Halohydrins, including 1,3-dichloro-2-propanol (DCP) and 3-chloro-1,2-epoxypropane (epichlorohydrin), are suspected of being carcinogenic, mutagenic and genotoxic. Epichlorohydrin is a synthetic precursor of DCP, which is used as a general solvent, as an intermediate in organic synthesis and in paints, varnishes, lacquers, water colors, binders and photographic lacquers.
Two pathways for the degradation of DCP are found in Corynebacterium sp. strain N-1074 which are catalyzed by two groups of two isoenzymes (Nakamura et al., 1992). One group of two enzymes, originally designated Ia and IIa, catalyzes the non-stereospecific dechlorination and subsequent hydrolyzation of DCP. Both enzymes accept (R)- and (S)-enantiomers as substrates and convert them to racemic product mixtures (Nakamura et al., 1994). The second group of enzymes, designated Ib and IIb, also accept (R)- and (S)-enantiomers, but convert them to (R)-rich products (Nakamura et al., 1992). Comparisons of protein sequences and immunological properties have shown that halohydrin hydrogen-halide-lyase (HHHL) A (enzyme Ia) is similar, but not identical to HHHL B (enzyme Ib) (Nakamura et al., 1994). Epoxide hydrolase A (enzyme IIa) and epoxide hydrolase B (enzyme IIb) have also been shown to have different structural properties (Nakamura et al., 1992).
Although Arthrobacter sp. strain AD2 can dechlorinate DCP and 3-Chloro-1,2-propanediol, it does not possess epoxide hydrolase activity and so cannot use either compound as a sole carbon source. Partial sequence comparisons have shown that the HHHL of strain AD2 is very similar to the Corynebacterium HHHL A (Nagasawa et al., 1992, Appl. Microbiol. Biotechnol. 36:478-482).
Another species, Agrobacterium radiobacter strain AD1, can use DCP or epichlorohydrin as a sole carbon source. The pathway of degradation is non-enantioselective and similar to that of the Corynebacterium strain. The AD1 epoxide hydrolase has been shown to be very similar to the Corynebacterium epoxide hydrolase A. The HHHL however, is both sequentially and immunologically different from HHHL A and HHHL B (Rink et al., 1997).
The following is a text-format 1,3-dichloro-2-propanol 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 (14k) format.
1,3-Dichloro-2-propanol 1,3-Dichloro-2-propanol Arthrobacter sp. strain AD2 Corynebacterium sp. strain N-1074 Corynebacterium sp. strain N-1074 | | | | | | halohydrin hydrogen- | halohydrin hydrogen- | halide-lyase A | halide-lyase B | | v v (RS)-3-Chloro-1,2-epoxypropane (R)-3-Chloro-1,2-epoxypropane (Epichlorohydrin) | | | | | | epoxide hydrolase A | epoxide hydrolase B | | | | v v (RS)-3-Chloro-1,2-propanediol (R)-3-Chloro-1,2-propanediol | | | | | halohydrin hydrogen- | halohydrin hydrogen- | halide-lyase A | halide-lyase B | | | | v v (RS)-3-Hydroxy-1,2-epoxypropane (R)-3-Hydroxy-1,2-epoxypropane \ / \ / \ / \ / \ epoxide / epoxide \ hydrolase A / hydrolase B \ / \ / \ / \ / \ / v v Glycerol | | | | | v Intermediary Metabolism KEGG
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