Evidence of cytochrome P450-catalyzed cleavage of the ether bond of phenoxybutyrate herbicides in Rhodococcus erythropolis K2-3.
Bacterial strain Rhodococcus erythropolis K2-3 can cleave the ether bond of the phenoxybutyrate herbicides, i.e., 4-(2,4-dichlorophenoxy)butyrate (2,4-DB) and 4-(4-chloro-2-methylphenoxy)butyrate (MCPB), by an enzyme system that is constitutively expressed. The enzyme(s) involved were investigated in this study. The rate of disappearance of 2,4-DB determined in a whole cell assay amounted to 0.6 mmol/h x g(dry mass). Carbon monoxide difference spectra of dithionite-reduced whole cells and crude cell extracts suggested that strain K2-3 contains a soluble cytochrome P450 (P450), named P450(PB-1). The addition of various phenoxybutyrate substrates to crude cell extracts resulted in typical difference spectra following the type I pattern of substrate binding with P450. The rate of 2,4-DB cleavage was reduced by inhibitors of P450: 5 mM metyrapone and carbon monoxide at a CO/O2 ratio of 10 reduced the activity by about 20%, and 70%, respectively. The ether cleaving activity completely disappeared after disruption of the cells and could not be detected in crude extracts. To elucidate the enzymatic basis of this reaction, P450 was partially purified. With the resulting enzyme preparation, 2,4-DB cleavage activity was re-established, becoming measurable after the addition of either phenazine methosulfate or ferredoxin and ferredoxin/NADP oxidoreductase from spinach. We detected no activities attributable to alpha-ketoglutarate-dependent dioxygenase or NAD(P)H-dependent monooxygenase. These results collectively indicate that cleavage of the ether bond of phenoxybutyrate herbicides is catalyzed by P450-mediated activity in this strain. One of the products derived from this reaction is dichlorophenol, and comparative chromatographic analyses suggest that the other product is a C4-carbonic acid, most likely succinic semialdehyde/succinate.
Sträuber
Heike
H
UFZ Centre for Environmental Research, Department of Environmental Microbiology, Permoserstr. 15, D-04318 Leipzig, Germany.
Müller
Roland H
RH
Babel
Wolfgang
W
D015084:2,4-Dichlorophenoxyacetic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D008456:2-Methyl-4-chlorophenoxyacetic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D001673:Biodegradation, Environmental; D002087:Butyrates / Q000378:metabolism*; D002384:Catalysis; D002733:Chlorophenols; D002995:Clofibric Acid; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification / Q000378:metabolism*; D004986:Ether; D058607:Fibric Acids; D006540:Herbicides / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D012240:Rhodococcus / Q000201:enzymology*; D013057:Spectrum Analysis; D019802:Succinic Acid
D002087:Butyrates; D002733:Chlorophenols; D058607:Fibric Acids; D006540:Herbicides; D004986:Ether; D015084:2,4-Dichlorophenoxyacetic Acid; D002995:Clofibric Acid; C010285:fibric acid; D003577:Cytochrome P-450 Enzyme System; D019802:Succinic Acid; D008456:2-Methyl-4-chlorophenoxyacetic Acid; C116190:3,5-dichlorophenol; C008418:2-methyl-4-chlorophenoxy gamma-butyric acid; C004764:4-(2,4-dichlorophenoxy)butyric acid