Metamitron, a herbicide first described in 1975, has the tradenames Herbak and Glotix. Metamitron is the main residual in-crop herbicide used for the farming of sugar beets. It has a low soil retention rate and is commonly found in run off. Photo-decomposition occurs naturally in water and soil to deaminometamitron, which persists in the environment. Metamitron has a predicted half-life of 4 to 8 days depending on temperature and soil moisture.
The first published biodegradation pathway for metamitron is carried out by the Chloridazon-degradating bacteria, Rhodococcus sp. 0246b, and involves degradation of the phenyl ring. After dioxygenation, the catechol ring is cleaved via an extradiol mechanism and subsequent hydrolysis is suggested for the occurance of 2-hydroxymuconate (Blecher, et al. (1978) J Plant Disease and Plant Protection (86):93-102) (Parekh et al., 1994). Arthrobacter sp. DSM 20389 degrades metamitron via several hydrolysis steps to produce benzoylformate (Engelhardt, et al. (1982) J Agri Food Chem (30):278-282).
The following is a text-format metamitron pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic format.
Graphical Map (8K) Graphical Map (6K) Metamitron Metamitron Rhodococcus sp. 0246b Arthrobacter sp. DSM 20389 | | | | metamitron | | metamitron 2,3-dioxygenase | v amidohydrolase | | | | v v 2,3-Dihydro-2,3-dihydroxy- 2-(Acetylhydrazinylidene)- metamitron 2-phenylacetate | | | | 2,3-dihydro-2,3-dihydroxy- | | benzoylformate metamitron dehydrogenase | | deaminohydrolase | | | | v v 2,3-Dihydroxy- Benzoylformate metamitron | | | | | 2,3-dihydroxymetamitron | v 1,2-dioxygenase | to the | Mandelate | Pathway v 3-Methyl-4-amino- 6-(2-hydroxymuconate)- 1,2,4-triazin-5(4H)one | 3-Methyl-4-amino- | 6-(2-hydroxymuconate)- | 1,2,4-triazin-5(4H)one | hydrolase | | v 3-Methyl-4-amino- + 2-Hydroxymuconate 1,2,4-triazin-5(4H)one | | | v Intermediary Metabolism (KEGG)
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