Taurine degradation

Ruff J, K Denger, AM Cook (2003) Sulphoacetaldehyde acetyltransferase yields acetyl phosphate purification from Alcaligenes defragrans and gene clusters in taurine degradation. Biochem J 369 275-285. 

Taurine is degraded aerobically either by a 2-ketoglntarate-dependent dioxygenation to aminoacetaldehyde (Kertesz 1999) (cf. degradation of 2,4-dichlorophenoxyacetate) or by transamination and fission by a lyase that is also nsed anaerobically with the formation of acetate (Cook et al. 1999). 

Taurine (H3N CH2CH2S03 ) is formed as a product of cysteine catabolism and also arises from the oxidation of cyste-amine, which is produced during coenzyme-A degradation. It was given the name taurine because it was first isolated from the bile of the ox, Bos taurus. 

Taurine deficiency is rare in adult humans but is common in domestic cats, due to poor absorption from tinned catfood. Consequences of taurine deficiency in cats are cardiomyopathy, retinal degradation, reproductive failure in females, developmental abnormalities and impairment of the immune system. It is possible that a chronic deficiency in humans may have similar effects. 

Plasma should be separated from the blood cells within a few hours. For most amino acids the levels in plasma and red cells are comparable, but glutamate, aspartate, and taurine have extremely high intracellular levels and thus tend to rise in plasma upon hemolysis. A second effect of red cell degradation is the liberation of the enzyme arginase, which will convert arginine into ornithine. 

The chromatogram of free BA standard mixture is reported in Fig. 5.4.7. The Br-AMN degradation products are eluted at lower retention times than derivatised BA, close to the solvent front, so they do not impair BA separation. Free BA fraction also encloses taurine conjugates, previously enzymatically hydrolysed. The separation of glycine conjugated BA is illustrated in Fig. 5.4.8. In both chromatograms, the peaks of BA naphthacyl esters are fully resolved and separated from the reagent peaks. 

Although cystamine has been reported to be a product of the physiological degradation of CoA (47) and a precursor of taurine (48), its presence in mammalian liver has not been adequately established, and... 

Sulfite oxidase catalyzes one of the final stops in the oxidation of the sulfur amino acids. The catabolism of methionine can result in the appearance of its sulfur atom in cysteine, as shown in Chapter 8. Cysteine can be oxidized to cysteine sulfonate, as shciwn in the section on taurine in Chapter 2, and then degraded to pyruvate. Daily, an average of 25 mmol of sulfite is produced in the body. This amount is large compared with the dally intake of fo< sulfite, which is about 2.5 mmol- The point at which sulfite oxidase occurs in the cysteine catabolic pathway is shown in Figure 10,53, Sulfate (SO ") is required for the synthesis of su I fated polypeptides and polysaccharides. It is thought that sulfate is not required in the dict-... 

The in vivo mechanism of 35S-taurine formation from 35S-cysteine in the rat has been studied by Awapara and Wingo148. Ten minutes after injection, large amounts of 35S cysteine and traces of sulphate-35S were found only in the liver. After 20 minutes small amounts of 2-aminoethanesulphinic-3 5 S acid were also found (equation 81). Taurine began to appear in the liver 30 minutes after the injection. Two hours after administration, analyses for [35S]taurine, alanine, [35S]cysteic acid and 2-aminoethanesulphinic acid were carried out in liver, kidney, heart and spleen of the rats. [3 5S]Cysteic acid had been detected only when large amounts of 35S-labelled cysteine were injected. It has been suggested that the degradation of [35S]cysteine in vivo proceeds in rats according to equation 81. Formation of 2-aminoethanesulphinic acid and its oxidation to taurine is a preferred pathway. Much less [35S]sulphate than 2-aminoethanesulphinic-35S acid and taurine-35S had been found one hour after incorporation of 35S-labelled cysteine. 

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. 

Homocysteine metabolism involves three key enzymes methionine synthase, betaine homocysteine methyl transferase (BHMT) and cystathione p-synthase. Both vitamin B12 and folate are required in the methylation of homocysteine to methionine via metheonine synthase after donation of a methyl group from SAM during the methylation process. Homocysteine is also methylated by betaine in a reaction catalysed by BHMT and does not involve vitamin B12 and folate. The other metabolic fate for homocysteine is the transsulfuration pathway which degrades homocysteine to cysteine and taurine, and is catalysed by cystathione p-synthase with vitamin Bg as coenzyme. 

This gradient system has been adapted for the analysis of coastal tind interstitial waters where compounds derived from amino acid degradation such as P-alaavae, taurine or amino butyric acids may occur in addition to the standard amino acids given in Table 26-1. For less complex samples such as, e.g., hydrolysates the gradient run time may be abbreviated and a linear gradient employed. It should, however, be noted that under these conditions glycine and threonine are usually not separated. 

One of the pathways for the removal of cholesterol from the blood is by degradation to bile acids (Gordon et al., 1957 Lewis, 1958). A deficiency of the sulfur amino acids can be important in limiting the production of taurine, which is required for the formation of taurocholic acid (Filios and Mann, 1954). 

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

The metabolic pathways discussed above were based on experiments performed on adult animals. It was recently shown that tissues of chick and calf embryo exhibit certain peculiarities of sulfur metabolism which distinguish them from tissues of adult animals. Chapeville and Fromageot (36) observed that chick embryos in vivo rapidly utilize the S of SOs for the formation of taurine. It was shown that in the embryo hypotaurine is not a precursor of taurine and only yields traces of S04, while cysteate is rapidly decarboxylated to taurine. This pathway differs from that of adult animals where hypotaurine is readily degraded to SO4 (36). Further work of Chapeville et al. (37) suggests that the enzymic mechanism of this process in the embryo is compatible with the following reactions ... 

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