Sulfinate and Taurine

Rhodococcus sp. Strain T09 A Rhodococcus strain T09 was isolated by enrichment on media-containing BT. The desulfurization mechanism of this organism was reported to be similar to Gordonia sp. 213E due to the observation of similar intermediates however, the substrate specificity was different. The strain T09 could use 2-methyl, 3-methyl and 5-methyl BT apart from BT as sole source of sulfur for growth, but not 7-methyl or ethyl derivatives. Additionally, it could also use methyl thiobenzothiazole, marcaptobenzothiazole, as well as benzene sulfide, benzene sulfonate, biphenyl sulfinate, dimethyl sulfate, dimethyl sulfone, dimethyl sulfide, methane sulfonic acid, thiophene, and taurine as sole sulfur sources. However, it could not grow on DBT or DBT sulfone. 

The desulfinase enzyme was reported to have narrow substrate specificity. In addition to HBPSi, only 2-phenyl benzene sulfinate was reported to serve as a substrate [164], It was found to be inactive against benzene sulfinate, cysteine sulfinate, benzene sulfonate, /7-toluene sulfonate, 1-octane sulfonate, methane sulfonate, and taurine. This enzyme was found to be inhibited by HBP beginning at 0.5 mM with complete loss of activity at 9 mM HBP, but was not affected by sulfite. 

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.

Eluted at the very front of the chromatogram (the most acidic amino acids) are phosphoethanolamine, cysteic acid, cysteine sulfinic acid, taurine (Tau), and glyceryl phosphoethanolamine These compounds are not well separated, especially with the very fast amino acid analysis systems. A system has been described using O.IM citric acid (DeMarco et al., 1965a,b), but for better separation of this area of the chromatogram, special anion-exchange chromatographic techniques may be needed Fortunately, in plasma one is likely to encounter only Tau and in most samples the accurate analysis of only Tau and phosphoethanolamine should be considered. 

Sulfinic acids, e.g., L-cysteine sulfinic acid and hypotaurine, and sulfonic acids, e.g., L-cysteic acid and taurine, are naturally occurring products of L-cysteiiie and cysteamine oxygenation. They occur in microorganisms, plants, and animals. 

L-Cysteine is transformed to L-cysteine sulfinic acid and L-cysteic acid. Cysteamine (D 11) yields hypotaurine and taurine (Fig. 189). The latter compounds may be transformed to other secondary products by deamination, thiolation, guanylation, and methylation. L-Cysteine sulfinic acid may be degraded to L-alanine and sulfurous acid, which is oxidized to sulfuric acid. 

It was also demonstrated (38) that an enz3rme system of the calf embryo converts SO (in the presence of pyruvate and glutamate) to cysteine sulfinate and hypotaurine. Taurine and cystine, products of reactions catalyzed by enzymes of rabbit liver, (31) are not formed by liver extracts of the calf embryo. 

C. Loriette, H. Pasantes-Morales, C. Portemer and F. Chatagner, Dietary Casein Levels and Taurine Supplementation Effects on Cysteine Dioxygenase and Cysteine Sulfinate Decarboxylase Activities and Taurine Concentration in Brain, Liver and Kidney of the Rat, Nutr. Metab. (in press). 

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 ... 

A quantitatively important pathway of cysteine catabolism in animals is oxidation to cysteine sulfinate (Fig. 24-25, reaction z),450 a two-step hydroxyl-ation requiring 02, NADPH or NADH, and Fe2+. Cysteine sulfinic acid can be further oxidized to cyste-ic acid (cysteine sulfonate),454 which can be decarbox-ylated to taurine. The latter is a component of bile salts (Fig. 22-16) and is one of the most abundant free amino acids in human tissues 455-457 Its concentration is high in excitable tissues, and it may be a neurotransmitter (Chapter 30). Taurine may have a special function in retinal photoreceptor cells. It is an essential dietary amino acid for cats, who may die of heart failure in its absence,458 and under some conditions for humans.459 In many marine invertebrates, teleosts, and amphibians taurine serves as a regulator of osmotic pressure, its concentration decreasing in fresh water and increasing in salt water. A similar role has been suggested for taurine in mammalian hearts. A chronically low concentration of Na+ leads to increased taurine.460 Taurine can be reduced to isethionic acid... 

Some pyridoxal phosphate-dependent enzymes are normally fuUy saturated with cofactor and show the same activity on assay in vitro whether additional pyridoxal phosphate is present in the incubation medium or not. Examples of this class of enzymes include liver cysteine sulfinate decarboxylase (which is involved in the synthesis of taurine from cysteine Section 14.5.1) and the brain and liver glutamate and aspartate aminotransferases. 

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. 

In the liver and brain, the main pathway is by way of cysteine sulfinic acid, whereas in tissues with low cysteine sulfinic acid decarboxylase activity the main precursor of taurine is cysteamine. 

It is not known to what extent taurine may be a dietary essential for human beings. There is little cysteine sulfinic acid decarboxylase activity in the human liver and, like the cat, loading doses of methionine and cysteine do not result in any significant increase in plasma taurine. This may be because cysteine sulfinic acid can also undergo transamination to /3-sulfhydryl pyruvate, which then loses sulfur dioxide nonenzymically to form pyruvate, thus regulating the amount of taurine that is formed from cysteine. There is no evidence of the development of any taurine deficiency disease under normal conditions. 

FIGURE 2.40 The major pathway for taurine biosynthesis in the liver- First, cy teine is converted to cysteine sulfinic acid in an oxygen-requiring reaction catalyzed by an iron metalloeozyme- The second step, catalyzed by a vitamin B -requiring enzyme, is a decarboxylation reaction. The final step appears to be catalyzed by a copper metaLloenzyme and to require oxygen. Apparently, about one-fourth of the cysteine in the liver eventually is converted to taurine. 

Oxidation to cysteine sulfinic acid, followed by decarboxylation to hypo-taurine and oxidation to taurine. In most tissues, it is the decarboxylation... 

Chan-Palay V, Lin CT. Palay SL, Yamamoto M, Wu J-Y (1982a) Taurine in the mammalian cerebellum demonstration by autoradiography with tritiated taurine and immunocytochemistry with antibodies against the taurine synthesizing enzyme, cysteine sulfinic acid decarboxylase. Proc. Natl. Acad. Sci. USA, 79, 2695-2699. 

Magnusson KR, Madl JE, Clements JR, Wu J-Y, Larsson AA, Beitz, AJ (1988) Colocalization of taurine-and cysteine sulfinic acid decarboxylase-like immunoreactivity in the cerebellum of the rat with monoclonal antibodies against taurine. J. Neurosci.. 8, 4551 564. 

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