The bacterial phosphoenolpyruvate: sugar phosphotransferase system

The bacterial phosphotransferase system participates in diverse physiological phenomena; its best characterized function is in the group translocation of sugars that are substrates of the system. Such sugars are phosphorylated as they are translocated across the cell membrane. Isolation of different proteins of the phosphotransferase system and reconstitution of the complex shows that in the net transfer of the phosphoryl group from phosphoenolpyruvate to a given sugar the phosphoryl group is sequentially transferred from one protein to another. In all cases so far studied, with one important exception, the phosphoryl group is linked to the proteins through a nitrogen atom in the imidazole ring of a histidyl residue. In the exceptional protein, the phosphoryl group is linked to a carboxy group. An additional function of the phosphotransferase system is to regulate the uptake of sugars that cannot be phosphorylated.