Rhodanese is a
mitochondrial enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
that detoxifies
cyanide
In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom.
Ionic cyanides contain the cyanide anion . This a ...
(CN
−) by converting it to
thiocyanate (SCN
−, also known as "rhodanate").
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:
:thiosulfate + cyanide
sulfite + thiocyanate
Structure and mechanism
This reaction takes place in two steps. In the first step,
thiosulfate
Thiosulfate ( IUPAC-recommended spelling; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula . Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, ...
is reduced by the
thiol group on
cysteine
Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...
-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.
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 (see also the list of related families in
#Structure and mechanism):
* M-phase inducer phosphatase:
CDC25A;
CDC25B;
CDC25C;
* Dual specificity protein phosphatase:
DUSP;
DUSP1;
DUSP2;
DUSP4;
DUSP5;
DUSP6;
DUSP7;
DUSP10;
DUSP16, aka MKP7;
* Thiosulfate:glutathione sulfurtransferase:
KAT, now known as "
TSTD1";
* Adenylyltransferase and sulfurtransferase:
MOCS3;
* 3-mercaptopyruvate sulfurtransferase:
MPST, also known as "TSTD2"
* Not an enzyme:
TBCK;
TSGA14;
* Ubiquitin carboxyl-terminal hydrolase:
USP8;
* Unknown activity: TSTD3
Nomenclature
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
A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature.
A semisystematic name or semitrivi ...
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 (ródon), meaning rose, in reference to
rhodanic acid which has a red colour with ferric salts.
[https://www.websters1913.com/words/Rhodanic]
References
External links
*
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EC 2.8
Protein domains