Iron oxygenases triad

The 2-His-l-Carboxylate Facial Triad in Non-Heme Iron Oxygenases 101... 

The number of known or presumed mononuclear, non-heme iron oxygenases and related enzymes continues to grow. This is due to intensive biochemical research and especially based on sequence data derived from genome research projects i.14). For several of these enzymes structural data are available by now from protein crystallography (12-14). In many of the iron oxygenases the iron is facially bound by two histidines and one carboxylate donor, either glutamic acid or aspartic acid. Thus, the term 2-His-l-carboxylate facial triad has been introduced by L. Que Jr. for this motif (19). 

Rieske oxygenases are part of a superfamily of enzymes that share a characteristic structure consisting of an oxygenase component (a mononuclear non-heme iron(II) high spin center containing a 2-His-l-carboxylate facial triad motif in the active site) [31-33]. Besides, the active site contains a reductase component (an Fe2-S2 Rieske center) that delivers electrons from NAD(P)H to the oxygenase center [34]. 

High-resolution ENDOR of iron-NO complexes has proven ideal for resolving questions about the relative orientations of exogenous iron ligands in facial triad oxygenases. Because this volume has a chapter devoted to recent ENDOR studies (see Chapter 3), only a brief account of one example, in which an Fe-NO complex... 

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