Figure 3.

Representation of the X-ray crystallographic structure of the F₄₂₀-reducing hydrogenase from Methanothermobacter marburgensis, the only structurally characterized member of Group 3 [NiFe] hydrogenases. Prepared using Pymol,⁷ PDB code 4OMF. The active site and iron sulfur clusters are shown as spheres in elemental colors, and the flavin adenine dinucleotide (FAD) cofactor is shown in red sticks. Considerable variation in subunit composition, structure, and physiological function exists in the Group 3 enzymes.