastname: King
authors.forename: T H
authors.initials: TH
authors.lastname: Wilson
mesh_terms: D001692:Biological Transport; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005697:Galactosides / Q000378:metabolism*; D006027:Glycosides / Q000378:metabolism*; D006639:Histidine; D008553:Melibiose / Q000378:metabolism; D008564:Membrane Potentials; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D009154:Mutation; D010649:Phenylalanine; D011522:Protons; D013329:Structure-Activity Relationship; D027981:Symporters; D014443:Tyrosine
chemical_list: D029968:Escherichia coli Proteins; D005697:Galactosides; D006027:Glycosides; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D011522:Protons; D027981:Symporters; D014443:Tyrosine; D010649:Phenylalanine; D006639:Histidine; C021499:lactose permease; D008553:Melibiose