Benzyl Sulfide Pathway Map

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This pathway was contributed by Nagaraja Tejoprakash, Thapar Institute of Engineering & Technology, India, and Tony Dodge, University of Minnesota, and completed by Cheng-Min Tann, Lynda Ellis and Dave Roe, University of Minnesota.

Benzyl sulfide contains a thioether bond of the type found in bis(2-chloroethyl) sulfide. Bis(2-chloroethyl) sulfide, also known as Yperite or mustard gas, is the most produced and stored chemical weapon. It is highly cytotoxic and is a carcinogenic and mutagenic alkylating agent; benzyl sulfide has been used as a non-toxic model for its metabolism.

The microbial degradation of benzyl sulfide can be carried out by white-rot (Coriolous versicolor) and brown-rot (Tyromyces palustris) fungi (Itoh et al., 1997). The initial step may be the oxidative cleavage of the C-S bond to yield benzaldehyde and benzyl mercaptan. Benzaldyde can be reduced to benzyl alcohol or oxidized to benzoate. Benzyl mercaptan can be converted to benzyl disulfide in the presense or absence of fungi. Degradation of the disulfide to the mercaptan was observed in the presence of fungi. Benzaldehyde, benzyl alcohol, and benzoate follow the toluene pathway and are finally mineralized to CO₂ and H₂O. These and several other fungi can also oxide benzyl sulfide to the sulfoxide and the sulfone (Van Hamme et al., 2003), and this may be the primary aerobic route. The first oxidation step is catalyzed by extracellular enzymes such as laccase, but the second step is cytochrome P450 (unspecific monooxygenase) mediated. Rhodococcus sp. strain IGTS8 can perform these same two oxidations using a single sulfide/sulfoxide monooxygenase (Lei and Tu, 1996).

The following is a text-format benzyl sulfide pathway map. Organisms which can initiate the pathway are given, but the 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 (8k) format.

               Benzyl sulfide                    Benzyl sulfide
            Coriolus versicolor                  Trametes trogii
            Tyromyces palustris                Tyromyces palustris
                                              Rhodococcus sp. IGTS8
                     |                             and others
                     |                                 |
                     | A                               | laccase or
                     |                                 | sulfide-sulfoxide 
                     |                                 | monooxygenase                         
                     v                                 v
     Benzaldehyde    +    Benzyl mercaptan      Benzyl sulfoxide
          |                     | ^                    |
          |                     | |                    | unspecific monooxygenase or
          |                   B | | C                  | sulfide-sulfoxide
          |                     | |                    | monooxygenase             
          |                     | |                    |        
          v                     v |                    v
        to the            Benzyl disulfide       Benzyl sulfone
   Toluene pathway

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Page Author(s): Cheng-Min Tann, Lynda Ellis and Dave Roe

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