Hypotaurine from cysteine sulfinate

Fig. 24-25), another component of nervous tissue. Cysteic acid can arise in an alternative way from O-acetylserine and sulfite (reaction 1, Fig. 24-25), and taurine can also be formed by decarboxylation of cysteine sulfinic acid to hypotaurine and oxidation of the latter (reaction m). Cysteic acid can be converted to the sulfolipid of chloroplasts (p. 387 Eq. 20-12). 

Figure 14.7. Pathways for the synthesis of taurine from cysteine. Cysteine sulfinate decarboxylase, EC 4.1.1.29 cysteic acid decarboxylase, EC 4.1.1.29 (glutamate decarboxylase, EC 4.1.1.15) cysteine oxidase, EC 1.13.11.20 cysteamine oxygenase, EC 1.13.11.19 and hypotaurine oxidase, EC 1.8.1.3. Relative molecular masses (Mr) cysteine, 121.2 cysteamine, 77.2 cysteine sulfinic acid, 153.2 cysteic acid, 169.2 hypotaurine, 109.1 and taurine, 125.1.

An alternate possibility is a direct oxidation of cysteine to sulfenic and sulfinic acid (16), Eq. (3). Medes and Floyd (17) observed that a particulate preparation of liver homogenate catalyzes the production of CO from cystine and it was suggested that cystine may be oxidized to the disulfoxide which is then decarboxylated to cystamine disulfoxide Eq. (4). The latter could be converted to hypotaurine and then to taurine. The sequence of these hypothetical reactions is as follows ... 

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