Encyclopedia of Biophysics

Living Edition
| Editors: Gordon Roberts, Anthony Watts, European Biophysical Societies

H+/Lactose Membrane Transport Protein, LacY

  • Lan GuanEmail author
  • H. Ronald Kaback
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-35943-9_665-1



LacY ( aka Lac permease) is the product of the lacY gene, the second structural gene in the lac operon, which encodes a single polypeptide that is solely responsible for all the translocation reactions of β-galactoside transport in E. coli. LacY (TCDB 2.A.1.5.1) belongs to the oligosaccharide/H + symporter subfamily of the major facilitator superfamily (MFS). LacY is selective for disaccharides containing a d-galactopyranosyl ring, as well as d-galactose, with no affinity for d-glucopyranosides or d-glucose. The native substrate is lactose, which is a disaccharide derived from the condensation of galactose and glucose at a β-1 → 4 glycosidic linkage. The systematic name is β-d-galactopyranosyl-(1 → 4)-d-glucose (Fig. 1). LacY catalyzes reversible translocations of one cargo sugar with one proton (H +), and the coupled translocation between H +and the sugar in the same direction is obligatory. The reaction can be described by the...
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Copyright information

© European Biophysical Societies' Association (EBSA) 2018

Authors and Affiliations

  1. 1.Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein ResearchTexas Tech University Health Sciences CenterLubbockUSA
  2. 2.Departments of Physiology and Microbiology, Immunology & Molecular Genetics, Molecular Biology InstituteUniversity of California, Los AngelesLos AngelesUSA

Section editors and affiliations

  • Peter J. F. Henderson
    • 1
  1. 1.Astbury Centre for Structural Molecular Biology, Institute of Membrane and Systems BiologyUniversity of LeedsLeedsUK