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

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).<br><br>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).

氰化物是一种强效的代谢性毒物，其主要成分通过与细胞色素c氧化酶（细胞色素a3）结合并抑制其活性，导致氧化磷酸化（Hall & Rumack 1986）的迅速抑制。因此，细胞无法利用氧气，进而引发中枢神经系统、心血管和呼吸系统的功能障碍，可能造成永久性神经缺陷，在严重病例中甚至导致死亡。在人体pH值下，氰化物主要以未解离形式氢氰酸（HCN）存在，能够穿越细胞和亚细胞膜，如血脑屏障和线粒体膜。吸入烟雾、工业暴露、摄入含氰化合物和含氰食物来源（如木薯）后都可能发生氰化物中毒。针对氢氰酸中毒的抗毒剂包括氢氰酸结合剂、硫供体（将HCN转化为毒性较低的硫代硫酸盐）以及竞争性抑制剂，如一氧化氮（NO，Petrikovics et al. 2015）。哺乳动物中存在两种途径能够通过转移硫原子将氰化物转化为硫氰酸盐进行解毒：线粒体内的硫代硫酸盐硫转移酶（TST，亦称硫氰酸酶）和细胞质及线粒体内的3-巯基丙酮酸硫转移酶（MPST，亦称3MST）。TST能够通过转硫作用解毒HCN，即通过介导硫原子从硫代硫酸盐（S2O32-）转移到HCN，形成毒性较低的硫氰酸（HSCN）（Himwich & Saunders 1948，Aita et al. 1997，Zottola 2009）。HSCN可以通过肾脏随尿液排出（Hamel 2011）。