2‐Aminobenzoyl‐CoA monooxygenase/reductase, a novel type of flavoenzyme

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Abstract
The reaction catalyzed by 2-aminobenzoyl-coenzyme-A monooxygenase/reductase from a denitrifying Pseudomonas sp. has been investigated. 2-Aminobenzoyl-CoA and 2-amino[carboxy-14C]benzoyl-CoA were synthesized enzymatically using 2-aminobenzoyl-CoA synthetase form the same organism. The product was purified by chromatography and characterized by ultraviolet/visible and 1H-NMR spectroscopy. The conversion of 2-aminobenzoyl-CoA catalyzed by the monooxygense/reductase requires NADH and oxygen, and yields at least two different products depending on the relative concentration of NADH. At [NADH] < K/m (40 .mu.m), i.e. [NADH]/[2-aminobenzoyl-CoA].apprxeq. 0.02-0.5, the main product is probably a hydroxylated derivative of 2-aminobenzoyl-CoA, which is characterized by an absorbance maximum around 375 mm. When [NADH]/[2-aminobenzoyl-CoA] .apprxeq. 2-5, the predominant product is a non-aromatic coenzyme A thioester (.LAMBDA.max .apprxeq. 320 nm). The stoichemistry in this case is 2.1-2.4 mol NADH oxidized (mol oxygen consumed)-1 (mol 2-aminobenzoyl-CoA metabolized)-1. The product is extremely unstable in the acidic pH range and undergoes decarboxylation in a few minutes at pH < 5. Some degree of stabilisation is obtained upon reduction with sodium borhydride, probably resulting in a further reduced non-aromatic coenzyme-A thioester.