The phosphoenolpyruvate-dependent sugar phosphotransferase system (sugar PTS), a major carbohydrate active transport system, catalyzes the phosphorylation of incoming sugar substrates concomitantly with their translocation across the cell membrane. The enzyme II LacEF PTS system is involved in lactose transport. lactose(out) + N(pros)-phospho-L-histidyl-[protein] = L-histidyl-[protein] + lactose 6-phosphate(in) By lactose. The operon consists of lacABCDFEGX. A second transcript of only lacF and lacE is also lactose-induced. The EIIC type-3 domain forms the PTS system translocation channel and contains the specific substrate-binding site. The PTS EIIB type-3 domain is phosphorylated by phospho-EIIA on a cysteinyl residue. Then, it transfers the phosphoryl group to the sugar substrate concomitantly with the sugar uptake processed by the PTS EIIC type-3 domain.