<p>A number of enzymes that catalyze the transfer of a phosphoryl group from phosphoenolpyruvate (PEP) via a phospho-histidine intermediate have been shown to be structurally related [<cite idref="PUB00005010"/>, <cite idref="PUB00001868"/>, <cite idref="PUB00000317"/>, <cite idref="PUB00017924"/>]. These enzymes are: </p><ul><li>Pyruvate,orthophosphate dikinase (<db_xref db="EC" dbkey="2.7.9.1"/>) (PPDK). PPDK catalyzes the reversible phosphorylation of pyruvate and phosphate by ATP to PEP and diphosphate. In plants PPDK function in the direction of the formation of PEP, which is the primary acceptor of carbon dioxide in C4 and crassulacean acid metabolism plants. In some bacteria, such as Bacteroides symbiosus, PPDK functions in the direction of ATP synthesis. </li><li> Phosphoenolpyruvate synthase (<db_xref db="EC" dbkey="2.7.9.2"/>) (pyruvate,water dikinase). This enzyme catalyzes the reversible phosphorylation of pyruvate by ATP to form PEP, AMP and phosphate, an essential step in gluconeogenesis when pyruvate and lactate are used as a carbon source. </li><li> Phosphoenolpyruvate-protein phosphatase (<db_xref db="EC" dbkey="2.7.3.9"/>). This is the first enzyme of the phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS), a major carbohydrate transport system in bacteria. The PTS catalyzes the phosphorylation of incoming sugar substrates concomitant with their translocation across the cell membrane. The general mechanism of the PTS is the following: a phosphoryl group from PEP is transferred to enzyme-I (EI) of PTS which in turn transfers it to a phosphoryl carrier protein (HPr). Phospho-HPr then transfers the phosphoryl group to a sugar-specific permease. </li></ul><p>The entry signature pattern represents a conserved region in the C-terminal part of the PEP-utilizing enzymes. The biological significance of this region is not yet known. </p> PEP-utilising enzyme, conserved site