Thiosulfate: cyanide sulfurtransferase

Thiosulfate cyanide sulfurtransferase symmetry in 78 TTiiouridine 234 Three-dimensional structures of aconitase 689 adenylate kinase 655 aldehyde oxido-reductase 891 D-amino acid oxidase 791 a-amylase, pancreatic 607 aspartate aminotransferase 57,135 catalytic intermediates 752 aspartate carbamyltransferase 348 aspartate chemoreceptor 562 bacteriophage P22 66 cadherin 408 calmodulin 317 carbonic acid anhydrase I 679 carboxypeptidase A 64 catalase 853 cholera toxin 333, 546 chymotrypsin 611 citrate synthase 702, 703 cutinase 134 cyclosporin 488 cytochrome c 847 cytochrome c peroxidase 849 dihydrofolate reductase 807 DNA 214, 223,228,229, 241 DNA complex... 

Examples of typical enzyme names are arginase, which acts on arginine, and urease, which acts on urea (Chap. 15). Two atypical common names are pepsin, a digestive tract proteolytic enzyme (EC number 3.4.23.1), and, more exotically, rhodanese (thiosulfate cyanide sulfurtransferase, EC 2.8.1.1), which is in mammalian liver and kidney and catalyzes the removal of cyanide and thiosulfate from the body. In the latter case, it is understandable why the old name has remained in common use. 

Rhodanese (thiosulfate cyanide sulfurtransferase EC 2.8.1.1 ) is a mitochondrial enzyme which transfer sulfane sulfur of thiosulfate by a double displacement mechanism involving a sulfur-substituted enzyme ... 

The two enzyme systems responsible for the transulfuration process are thiosulfate-cyanide sul-furtransferase — also known as rhodanese — and beta-mercaptopyruvate cyanide sulfurtransferase. 

Figure 47.4 Metabolic pathway of cyanide. The cyanide in the cells can be rapidly detoxified by cyanide sulfurtransferase (known as rhodanese). The majority of cyanide in vivo is enz5miatically converted to SCN and excreted in the urine. The remaining cyanide is metabolized mainly via two other routes (i) production of 2-amino-4-thiazolmecarboxylic add from cystine and cyanide, and (ii) synthesis of cyanocobalamin via the combination of cyanide with some other of vitamin B12 analogue, such as hydroxycobala-min or methylcobalamin (Boxer and Richards 1952). CN cyanide Na2S203 sodium thiosulfate SCN thiocyanate CN-B12 cyanocobalamin HCN hydrocyanic acid HCNO cyanic acid HCOOH formic acid.

Cyanide is readily detoxified in animals as all animal tissues contain the thiosulfate sulfurtransferase enzyme rhodanese. Rhodanese readily converts cyanide to the thiocyanate which is excreted in the urine. 

An important property of 3-mercaptopyruvate arises from electron withdrawal by the carbonyl group. This makes the SH group electrophilic and able to be transferred as SH+, S°, to a variety of nucleophiles (Eq. 24-44). Thus sulfite yields thiosulfate (S2032 + H+, Eq. 24-45, step a), cyanide yields thiocyanate (Eq. 24-45, step b), and cysteine sulfinate yields alanine thiosulfonate.448 461 The reactions are catalyzed by mercaptopyruvate sulfurtransferase, an enzyme very similar to thiosulfate sulfurtransferase. The latter is a liver enzyme often called by the traditional... 

At lease four intracellular enzymes may be involved for cyanide detoxification. The generalized reactions of rhodanese, mercaptopyruvate sulfurtransferase, thiosulfate reductase, and cystathionase are shown within the cell. 

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