Shown here is the crystal structure of leghemoglobin derived from root nodules of yellow lupine (Lupinus luteus L.). Leghemoglobin is a red-colored enzyme active in the environment of N2-fixing nodules; leghemoglobin mediates the high O2 requirements of the N2-fixing bacteroids and the necessity of the O2-limited environment (10-40 nM) for the proper function of nitrogenase in reducing N2 to ammonia.
Highlighting FeaturesShow heme group with associated histidine and dioxygen (O2) Show globin as strands Show globin as strands with heme and dioxygen
Central to the activity of leghemoglobin is the heme group, in which four 5-membered pyrrole rings are joined to form a giant macrocycle in which a central Fe atom resides coordinated with four equatorial nitrogens. The central Fe is further coordinated with an additional N from a nearby histidine residue and, at the other pole, dioxygen (O2). Heme groups are also found in cytochromes, catalases, and peroxidases, as well as hemoglobin, an oxygen-carrying enzyme familiar in the animal kingdom. The tetrapyrrole macrocycle appears also in chlorophyll, with Mg as the central atom.
TN Safonova, AV Teplyakov, GV Obmolova, AN Popov, IP Kuranova, EG Harutyunyan. 1991.Crystal structure of ferric complexes of the yellow lupin leghemoglobin with isoquinoline at 1.8 angstroms resolution (Russian). Bioorg. Khim. 17:1605.