Cysteic acid decarboxylase

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.

The enzyme responsible for this action was discovered by Blaschko (18) in the liver of dogs and rats. This enzyme, cysteic acid decarboxylase, is specific for 1-cysteic acid. It is inhibited by prolonged dialysis and partially inhibited by dl-homocysteic acid on which it has no action (19). 

Medes and Floyd (87) studied the action of different tissue slices in the presence of air and ascertained the presence of cysteic acid decarboxylase in spleen, but, in contrast to Blaschko s findings, did not find it in the liver, heart, or muscles. The decarboxylating and deaminating activities of the intestinal mucosa appear at the same time the nature of the resulting product is not known to date. On the other hand, comparison of the action of slices of spleen with ground spleen, under aerobic as well as anaerobic conditions, shows that slices of spleen under both conditions, and ground spleen under anaerobic conditions, convert cysteic acid into... 

Oxidation to cysteic acid, followed by decarboxylation to taurine. Cysteic acid and cysteine sulfinic acid decarboxylase activities occur in constant ratio in various tissues, and it is likely that both substrates are decarboxy-lated by the same enzyme. In general, cysteine sulfinic acid is the preferred substrate, and there is little formation of taurine by way of cysteic acid. 

The aerobic metabolism of cystine-3 5S by chicken embryo, investigated166 both in vivo and in vitro, resulted in the formation of cystinedisulphoxide-35S (in vitro only), [35S] cystinesulphinic acid, [35S] cysteic acid, [35S]taurine and sulphate-35S. Hypotaurine has been detected neither in vivo nor in vitro. This indicates that, contrary to what had been observed in mammalian liver, hypotaurine is not the precursor of taurine in chicken embryo (equation 86). The enzyme decarboxylase, which effectively decarboxylates [35S]cysteic acid, does not act on cysteinesulphinic acid. Sulphate-35S may be produced also by the desulphination of cysteinesulphinic acid (equation 87) or from some other... 

Wu J.-Y. (1982) Purification and characterization of cysteic/cysteine sulfinic acids decarboxylase and L-glutamate decarboxylase in bovine brain Proc Natl Acad. Sci. USA 79, 4270-4274... 

Pharmacological evidence was obtained several years ago that indicated that tryptophan is decarboxylated to tryptamine by both animal and bacterial enzymes. More recent studies have failed to detect this reaction, but instead have shown decarboxylation to occur only after oxidation of the indole nucleus to yield 5-hydroxytryptophan. Decarboxylation of 5-hydroxytryptophan produces 5-hydroxytryptamine, serotonin, which has important, though incompletely defined functions in animal physiology. In some animal livers there is an enzyme that decarboxylates cysteic acid to taurine. Glutamic decarboxylase has been found in animal brain, where it is responsible for the formation of 7-aminobutyric acid. This product has been implicated in nervous function as an inhibitor of synaptic transmission. ... 

Cysteinesulfinic Acid. Cysteine is oxidized by enzyme systems present in bacteria and in liver to the corresponding sulfinic acid. It has been suggested that the unstable sulfenic acid is an intermediate in this oxidation. The nature of the reaction that produces cysteinesulfinic acid is not known. The subsequent metabolism of the sulfinic acid may proceed by any of three pathways. One involves further oxidation to cysteine-sulfonic acid, cysteic acid. The enzyme responsible has not been separated from the system responsible for the formation of cysteinesulfinic acid. Cysteinesulfonic acid is decarboxylated to taurine (I) by the decarboxylase mentioned previously (p. 284). 

Hope, D.B., 1955, Pyridoxal phosphate as the coenzyme of the mammalian decarboxylase for L-cysteine sulphinic and L-cysteic acids, Biochem. J., 59 497-500. 

The problem of regulation is complicated by the metabolic complexity of sulfur amino acids, and the wide variation in organ taurine concentrations between species. The major putative metabolic routes to taurine from cysteine are three These involve the intermediacy respectively of cysteine sulfinic acid, cysteic acid, and cysteamine. The first two utilize the enzyme cysteine sulfinic acid decarboxylase (CSAD), and the latter the enzyme cysteamine dioxygenase (CD). The distribution of these enzymes differ both quantitatively and qualitatively in corresponding organs of various species. Other pathways of taurine biosynthesis have also been proposed. For... 

The latter is decarboxylated by the action of cysteic decarboxylase and the oxidized sulfur is excreted in the form of taurine. At that time it is of interest to compare the action of desulfinicase with the action of decarboxylase. There seems to exist a certain analogy between these enzymes, just as there is an analogy between the sulfinic and carboxyl groups on which they act. But the experiments carried out to date do not show whether the desulfinicase acts by splitting off sulfur dioxide from cysteine sulfinic acid according to the equation ... 

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