Transformations of Dimethylsulfide - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 280

2 Enzymology of Dimethylsulfide Transformations
As outlined above, DMS is a compound that forms naturally during the enzymatic
breakdown of the algal osmolyte DMSP or the reduction of DMSO (Figure 1 ),
which is a also a major industrially used chemical and is present in the environment
as a result of natural degradation processes as well as waste disposal or pollution.
The DMS-consuming or -producing enzyme systems that will be discussed in
detail below are the DMSO reductases [EC 1.8.5.3], DMS dehydrogenases
[EC 1.8.2.4], and DMS monooxygenases [EC 1.14.13.131] (Figure 2 ). The first two
of these enzymes belong to the mononuclear molybdenum enzymes, while the third is
a FMN-dependent protein that also requires iron and magnesium as cofactors.
The reactions of DMSO reductase and DMS dehydrogenase are both reversible,
and in combination allow a continuous cycle of DMS consumption and production
(Figure 2 ).
Figure 2 Enzymatic conversion of dimethylsulfide.
DMSP lyases which also produce DMS are a very diverse group of enzymes,
where at least six different types of genes ( dddY , dddD , dddP , dddQ , dddL , dddW )
encoding proteins with different properties have been identified so far. These
enzymes have been the subject of an excellent recent review [ 14 ] and will therefore
not be covered here in detail. It should be noted, however, that the crystal structure
of the DddQ DMSP lyase including details of the enzyme's mechanism has just
been published [ 69 ].
A few other enzymes have been identified in the literature that might give rise to
DMS as part of methylation reactions. These include the trimethylsulfonium-
tetrahydrofolate N-methyltransferase [EC 2.1.1.19] that was enriched from a
bacterium referred to as an 'unusual' species of Pseudomonas capable of using
trimethylsulfonium as a source of cell carbon [ 70 ] and thioether
S-methyltransferases [EC 2.1.1.96] that are involved in the metabolism of selenium
and sulfur compounds in higher organisms [ 71 , 72 ]. However, as these enzymes do
not appear to play major roles in DMS turnover and details of their structure and
function are mostly unknown they will not be covered in detail here.