Extradiol cleaving

Figure 13.21 Mononuclear non-haem iron enzymes from each of the five families in structures which are poised for attack by 02. (a) The extradiol-cleaving catechol dioxygenase, 2,3-dihydroxy-biphenyl 1,2-dioxygenase (b) the Rieske dioxygenase, naphthalene 1,2-dioxygenase (c) isopenicillin N-synthase (d) the ot-ketoglutarate dependent enzyme clavaminate synthase and (e) the pterin-dependent phenylalanine hydroxylase. (From Koehntop et al., 2005. With kind permission of Springer Science and Business Media.)...

Table 3 compares some key properties of the enzyme-substrate complexes of the intradiol and extradiol cleaving dioxygenases. A mechanism for extradiol cleavage must account for the differing metal requirements of the two classes of enzymes and their distinct regiospecificities. A key difference is the reactivity of the ES complexes toward NO. Whereas the ES complexes of extradiol enzymes readily react with NO to form ES—NO adducts, those of intradiol enzymes do not react with NO unless the Fe(III) center is reduced prior to exposure to NO [167], Thus the Fe(II) center in the extradiol cleaving enzymes appears... 

The extradiol-cleaving enzymes are more challenging to study than their intradiol-cleaving counterparts because of the lability of the Fe centers and the difficulty of probing such sites by spectroscopy. Sequence comparisons classify the enzymes in this category into three subclasses, " but crystallographic data for representative proteins of each subclass show a common active site with the metal center bound to two His residues and an Asp or a Glu residue, which... 

Figure 9 Proposed mechanism for the extradiol-cleaving catechol dioxygenases...

To date the few structurally characterized biomimetic extradiol-cleaving systems are all five-coordinate iron(III)... 

Little is known about the nature of the iron active sites in these enzymes. With the application of modern spectroscopic methods to the catechol enzymes, we are beginning to get a glimpse of the iron coordination during the catalytic process. Much remains to be done before a well-defined picture emerges. Similar studies on the other systems are still to be undertaken. We have limited the scope of this discussion to these three classes of enzymes because most progress has been achieved in these systems. Still to be studied are the extradiol cleaving catechol dioxygenases and the... 

Iron-containing extradiol-cleaving dioxygenases are well known (see Iron Proteins with Mononuclear Active Site. ... 

Figure 8 Schematic views of extradiol-cleaving dioxygenases.

Manganese(II)-Dependent Extradiol-Cleaving Catechol Dioxygenases... 

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