Influence of chlorine substituents on rates of oxidation of chlorinated biphenyls by the biphenyl dioxygenase of Burkholderia sp strain LB400

Biphenyl dioxygenase from Burkholderia (Pseudomonas) sp. strain LB400 catal yzes the first reaction of a pathway for the degradation of biphenyl and a broad range of chlorinated biphenyls (CBs). The effect of chlorine substitu ents on catalysis was determined by measuring the specific activity of the enzyme with biphenyl and 18 congeners. The catalytic oxygenase component wa s purified and incubated with individual CBs in the presence of electron tr ansport proteins and cofactors that were required for enzyme activity. The rate of depletion of biphenyl from the assay mixture and the rate of format ion of cis-biphenyl 2,3-dihydrodiol, the oxidation product, were almost equ al, indicating that the assay accurately measured enzyme-specific activity. Four classes of CBs were defined based on their oxidation rates. Class I c ontained 3-CB and 2,5-CB, which gave rates that were approximately twice th at of biphenyl. Class II contained 2,5,3',4'-CB, 2,3,2',5'-CB, 2,3,4,5-CB, 2,3,2',3'-CB, 2, 1,5,2',5'-CB, 2,5,3'-CB, 2,5,4'-CB, 2-CB, and 3,4,5-CB, wh ich gave rates that ranged from 97 to 35% of the biphenyl rate. Class III c ontained only 2,3,4,2',5'-CB, which gave a rate that was 4% of the biphenyl rate. Class IV contained 2,4,4'-CB, 2,4,2',4'-CB, 3,4,5,2'-CB, 3,4,5,3'-CB , 3,5,3',5'-CB, and 3,4,5,2',5'-CB, which showed no detectable depletion. R ates were not significantly correlated with the aqueous solubilities of the CBs or the number of chlorine substituents on the rings. Oxidation product s were detected for all class I, II, and III congeners and were identified as chlorinated cis-dihydrodiols for classes I and II. The specificity of bi phenyl dioxygenase for the CBs examined in this study was determined by the relative positions of the chlorine substituents on the aromatic rings rath er than the number of chlorine substituents on the rings.