Sulfane sulfur

Another enzyme, cysteine desulfurase, converts L-cysteine to L-alanine and a sulfane sulfur - a chain of divalent sulfur atoms. A protein-bound cysteine persulfide is formed on a conserved cysteine residue. Such enzymes have important roles in the biosynthesis of Fe-S clusters and sulfur-containing cofactors.9... 

The metabolism of cyanide has been studied in animals. The proposed metabolic pathways shown in Figure 2-3 are (1) the major pathway, conversion to thiocyanate by either rhodanese or 3-mercapto-pyruvate sulfur transferase (2) conversion to 2-aminothiazoline-4-carboxylic acid (Wood and Cooley 1956) (3) incorporation into a 1-carbon metabolic pool (Boxer and Richards 1952) or (4) combining with hydroxocobalamin to form cyanocobalamin (vitamin B12) (Ansell and Lewis 1970). Thiocyanate has been shown to account for 60-80% of an administered cyanide dose (Blakley and Coop 1949 Wood and Cooley 1956) while 2-aminothiazoline-4-carboxylic acid accounts for about 15% of the dose (Wood and Cooley 1956). The conversion of cyanide to thiocyanate was first demonstrated in 1894. Conversion of cyanide to thiocyanate is enhanced when cyanide poisoning is treated by intravenous administration of a sulfur donor (Smith 1996 Way 1984). The sulfur donor must have a sulfane sulfur, a sulfur bonded to another sulfur (e.g., sodium thiosulfate). During conversion by rhodanese, a sulfur atom is transferred from the donor to the enzyme, forming a persulfide intermediate. The persulfide sulfur is then transferred... 

Cyanide is metabolized in the body by two metabolic pathways that have been identified (Ansell and Lewis 1970). The first and major metabolic pathway involves the transfer of sulfane sulfurs from a donor to cyanide to yield thiocyanate (see Section 2.3). The reaction employs the enzyme rhodanese as a... 

An increase in antidotal effect was noted when rhodanese was combined with thiosulfate (Frankenberg 1980). Similarly, other sulfane sulfur donors have protective effects against cyanide toxicity. 

Although these equations held true for some strains of bacteria under some growth conditions, they did not help explain the commonly observed quantitative conversion of both sulfur atoms of thiosulfate to sulfate, rather than the liberation of the sulfane-sulfur mainly as elemental sulfur. During the 1960s, cyclic reactions of polythionates and other polysulfur compounds continued to be postulated as mechanisms for thiosulfate and polythionate metabolism (Trudinger 1967), but none of these was supported at the time by strong biochemical evidence. The time was opportune for a new approach to the problem of thiosulfate oxidation in thiobacilli. 

It now seems probable that cleavage of thiosulfate in T. thioparus (and Thiobacillus denitrificans) depends not on a reductase as originally perceived by Peck (1960) but on a sulfur transferase of the rhodanese type (Peck 1968). Rhodanese is usually detected by its ability to transfer the sulfane-sulfur of thiosulfate to the nonphysiologic acceptor cyanide, producing thiocyanate and liberating sulfite ... 

Oxidation of the Sulfane-Sulfur of Thiosulfate and the Resynthesis of the Sulfonate Group of Thiosulfate from Sulfane-Sulfur by Thiobacilli... 

The molecular structures of several polysulfane tetroxides of this type have been elucidated by X-ray diffraction on single crystals. The S-S bonds between the sulfone groups and the neighboring sulfane sulfur are weaker (210-214 pm) than ordinary S-S single bonds (205 pm). ... 

SYNS SULFAN SULFURIC ANHYDRIDE SULFURIC OXIDE SULFUR TRIOXIDE, inhibited (UN 1829) (DOT) SULFUR TRIOXIDE, uninhibited (NA 1829) (DOT)... 

Cyanide is rapidly absorbed from the skin and all mucosal surfaces it is most dangerous when inhaled because toxic amounts are absorbed with great rapidity through the bronchial mucosa and alveoli. Once absorbed, distribution of cyanide through the body is rapid. Within a few minutes, cyanide is distributed through the body and its conversion to thiocyanate starts. The majority of cyanide in the body is protein-bound (60%). In sublethal doses, cyanide reacts with sulfane sulfur to form nontoxic... 

Rhodanese is present in the mitochondria, particularly of liver and kidney cells. A double-displacement mechanism has been proposed for its biochemical action. The steps are as follows The free enzyme reacts with a sulfane sulfur-containing compound (a sulfane sulfur is one that is divalent and covalently bonded only to other sulfurs), cleaving the S-S bond of the donor substrate (e.g., SSOj ) to form the sulfur-substituted enzyme. The latter reacts with the cyanide (a thiophilic acceptor) to form thiocyanate in an essentially irreversible reaction. 

The basic reaction involves transfer of sulfane sulfur from the donor (SCN) to the enzyme, forming a persulhde intermediate. The persulfide sulfur is transferred from the enzyme to a nucleophilic receptor (CN) to yield SCN. For most species, this enzyme activity is high in liver, kidney, brain, muscle, and olfactory mucosa (Himwich and Saunders, 1948 Dahl, 1989 Aminlari et al., 1994). The nasal metabolism of CN may have relevance to the toxicity of inhaled HCN. (3-Mercaptopymvate-cyanide transulfurases are present in blood, liver, and kidney, and catalyze the reaction ... 

A third sulfurtransferase, cystathionase (cystathionine y-lyase EC 4.4.1.1), which is a cytosohc enzyme, may play a role in CN detoxification in the kidney and rhombencephalon (Wrobel et al., 2004). A product of the cystathionase reaction, bis(2-amino-2-carboxylethyl)trisulfide (thiocystine), may serve as a sulfur substrate donor for rhodanese. Another reaction product, 3-(thiosulpheno)-alanine (thiocysteine), may be an additional link between cystathionase and CN biodetoxification. In addition, cystathionase also functions as a sulfane sulfur carrier. 

Westley J (1981). Cyanide and sulfane sulfur. In Cyanide in Biology (B Vennesland, EE Conn, CJ Knowles et al., eds), pp. 61-76. London, UK Academic Press. 

Thiosulfate (S2O3 ) is composed of an inner sulfonate sulfur (-SO3) and an outer sulfane sulfur (-S), and by expectation, the sulfate produced during disproportionation (Eqn. 12) should be derived from the sulfonate sulfur, whereas sulfide should be derived from the sulfane sulfur. Isotope fractionation during thiosulfate disproportionation has been explored with pure bacterial cultures under two contrasting experimental circumstances. In one case, sulfide, a byproduct of the disproportionation process, was allowed to accumulate within the experimental system (Habicht et al. 1998) whereas in the other case sulfide was actively purged from the experimental system and never reached a concentration greater than 0.4 mM (Cypionka et al. 1999). 

The utility of thiosulfate is limited because of its short biological half-life and its small volume of distribution.23 This combination of pharmacological properties, in addition to the suggestion that the presence of cyanide increases the intracellular availability of the thiosulfate,63 indicates that this compound probably cannot be used as a prophylactic but only as an antidote. Compounds containing the more-lipophilic sulfane sulfur (R—S—S ) or compounds that can be actively transported into the cells may be more beneficial as cyanide antagonists,64 66 but none are commercially available. 

Westley J. Cyanide and sulfane sulfur. In Vennesland B, Conn EE, Knowles CJ, Westley J, Wissing F, eds. Cyanide in Biology. New York, NY Academic Press 1981 61-76. 

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 ... 

All of these biological functions of thiocystine can be attributed to the persulfide nature of the trisulfide. The term persulfide is used to describe compounds that can transfer sulfane sulfur to appropriate acceptors. On the basis of its similarity to thiosulfate in functioning as a substrate for rhodanese, other biological transfer reactions can be predicted for thiocystine. 

Abdolrasulnia and Wood ° showed that labeled thiocystine transferred only sulfane sulfur to rhodanese when the persulfide was formed. 

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