Rhodanese


Rhodanese[] is a mitochondrial enzyme that detoxifies cyanide by converting it to thiocyanate. In enzymatology, the common name is listed as thiosulfate sulfurtransferase. The diagram on the right shows the crystallographically-determined structure of rhodanese.
It catalyzes the following reaction:

Structure and mechanism

This reaction takes place in two steps. In the first step, thiosulfate is reduced by the thiol group on cysteine-247 1, to form a persulfide and a sulfite 2. In the second step, the persulfide reacts with cyanide to produce thiocyanate, re-generating the cysteine thiol 1.
Rhodanese shares evolutionary relationship with a large family of proteins, including:
  • Cdc25 phosphatase catalytic domain
  • non-catalytic domains of eukaryotic dual-specificity MAPK-phosphatases
  • non-catalytic domains of yeast PTP-type MAPK-phosphatases
  • non-catalytic domains of yeast Ubp4, Ubp5, Ubp7
  • non-catalytic domains of mammalian Ubp-Y
  • Drosophila heat shock protein HSP-67BB
  • several bacterial cold-shock and phage shock proteins
  • plant senescence associated proteins
  • catalytic and non-catalytic domains of rhodanese
Rhodanese has an internal duplication. This domain is found as a single copy in other proteins, including phosphatases and ubiquitin C-terminal hydrolases.

Clinical relevance

This reaction is important for the treatment of exposure to cyanide, since the thiocyanate formed is around 1 / 200 as toxic.:p. 15938 The use of thiosulfate solution as an antidote for cyanide poisoning is based on the activation of this enzymatic cycle.

Human proteins

The human mitochondrial rhodanese gene is TST.
The following other human genes match the "Rhodanese-like" domain on InterPro, but are not the rodanase with its catalytic activity :
Although the standard nomenclature rules for enzymes indicate that their names are to end with the letters "-ase", rhodanese was first described in 1933, prior to the 1955 establishment of the Enzyme Commission; as such, the older name had already attained widespread usage.
The systematic name of this enzyme class is "thiosulfate:cyanide sulfurtransferase". Other names in common use include "thiosulfate cyanide transsulfurase", "thiosulfate thiotransferase", "rhodanese", and "rhodanase".
Probably from ῥόδον, meaning rose, in reference to rhodanic acid which has a red colour with ferric salts.