NrfD is an integral transmembrane protein with loops in both the periplasm and the cytoplasm. NrfD is thought to participate in the transfer of electrons, from the quinone pool into the terminal components of the Nrf pathway [1].

1: A seven-gene operon essential for formate-dependent nitrite reduction to ammonia by enteric bacteria. Hussain H, Grove J, Griffiths L, Busby S, Cole J; Mol Microbiol 1994;12:153-163. PMID:8057835