Transformations of Dimethylsulfide - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 281

2.1 Dimethylsulfoxide Reductases

2.1.1 Basic Properties of Dimethylsulfoxide Reductases and Their
Encoding Operons

The production of DMS from DMSO is catalyzed by a particular class of
metalloenzymes, the DMSO reductases [EC 1.8.5.3]. These enzymes are found in
a variety of bacterial phyla and especially in members of the Proteobacteria where
they are generally involved in mediating anaerobic respiration. The best-studied
DMSO reductases are the enzymes from the γ -Proteobacterium Escherichia coli

and the -Proteobacteria Rhodobacter capsulatus and Rhodobacter sphaeroides

[ 73 - 83 ] . DMSO reductases are mononuclear molybdenum enzymes, which means
that the active site contains a single Mo metal center (Figure 3 ), and within that
group of enzymes they belong to the DMSO reductase enzyme family.

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Figure 3 Schematic representation of the bis-MGD cofactor present in enzymes of the DMSO
reductase enzyme family. Only the cofactors, the central molybdenum atom, and direct ligands to
the molybdenum are shown, X ¼ amino acid ligand to the Mo center.

The DMSO reductase enzyme family is very diverse and over 25 types of
enzymes have been classified as belonging to this enzyme family [ 84 - 86 ] including
several dehydrogenases such as formate dehydrogenase, ethylbenzene dehydroge-
nase, and DMS dehydrogenase.
As a result of this diversity of enzymes that make up this enzyme family other
names have been suggested such as Complex Iron-Sulfur Molybdoenzyme family
(CISM) and Mo/W Bis-PGD enzyme family [ 73 , 84 ]. As a new name has not been
settled on at this stage, we will use the older but widely adopted designation, DMSO
reductase enzyme family.
The overall architecture of the catalytic subunits of DMSO reductase family
enzymes is similar with four (and in some cases five) clearly identifiable domains as
shown by available crystal structures [ 81 , 82 , 87 - 91 ]. However, there is great
diversity of the general architecture of the enzymes which ranges from single
subunit enzymes to membrane-bound multisubunit protein complexes with mostly