The mechanism of proton-coupled lactose transport in E. coli is an example of:
In Escherichia coli, lactose accumulation during lactose operon induction exemplifies secondary active transport powered by proton motive force, not direct ATP hydrolysis or simple diffusion. LacY permease co-transports one H+ and one lactose molecule; downhill H+ movement through transporter allows uphill lactose concentration. Gradient is sustained by primary H+ extrusion by respiratory chain complexes pumping protons outward, generating proton electrochemical gradient consisting of pH and membrane potential. When respiration is active, periplasmic proton binds outward-open LacY, increases a
Ref: Kaback, Biochim Biophys Acta 2015, LacY proton coupling; Alberts, Chapter 11 secondary transport.
