BIPHENYL-ASSOCIATED META-CLEAVAGE DIOXYGENASES FROM COMAMONAS-TESTOSTERONI B-356

In addition to 2,3-dihydroxybiphenyl 1,2-dioxygenase (B1,2O), biphenyl -grown cells of Comamonas testosteroni B-356 were shown to produce a c atechol 2,3-dioxygenase (C2,3O). B1,2O showed strong sequence homology with B1,2Os found in other biphenyl catabolic pathways, while partial sequence analysis of the C2,3O of B-356 suggested a relationship with xylEII-encoded C2,3O. The coexistence of two meta-cleavage dioxygenas es in this strain prompted a comparison between the catalytic properti es of the two enzymes. C2,3O has a much broader substrate specificity than native or His-tagged B1,2O: both enzymes were inhibited by chloro catechols, but B1,2O was more sensitive than C2,3O. The results are di scussed in terms of the physiological implications of interaction betw een metabolites from the lower biphenyl-chlorobiphenyl pathway and enz ymes of the upper pathway.