Intramolecular dioxygenases

Dioxygen reduction (oxidase activity) and activation for incorporation into organic substrates are catalysed by a number of mononuclear non-haem iron enzymes. We will first consider the intramolecular dioxygenases, in which both atoms of oxygen are introduced into the substrate, then the monoxygenases (in which we choose to include the pterin-dependent hydroxylases), the large family of a-hetoacid-dependent enzymes, and finally isopenicillin N-synthase. 

Among the mononuclear non-haem iron enzymes catalysing hydroxylation reactions (Table 2.3) we can distinguish between intramolecular dioxygenases and external mononoxygenases. The former can be divided into those which are pterin-dependent and those which use a-ketoacids such as a-keto glutarate as obligatory... 

The term intramolecular dioxygenases may be used for the dioxygenases catalyzing the reaction shown in Eq. (8), and intermolecular dioxygenases for those catalyzing the reactions shown in Eqs. (9) and (10), respectively. 

Dioxygenases can incorporate the two oxygen atoms into separate substrates (intermolecular dioxygenases) or into a single molecule (intramolecular dioxygenases) [16a]. 

Dioxygenases introduce both atoms of an oxygen molecule into substrates. In most instances the two oxygen atoms react with one substrate molecule (intramolecular dioxygenases) ... 

It is thus the intramolecular analogue to the a-ketoacid dioxygenase reaction discussed in the preceding section. The same requirements for ferrous ion and a reducing agent are observed. 

The high activity of M(L )2 + L (L = crown-ethers or ammonium quaternary salts) as catalysts of the ethylbenzene oxidation into a-phenylethylhydroperoxide is connected with the formation active primary complexes (M(II)(L )2), (L ), and homo poly nuclear hetero ligand complexes M(II) (L )y(L ) L j, ( A (Ni), B (Fe)) (formed through dioxygenase-like mechanisms). The stability of A ( B ) to the L dioxygenation seems to be due to the intramolecular and intermolecular H-bonding interactions. 

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