2.3- Dihydroxybenzoate 2.3-dioxygenase

Mechanistic Aspects of Dihydroxybenzoate Dioxygenases John D. Lipscomb and Allen M. Orville... 

Rhizobia. Taxa belonging to both the genera Rhizobium and Bradyrhizobium are capable of degrading simple aromatic compounds including benzoate (Chen et al. 1984) and 4-hydroxy-benzoate (Parke and Omston 1986 Parke et al. 1991). It has been shown that 4-hydroxyben-zoate hydroxylase is required for the transport of 4-hydroxybenzoate into the cell (Wong et al. 1994). In strains of Rhizobium trifolium, the metabolism of benzoate involves either 3,4-dihydroxybenzoate (protocatechuate) 3,4-dioxygenase (Chen et al. 1984), or catechol... 

FIGURE 3.12 Biodegradation of 3,4-dihydroxybenzoate mediated by (a) 4,5-dioxygenase in Pseudomonas acidovorans and (b) 2,3-dioxygenase in Bacillus macerans. 

The second large group of ring-fission dioxygenases are used for the degradation of ortho-dihy-droxybenzoates including, 2,3-, 3,4-, and 4,5-dihydroxybenzoate. As for simple catechols, hssion may be either intradiol or extradiol, and the choice between them depends on the organism ... 

Heavy-metal cations and oxyanions are generally toxic to bacteria although resistance may be induced by various mechanisms after exposure. Attention is drawn to an unusual example in which AF+ may be significant, since the catechol 1,2-dioxygenase and 3,4-dihydroxybenzoate (protocat-echuate) 3,4-dioxygenase that are involved in the metabolism of benzoate by strains of Rhizobium trifolii are highly sensitive to inhibition by AP (Chen et al. 1985). 

The third alternative for ring fission of 3,4-dihydroxybenzoate is exemplified by Bacillus macerans and B. circulans that use a 2,3-dioxygenase to accomplish this (Figure 8.30b)... 

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],... 

This enzyme [EC 1.14.13.35], also referred to as anthranilate 3-monooxygenase (deaminating) and anthranilate 2,3-dioxygenase (a transferred entry, formerly EC 1.14.12.2), catalyzes the reaction of anthranilate with NADPH and dioxygen to generate 2,3-dihydroxybenzo-... 

Benzoate 1,2-dioxygenase was shown to catalyze the conversion of benzoate to l,2-dihydro-l,2-dihydroxybenzoic acid (DHB) in the presence of NADH and oxygen by Reiner et al.205, 206). Yamaguchi et al.61> have demonstrated that the enzyme system consists of two components (A and B),both of which are required for benzoate 1,2-dioxygenase activity. Component A shows NADH-cytochrome c reductase activity and component B appears to be dioxygenase, thus the following reaction scheme is suggested [Eq. (25)]. 

These enzymes are red in color and contain ferric ion as the sole cofactor. Two types of enzymes have been isolated from various bacteria — pyrocatechases which catalyze catechol cleavage and protocatechuate 3,4-dioxygenases which cleave 3,4-dihydroxybenzoate (protocatechuate). The pyrocatechases have molecular weights in the 60.000-90.000 dalton range9-11) the enzyme from Pseudomonas arvilla (MW 63.000) has two subunits with the molecular form a0Fe9), while the enzyme from Acinetobacter calcoaceticus (MW 85.000) is a dimer of the form (aFe)210). 

Phenanthrene is more readily degraded than anthracene, and two different pathways are followed after cleavage of the peripheral ring in one, the naphthalene pathway via salicylate is used (Evans et al. 1965), whereas in the other o-phthalate and 3,4-dihydroxybenzoate are involved (Kiyohara et al. 1976 Kiyohara and Nagao 1978 Barnsley 1983) (Figure 6.38). The enzymes involved, l-hydroxy-2-naphthoate dioxygenase (Iwabuchi and Harayama... 

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... 

Similar reactions were reported for the broad-substrate-specific benzoate dioxygenase of Rhodococcus sp. strain 19070[2G. Recombinant E. coli containing this enzyme transform benzoate and anthranilate to catechol and 2-hydro-l,2-dihydroxybenzoate, respectively. 

---