Mercaptopyruvate, from cysteine

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... 

Later studies showed that thiosulphate is derived enzymically from mercaptopyruvate (3-mercaptopyruvate cyanide sulphurtransferase E.C.2.8.I.2.), the same enzyme also catalysing the formation of thiocyanate directly from cyanide 2md mercaptopyruvate [42]. Mercaptopyruvate is produced by the deamination of cysteine (Figure 1.1). 

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