Component of the phosphoenolpyruvate-dependent nitrogen-metabolic phosphotransferase system (nitrogen-metabolic PTS), that seems to be involved in regulating nitrogen metabolism. Enzyme I-Ntr transfers the phosphoryl group from phosphoenolpyruvate (PEP) to the phosphoryl carrier protein (NPr) (PubMed:10473571). Could function in the transcriptional regulation of sigma-54 dependent operons in conjunction with the NPr (PtsO) and EIIA-Ntr (PtsN) proteins (PubMed:8973315). Enzyme I-Ntr is specific for NPr (PubMed:10473571). L-histidyl-[protein] + phosphoenolpyruvate = N(pros)-phospho-L-histidyl-[protein] + pyruvate Mn(2+) allows activity only at low concentrations. In the presence of low concentrations of Co(2+) or Ni(2+), activity could be measured, but at concentrations above 0.2 mM, strong inhibition is observed. Inhibited by GDP and FAD. Enzyme I-Ntr activity requires high ionic strength. Optimum pH is 8. The EI N-terminal domain contains the HPr binding site, the central domain the pyrophosphate/phosphate carrier histidine, and the C-terminal domain the pyruvate binding site. The GAF domain is an important site of signal perception in prokaryotes and eukaryotes. The reaction takes place in three steps, mediated by a phosphocarrier histidine residue located on the surface of the central domain. The two first partial reactions are catalyzed at an active site located on the N-terminal domain, and the third partial reaction is catalyzed at an active site located on the C-terminal domain. For catalytic turnover, the central domain swivels from the concave surface of the N-terminal domain to that of the C-terminal domain. Belongs to the PEP-utilizing enzyme family.