Dihydroxylation and dechlorination of chlorinated biphenyls by purified biphenyl 2,3-dioxygenase from Pseudomonas sp. strain LB400

Abstract

Oxidation of biphenyl and nine chlorinated biphenyls (CBs) by the biphenyl 2,3-dioxygenase from Pseudomonas sp. strain LB400 was examined. The purified terminal oxygenase required the addition of partially purified electron transport components, NAD(P)H, and ferrous iron to oxidize biphenyl and CBs. cis-Biphenyl 2,3-dihydrodiol was produced with biphenyl as the substrate. Dihydrodiols were produced from all CBs, and more than one compound was produced with most substrates. Catechols were produced when the dioxygenasecatalyzed reaction occurred at the 2,3 position of a 2-chlorophenyl ring, resulting in dechlorination of the substrate. Oxidation at the 3,4 position of a 2,5-dichlorophenyl ring produced a 3,4-dihydrodiol. Compounds resulting from both types of reaction were produced during oxidation of 2,5,2-trichlorobiphenyl. The broad substrate specificity and the ability to oxidize at different ring positions suggest that the biphenyl 2,3-dioxygenase is responsible for the wide range of CBs oxidized by Pseudomonas sp. strain LB400.

Aerobic degradation of polychlorinated biphenyls by Alcaligenes sp. JB1: metabolites and enzymes

“…Thus, when 2,2',3,3',6,6'-hexachlorobiphenyl was degraded in the chemostat culture experiments it is likely that 3,4-dihydroxy 3,4-dihydro-(2,2',3',5,6,6'-hexachloro)biphenyl was the end product. Accumulation of 3,4-dihydroxy 3,4-dihydro(nchloro)biphenyls in resting-cell assays has been reported by Nadim et al (1987) and in enzyme assays by Haddock et al (1995). Alternatively, 3,4-dihydroxy (2,2',3',5,6,6'-hexachloro)biphenyl might be the endproduct of 2,2',3,3',6,6'-HCB degradation in JB 1.…”

“…It is possible that energy may have to be invested in the first steps of aerobic PCB metabolism. Indeed, Haddock et al (1995) showed that the biphenyl 2,3-dioxygenase from Pseudomonas sp. LB400 required the addition of NAD(P)H and reduced iron (Fe2+).…”

“…The relative persistence of ortho substituted congeners suggests that the biphenyl dioxygenase that attacks 2-chlorophenyl rings in JB1 differs from the enzyme present in strains LB400 and H850. The latter strains both exhibit high activity against 2,2'-DCB (Bedard et al 1986;Bedard & Haberl, 1990), presumably because they express a biphenyl 2,3-dioxygenases that can attack at the ortho chlorinated position (Bedard, 1990;Haddock et al 1995). From the enzyme assays it is clear that 3,4-dihydroxybiphenyl dioxygenase activity is not present in JB1.…”

An aryl dioxygenase shows remarkable double dioxygenation capacity for diverse bis-aryl compounds, provided they are carbocyclic

“…However, only in a few cases has direct or indirect evidence for such a reaction been obtained. Haddock et al (1995), working with BphA-LB400, reported, on the grounds of GC-MS data, the likely 3,4,3',4'-bis-DHD formation exclusively from 2,5,2',5'-tetrachlorobiphenyl among a range of chlorobiphenyls investigated. Kimura et al (1996), studying biotransformations by the mutant strain Pseudomonas sp.…”

“…As this modulation critically depends on the active site architecture, it should be enzyme-specific. With the ARHDO catalytic mechanism outlined above, observations like the preferred dioxygenations of 2,2'-dichlorobiphenyl at carbons 2 and 3 (Haddock et al 1995;Seeger et al 1995) and the double dioxygenation of 2,5,2',5'-tetrachlorobiphenyl (Haddock et al 1995) appear difficult to be interpreted alone by electronic influences on the reaction mechanism. This is underpinned by the findings that these specific dioxygenations are shown only by some ARHDOs, but not by others that accept these substrates.…”