Encyclopedia of Biophysics

2013 Edition
| Editors: Gordon C. K. Roberts

H+-Lactose Membrane Transport Protein, LacY

  • Lan GuanEmail author
  • H. Ronald Kaback
Reference work entry
DOI: https://doi.org/10.1007/978-3-642-16712-6_665



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 catalyzed by the β-galactoside transport system in E. coli. LacY (TCDB 2.A.1.5.1) belongs to the oligosaccharide/H + symport subfamily of the major facilitator superfamily (MFS), which contains >40,000 members found ubiquitously in all living organisms. LacY is selective for disaccharides containing a d-galactopyranosyl ring, as well as d-galactose, but has no affinity for d-glucopyranosides or d-glucose. LacY catalyzes the vectorial reversible reaction:
$$ {{\text{H}}^{ + }}\left( {\text{out}} \right) + {\text{Lactose}}\left( {\text{out}} \right) \leftrightarrow {\text{Lactose}}\left( {\text{in}} \right) + {{\text{H}}^{ + }}\left( {\text{in}} \right) $$
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Copyright information

© European Biophysical Societies' Association (EBSA) 2013

Authors and Affiliations

  1. 1.Department of Cell Physiology & Molecular Biophysics, Center of 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