Figure 11.

Working model of E. coli HemW. Heme from heme biosynthesis is transferred via the bacterioferritin Bfr (gray) as a carrier to the heme chaperone HemW (orange). Dimerized, the [4Fe–4S] cluster–containing HemW localizes to the membrane where it interacts with its target protein, NarI (yellow), a subunit of the respiratory nitrate reductase NarGHI. After heme incorporation into apo-NarI, the holo-NarGHI catalyzes the reduction of nitrate to nitrite. PPO is protoporphyrinogen IX oxidase; FC (HemH) is ferrochelatase.