Enzymes catechol dioxygenases

An enzymatic pathway for indole degradation was found in A. niger, inducible by the substrate within a 5-h period during growth. Among the enzymes found, anthranilate hydroxylase, N-formylanthranilate deformylase, 2,3-dihydroxybenzoate decarboxylase, and catechol dioxygenase were isolated, and their activities were demonstrated in a cell-free system [342],... 

Bugg, T. D. H., and Lin, G., Solving the Riddle of the Intradiol and Extradiol Catechol Dioxygenases How Do Enzymes Control Hydroperoxide Rearrangements. J. Chem.Soc. Chem. Commun., 2001. pp. 941-952. 

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.)...

Other non-heme enzymes that use dioxygen are 4-methoxy-benzoate O-demethylase, extradiol catechol dioxygenases, the oxidoreductase isopenicillin N synthase, and a-keto acid-dependent enzymes (28). Moreover, the BH4-dependent glyceryl-ether monooxygenase (GEM) also appears to be dependent on nonheme iron for catalysis (see also Section I.E). 

These studies are part of a rare family of examples of the chemoselec-tive oxidation of catechols (150). The identification of the catalyst and the interception of the catalyst-dioxygen adduct are of particular relevance when the chemistry of catechol dioxygenase and tyrosinase enzymes is concerned. 

These two enzymes are also colorless and contain the ferrous form of iron90,91,94. The properties of catechol dioxygenases are summarized in Table 3. 

The nonheme iron-containing dioxygenases other than the catechol dioxygenases mentioned above are listed in Table 6. For the details of these enzymes, the readers are referred to the original references of individual enzymes or the review articles14,81. ... 

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... 

A spectacular example of stability enhancement through immobilization has been reported for the enzyme catechol-2,3-dioxygenase.27 This enzyme, isolated from the thermophilic bacterium Bacillus stearothermophilus, catalyzes the conversion of catechol to 2-hydroxymuconic semialdehyde (which can be monitored by absorbance at 375 nm). The soluble enzyme exhibits maximal activity at 50 °C, but following immobilization on glyoxyl agarose beads with a borohydride reduction step, the optimum reaction temperature shifted to 70 °C. At a total protein concentration of 0.010 mg/mL and a temperature of 55 °C, the half-life of the soluble enzyme was 0.08 h, while the enzyme-modified beads had a half-life of 68 h. This represents a 750-fold enhancement of stability that has been attributed to the prevention of subunit dissociation upon immobilization. 

The dioxygenation of unsaturated a-diols (catechol and benzoin. Table 6-2) by the O2/Fe l(DPAH)2 system parallels that of the catechol dioxygenase enzymes, which are nonheme iron proteins. -l Hence, the reactive intermediate (1, Scheme 6-1) of the Feh(DPAH)2/O2 reaction may be a useful model and mimic for the activated complex of dioxygenase enzymes. ... 

The intradiol cleaving catechol dioxygenases are bacterial iron-containing enzymes that serve as a component of nature s mechanism for degrading aromatic compounds in the environment. These enzymes, represented by catechol 1,2-dioxygenase (CTD) and protocatechuate(3,4-dihydroxybenzoate) 3,4-dioxygenase (PCD), catalyze the reaction... 

Catechol dioxygenases are nonheme iron enzymes which catalyze the oxidative cleavage of catechols. [Fe(Cat)(Tp )(Hpz )] [Cat = catecholate = C6H4O2, 3,5- Bu2, C6H2O2, C6CI4O2) have been prepared and their reactivity toward O2 investigated.94... 

Dioxygenase enzymes are known that contain heme iron, nonheme iron, copper, or manganese.The substrates whose oxygenations are catalyzed by these enzymes are very diverse, as are the metal-binding sites so probably several, possibly unrelated, mechanisms operate in these different systems. For many of these enzymes, there is not yet much detailed mechanistic information. However, some of the intradiol catechol dioxygenases isolated from bacterial sources have been studied in great detail, and both structural and mechanistic information is available. These are the systems that will be described here. 

---