1E2A

Enzyme II lactose belongs to a class of lactose/cellubiose-specific family of enzymes II which act as sugar specific permeases. The enzyme is involved in the phosphotransferase system (PTS), a mechanism responsible for the specific binding, transmembrane transport and phosphorylation of a carbohydrate substrate. The PTS is a major carbohydrate transport system in bacteria and catalyses the phosphorylation of incoming sugar substrates, coupled with translocation across the cell membrane. The function of PTS enzymes makes this system a link between the uptake and metabolism of sugars.

The complete PTS acts as follows: a phosphoryl group from phosphoenolpyruvate (PEP) is transferred via a signal transduction pathway, to enzyme I (EI) which in turn transfers it to a phosphoryl carrier, the histidine protein (HPr). Phospho-HPr (the substrate for this entry) then transfers the phosphoryl group to a sugar-specific permease, a membrane-bound complex known as enzyme 2 (EII), which transports the sugar to the cell. EII consists of at least three structurally distinct domains IIA, IIB and IIC [PMID:1537788]. These can either be fused together in a single polypeptide chain or exist as two or three interactive chains, formerly called enzymes II (EII) and III (EIII).