hydraulic and heat transfer fluids, plasticizers, and intermediates for chemical syntheses. Because of their toxicity, bioconcentration, and persistence, the ubiquitous distribution of halogenated compounds in the biosphere has caused public concern over the possible effects on the quality of life. Concerning toxicity, an important problem is the diversity of toxic compounds and by-products in many formulations of industrial products. This problem applies to mixtures of polychlorinated biphenyls (PCBs) or chlorinated terpenes, poly-641
Previously we purified an enzyme from Phenylobacterium immobilis DSM 1986, which cleaves the catechol derivative of the herbicide Chloridazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone] in the meta position. The enzyme, which could be crystallized, proved in Ouchterlony double-diffusion tests to consist of a single protein species. No cross-reaction was observed with other meta-cleaving enzymes. Its light absorption spectrum showed a maximum at 279 nm ( E = 310 mM-' cm-'), shoulders at 289 nm and 275 nm and a very weak band at around 430 nm ( E = 1.14 mM-' cm-'). The amino acid analysis showed a slight excess of acidic amino acids, in agreement with the PI of 4.5.Surprisingly the enzyme per se is completely inactive, although it contains one non-dialysable iron atom per subunit. It has to be activated by preincubation with ferrous ions or ascorbate. The enzyme activated this way is autoxidizable and returns to its non-activated state in the presence of oxygen. During the reaction with the substrate, this inactivation seems to be enhanced about 100 times. Since this kind of activation and inactivation is not observed in other meta-cleaving enzymes, this enzyme seems to represent a new type of a non-heme iron dioxygenase. We tentatively propose the name Chloridazon-catechol dioxygenase for this enzyme. -Amino-4-chloro-2(2',3'-dihydroxyphenyl)-3(2H)-pyri-dazinone (Chloridazon catechol) was found to be an intermediate in the degradation of the herbicide Chloridazon [5-amino-4-chloro-2-phenyl-3 (2H)-pyridazinone] by Phenylobacterium immobilis [l].We have previously purified an enzyme which cleaves the aromatic ring of this compound between the C atom bearing the heterocycle and the adjacent C atom bearing an hydroxy group, forming an unstable product which decomposes spontaneously as described earlier [2] (Fig.
Metabolism of chloridazon, the active ingredient of the herbicide Pyramin, was studied in cell suspension cultures of Beta vulgaris (sugar beet), Papaver bracteatum (poppy), Phaseolus aureus (mung bean), Glycine max (soya bean), Nicotiana tabacum (tobacco), and Petroselinum hortense (parsley). Metabolism of the analgetical and antipyretical drug antipyrin (phenazon) was also investigated. In Beta vulgaris and in Papaver bracteatum small amounts of both compounds are hydroxylated, the main quantity remaining unmetabolized. In Beta vulgaris chloridazon is converted to p-hydroxy- chloridazon, whereas antipyrin yields three different compounds, namely p-hydroxyantipyrin, hydroxymethylantipyrin and a further hydroxyantipyrin, which was identified as o- or m-hydroxy- antipyrin. Cell suspension cultures of Papaver bracteatum hydroxylate chloridazon to p- and m- hydroxychloridazon, respectively, and antipyrin to p-hydroxyantipyrin and hydroxymethylantipyrin respectively. The metabolites, with exception of o- or m-hydroxyantipyrin, were identified by spectroscopic methods. The structure of the latter metabolite was established by comparing Upvalues of the metabolite and the compound synthetically available. Metabolism in sugar beet and poppy cultures is similar to metabolism in mammals rather than in bacteria. Cell suspensions of chloridazon-insensitive sugar beet and of chloridazon-sensitive poppy are severely inhibited in growth by chloridazon, whereas antipyrin, even when applied in high concentrations, does not induce growth inhibition. In soya bean, mung bean, tobacco, and parsley neither chloridazon nor antipyrin were found to be metabolized.
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