Figure 1. An overview of anaerobic hydrogen metabolism and nitrate respiration metabolism in E. coli.

The metabolism of pyruvate under anaerobic conditions is shown in the upper portion of the Figure. The cellular locations of the three main [NiFe]-hydrogenases, the three molybdoselenium formate dehydrogenases and the principle nitrate reductase are shown, as are the transport systems for nickel and molybdate. The metal ion requirement and regulation with respect to the global regulator FNR are also indicated by arrows.