Sulfurtransferase

Sulfurtransferasen are enzymes that transfer sulfur-containing groups of a sulfur donor to a nucleophilic sulfur acceptor. They form a common class of enzymes because of their catalytic reaction. Sulfurtransferasen are widespread in archaea, eubacteria and eukaryotes. In plants, they occur in different compartments of the cell, in the cytoplasm, in mitochondria, in the plastids, and possibly in the peroxisomes.

Construction

Sulfurtransferasen encoded in most organisms by the same gene family. Distinguishing feature is the Rhodanasedomäne, consisting of a tandem repeat. The C-terminal domain contains the L- cysteine ​​of the active site. There are Sulfurtransferasen with one and those with two Rhodanasedomänen and Sulfurtransferasen with inactive Rhodanasedomäne. Two domain Sulfurtransferasen consist of two globular domains linked by a short amino acid chain ( linker).

Reaction

The best characterized is the Rinderrhodanase from the liver. The substrates of the Rinderrhodanase are thiosulfate and cyanide. The products are thiocyanate and sulfite. The sulfur is transferred in vitro from thiosulfate to cyanide. Cyanide is oxidized to thiocyanate and thiosulfate to sulfite.

The reaction proceeds in two steps. In the first step is caused by a persulfide transfer of the sulfur atom of a sulfur donor in the catalytic center of the thiosulfate Rinderrhodanese on L - cysteine ​​residue Cys -247 of the active site. The persulfide is dissolved in the second step, whereby the sulfur atom is transmitted to the cyanide.

The transfer of the sulfur atom is catalyzed by the L- cysteine ​​Cys- 243, at the substrate binding appear L-arginine -186 and L-lysine -249 to be involved.

Function

The exact function of Sulfurtransferasen is not known, but a number of possible functions will be described: the detoxification of cyanide in which the substantially non-toxic thiocyanate formed. Detoxification of free oxygen radicals by thioredoxin reductase. Other functions include participation in the assimilation of sulfate, and the provision of reduced sulfur for biosynthesis, eg for iron-sulfur cluster. An assisting in the mobilization and transport of reduced sulfur, during senescence in newly grown plant organs, is also proposed. Also play a role in pathogen defense is regarded as a potential function.

Enzyme classification

The Sulfurtransferasen (. EC 2.8.1 - ) form eight sub-groups:

• Thiosulfate sulfurtransferase ( EC 2.8.1.1 )
• 3- Mercaptopyruvat - sulfurtransferase ( EC 2.8.1.2 )
• Thiosulfate -thiol sulfurtransferase ( EC 2.8.1.3 )
• TRNA sulfurtransferase ( EC 2.8.1.4 )
• Thiosulfate -dithiol - sulfurtransferase ( EC 2.8.1.5 )
• Biotin - synthase (EC 2.8.1.6 )
• Cysteine ​​desulfurase ( EC 2.8.1.7 )
• Lipoyl synthase (EC 2.8.1.8 )