Fig. 1

Scheme of the processes occurring in the chemostat during nitrite utilization in E. coli cells. (1) – nitrite inflow and outflow at steady-state flow rate; (2) – reduction of extracellular nitrite to ammonium mediated by periplasmic NrfA reductase; (3),(4) – import of the extracellular nitrite into the cell and its export from the cell into the chemostat mediated by the NirC transporter; (5) – intracellular nitrite utilization mediated by cytoplasmic NirB reductase; (6) – NrfA and NrfB proteins synthesis from the nrf operon mRNA and NirB, NirC and NirD synthesis from the nir operon mRNA; (7) – transport of the Nrf reductase A and B subunits from the cytoplasm to the periplasm and back; (8) – formation of the NirC transporter active pentameric form; (9) – formation of the NirB reductase active heteromeric form; (10) – formation of the Nrf active heterotetrameric form; (11) – degradation of proteins and their complexes (degradation process is illustrated in the figure only for two monomers)