TST transfers sulfur from S2O3(2-) to HCN to form HSCN

Stable Identifier
Reaction [transition]
Homo sapiens
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Cyanide is a potent metabolic poison, a major component of which is binding to and inhibition of cytochrome c oxidase (cytochrome a3), resulting in the rapid inhibition of oxidative phosphorylation (Hall & Rumack 1986). As a result, cells can't utilise oxygen, giving rise to central nervous system, cardiovascular and respiratory dysfunction that can result in permanent neurological defects and, in severe cases, death. At body's pH, cyanide exists mainly in the undissociated form hydrogen cyanide (HCN) which can cross cellular and subcellular membranes such as the blood brain barrier and mitochondrial membranes. Cyanide intoxication can occur after smoke inhalation, industrial exposure, ingestion of cyanogenic substances and cyanogenic food sources such as cassava. Antidotes for HCN poisoning cases include HCN binders, sulfur donors that convert HCN to the less toxic thiosulfate and competitors for HCN enzymatic binding sites such as NO (Petrikovics et al. 2015).

Two pathways in mammals are able to detoxify cyanide as thiocyanate via transfer of a sulfur atom: thiosulfate sulfurtransferase (TST aka rhodanese) in mitochondria and 3-mercaptopyruvate sulfurtransferase (MPST aka 3MST) in cytosol and mitochondria. TST can act to detoxify HCN by transsulfuration, that is mediating the transfer of a sulfur atom from thiosulfate (S2O3(2-)) to HCN to form the less toxic thiocyanic acid (HSCN) (Himwich & Saunders 1948, Aita et al. 1997, Zottola 2009). HSCN can be excreted in urine via the kidneys (Hamel 2011).

Literature References
PubMed ID Title Journal Year
19625201 A partial exploration of the potential energy surfaces of SCN and HSCN: implications for the enzyme-mediated detoxification of cyanide

Zottola, MA

J. Mol. Graph. Model. 2009
18872649 Enzymatic conversion of cyanide to thiocyanate


Am. J. Physiol. 1948
9070219 Cloning and expression of human liver rhodanese cDNA

Aita, N, Tanabe, S, Akamatsu, Y, Ogasawara, Y, Ishii, K

Biochem. Biophys. Res. Commun. 1997
Catalyst Activity

thiosulfate sulfurtransferase activity of TST [mitochondrial matrix]

Orthologous Events
Cross References
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