Heme iron structures

The hemerythrin of Golfingia gouldii consists of eight subunits, each of which contains two iron atoms, in a protein with molecular weight 108,000. Spectral and magnetic data point to an oxo-bridged structure around the non-heme iron atom (99). Protein B2 of ribotide reductase of E. coli has some properties in common with hemerythrin presumably a protein corresponding to that of E. coli reduces ribotides in animal tissues, a conclusion based on probes with inhibitors. 

Figure 8.1 Heme (iron protoporphyrin IX) structure. The most frequently observed cleavages in LDMS of the intact species are denoted. Heme elemental composition is C34H32N404Fe monoisotopic molecular mass is 616.176 Da average molecular mass is 616.487 Da.

Hegg, E. L. and L. Que (1997). The 2-His-l-carboxylate facial triad-An emerging structural motif in mononuclear non-heme iron(II) enzymes. Eur. J. Biochem. 250(3) 625-629. 

Emerson, J.P., Farquhar, E.R. and Que, L. Jr. (2007) Structural snapshots along reaction pathways of non-heme iron enzymes. Angewandte Chemie, International Edition, 46, 8553-8556. 

One of the most unusual features of the vitamin B12 structure is that cobalt is bonded directly to carbon. In heme, iron is bonded to five nitrogen atoms, but the sixth position is vacant until oxygen attaches. In vitamin B12, the sixth position is that bonded to the group indicated by R in the structure... 

Peroxidases are heme iron-containing proteins similar in structure to that of cytochromes P450. The major difference is that peroxidases have histidine as the axial ligand instead of cysteine, and there are also other polar amino acids close to the heme iron that help to catalyze the peroxidase function of the enzyme (41). The result is that the peroxidases very rapidly catalyze the reduction of hydroperoxides to alcohols (or water in the case of... 

P450 2C9 crystal structure information also served in docking and molecule dynamics operations to simulate the simultaneous binding of a heteroactivator and a substrate [ 17]. N SAID substrates were thereby positioned nearer to the heme than the heteroactivator. For the latter, limited conformational freedom was discovered because of the reduced active-site volume. The presence of an activator shortened the substrate-heme iron distances leading to an increase in the number of catalytic... 

Cytochrome c can easily be extracted from tissue particles by dilute salt solutions. It was isolated by Keilin and Hartree in 1930 and shown to contain a porphyrin ring structure. In 1933 Zeilen and Reuter established that cytochrome c was a heme (iron-porphyrin) protein. Slightly different forms of cytochrome a were distinguished in yeast and bacteria by Keilin in 1934 and the different properties of cytochrome a and a3 by Tamiya et al. in 1937. The identity of cytochrome 03, the enzyme which activates oxygen with Warburg s atmungsferment, was proposed by Keilin in 1939. Cytochrome a/a3 was renamed cytochrome oxidase by Malcolm Dixon (1939). The oxidation route then offered was ... 

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). 

The coordination sphere around the ferrous iron center is almost octahedral with the heteroscorpionate clamp causing a deviation of 4-6° from the ideal 90° angle. A comparison with very high-resolution protein structures such as IPNS or CAS clearly shows a good correspondence of structure 4b in distances and angles with the active sites of the non-heme iron enz5unes (Table I). 

This emphasizes that iron(II) complexes bearing more bulky bis(pyrazol-l-yl)acetate ligands should be good structural models to mimic mononuclear non-heme iron dependent enzymes. 

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