The two-subunit meta-cleavage enzyme, 2′-aminobiphenyl-2,3-diol 1,2-dioxygenase (CarBaBb), from the carbazole degrader Pseudomonas resinovorans strain CA10 was purified to homogeneity from an Escherichia coli strain carrying the expression vector pUCA503, in which two copies of the carBaBb genes are tandemly linked. SDS-PAGE and gel filtration showed that CarB was a α2β2-heterotetrameric enzyme with subunit molecular masses of approximately 10,000 for CarBa and 29,000 for CarBb. The optimum pH for activity was 8.5 and that of temperature was 35°C. The CarB enzyme had a Kmof 14 μMand a kcat/Kmof 0.25 μM−1s−1for 2′-aminobiphenyl-2,3-diol, and the catalytic activities for biphenyl-type catecholic substrates were higher than those for monoaromatic catechol derivatives. The enzyme was originally isolated as a meta-cleavage enzyme for 2′-aminobiphenyl-2,3-diol involved in carbazole degradation, but the enzyme was highly specific for 2,3-dihydroxybiphenyl.
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