Thiosulfate, from cysteine

Figure 5.3. Growth of vitamin Bn-depleted and vitamin Bn-deficient cells ofP. shermanii in different redox environments. A wild-type cells deprived of cobalt (residual vitamin B about 10 pg/g) were grown in the absence of cobalt (1), under argon gas (2) or in the presence of C0CI2 6H2O at 3 mg/1 (3). In 3, the fmal level of vitamin B12 was 1500 pg/g. B vitamin Bi2-deficient mutant cells were grown in the absence of cobalt (1), but in the presence of 0.03% each of the following reduced glutathione (2), sodium thiosulfate (3), cysteine (4), methionine (5) or tryptone (6). From Iordan et al. (1984).

HCN is detoxified to thiocyanate (SCN ) by the mitochondrial enzyme rhodanese rhodanese catalyzes the transfer of sulfur from thiosulfate to cyanide to yield thiocyanate, which is relatively nontoxic (Smith 1996). The rate of detoxification of HCN in humans is about 1 pg/kg/min (Schulz 1984) or 4.2 mg/h, which, the author states, is considerably slower than in small rodents. This information resulted from reports of the therapeutic use of sodium nitroprusside to control hypertension. Rhodanese is present in the liver and skeletal muscle of mammalian species as well as in the nasal epithelium. The mitochondria of the nasal and olfactory mucosa of the rat contain nearly seven times as much rhodanese as the liver (Dahl 1989). The enzyme rhodanese is present to a large excess in the human body relative to its substrates (Schulz 1984). This enzyme demonstrates zero-order kinetics, and the limiting factor in the detoxification of HCN is thiosulphate. However, other sulfur-containing substrates, such as cystine and cysteine, can also serve as sulfur donors. Other enzymes, such as 3-mercapto-pyruvate sulfur transferase, can convert... 

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... 

We may divide the sulfur compounds into primary and conjugated, the primary compounds forming a part of more complex chemical structures in the latter. The major primary sulfur compounds that have an established role in the normal biochemical processes of the vertebrate range in variety from the simple inorganic compounds, sulfate, thiosulfate, and thiocyanate, to the amino acids, cysteine, cystine, methionine,... 

In contrast to the fact that Z-cysteine alone can be utilized for growth, oxidation in the living animal of the sulfur from d- or Z-cysteine seems to proceed equally well. Among the products resulting from this oxidation cystine, sulfate, thiosulfate, and taurine have been identified. 

---