and constitutes the first residue in the heme road.
Residue N393 in the DsrA subunit is aligned to T351 in the DsrB subunit,
but these occupy very different spatial positions (Figure S4). The N393
from the DsrA subunit is part of the C-terminal arm that extends to the
other heterodimer (Figures 1, 5), such that N393A2 inserts itself