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 complex composed of PtsG and Crr is involved in glucose transport (PubMed:6754734, PubMed:6292227). It can also phosphorylate mannose, methyl alpha-glucoside and 2-deoxy-glucose (PubMed:6292227). The non-phosphorylated EIII-Glc is an inhibitor for uptake of certain sugars such as maltose, melibiose, lactose, and glycerol. Phosphorylated EIII-Glc, however, may be an activator for adenylate cyclase (PubMed:789369). Binds 1 zinc ion per glycerol kinase EIIA-Glc dimer. The zinc ion is important for dimerization. Heterodimer with glycerol kinase (glpk). The EIIA domain is phosphorylated by phospho-HPr on a histidyl residue. Then, it transfers the phosphoryl group to the EIIB domain. In mutants defective in enzyme I and histidine-containing phosphate carrier protein (HPr), cells lacking this gene are able to grow on the non-PTS compounds such as glycerol, maltose, melibiose, mannose 6-phosphate, and alpha-glycerol phosphate. Two forms of III-Glc (called IIIGlc Slow and IIIGlc Fast) are present in living cells. IIIGlc Fast, derived from IIIGlc Slow by cleavage of the seven NH2-terminal amino acids, is present only in trace quantities and has slight activity (only 2-3% of phospho-IIIGlc Slow) in the phosphorylation of sugar. Both forms accept phosphate from phosphoenolpyruvate via Enzyme I and HPr, however only IIIGlc Slow participates in the phosphorylation of glucose or methyl alpha-D-glucoside. IIIGlc Fast may play a role in the regulation of non-PTS sugar transport systems.