Taurine cysteine conversion

Oxidation of Cystine, Cystine has been reported to initiate a series of reactions in which the S—S bond remains intact. An oxidation product is cystine disulfoxide, RSOSOR. This compound can yield both cysteine and sulfate in the intact rat, but most of it is converted to taurine. Both carboxyl groups of cystine disulfoxide are removed by a decarboxylase different from cysteic decarboxylase. Oxidation and hydrolysis of the decarboxylation product would yield two equivalents of taurine, but the individual steps of this conversion have not been isolated. 

Enzyme preparations that oxidize cysteine to cysteic acid have been obtained from liver. Conversion of cysteic acid to taurine was indicated by Virtue and Doster-Virtue, who observed an increase in the output of taurocholic acid in the bile of dogs upon administering cysteic acid along with cholic acid. 

Other pathways for the partial degradation of cysteine are its conversion to cysteamine and taurine. These processes are discussed in Chapter 16. 

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