Taurine function

Low levels of hypochlorous acid can function as a mediator in cell activation, induce NFKB heterodimer p50 /p65 in a T-lymphocytic cell line through proteolysis of IKB and pl05 inhibitors. Hypochlorous acid will also contribute to the release of TNFo in cellular supernatants of T-lymphocytes which are capable of commencing activation in non-induced cells (Schoonbroodt et ah, 1997). Hypochlorous acid can react with amines to produce chloroamines and N-chlorinated derivatives that have a long lifetime in plasma. Taurine, a sulfonated amino acid, will finally combine with these two products to reduce their toxicity. 

Miller, J. W Kleven, D. T., Domin, B. A., and Fremau Jr., R. T. (1997) Cloned sodium-land chloride-) dependent high affinity transporters for GABA, glycine, proline, betaine, taurine, and creatine, in Neurotransmitter Transporters Structure, Function, and Regulation (Reith, M. E. A., ed.). Humana Press, Totowa, NJ, pp. 101-150. 

M. Tomi, T. Terayama, T. Isobe, F. Egami, A. Morito, M. Kurachi, S. Ohtsuki, Y. S. Kang, T. Terasaki, and K. Hosoya. Function and regulation of taurine transport at the inner blood-retinal barrier. Microvasc. Res. 73 100-106 (2007). 

The high concentration of taurine in cells is an indication that it is an important molecule but not all functions or their importance are known. Cell membranes are impermeable to taurine so that it must be formed in the cell, within which its concentration is very high. The concentration ratio across the membrane is also very high in cells in the retina (400), neurones in the brain (500) and in some tumour cells (7000). Unfortunately, the precise role of taurine in these particular cells is not known. Of the many functions that are known (Huxtable, 1992 Schuller-Levis Park, 2003) the following is a summary ... 

The maintenance of the structure and function of photoreceptors in the eye depends on taurine. As an antioxidant, it may protect the cell membranes in the retina. 

It is an ideal compound for regulation of osmotic pressure, since it has a low molecular mass, is highly soluble and has no net charge. It serves this function in some of the tissues of elasmobranch fish such as the skate and shark, and in marine invertebrates. Any damage to these tissues releases taurine, which is used as a chemoattractant for predators such as the shrimp, which wiU attack small fish. 

Deficiency of this coenzyme can lead to many manifestations. Clinical signs include retarded growth, acrodynia, alopecia, skeletal changes and anemia, while changes in neurotransmitters, such as dopamine, serotonin, norepinephrine (noradrenaline), tryptamine, tyramine, histamine, y-aminobutyric acid, and taurine, affect the brain function and can lead to seizures and convulsions. An overdose of vitamin Bg leads to neuronal damage and sensory and motor effects [417],... 

Age does not have a major influence on amino acid levels, with exception of the neonatal period. Premature babies may have underdeveloped hepatic and renal function, leading to increased tyrosine and methionine in their plasma as well as enhanced urinary losses of cystine, lysine, glycine, proline, hydroxyproline, and cystathionine. Taurine levels are generally increased in the first days of life. 

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... 

Other neurotransmitters. The abundant glutamate, GABA, and glycine are major neurotransmitters. Do other amino acids also function in the brain Roles for L-aspartate and D-serine (p. 1785) have been identified, but it is very difficult either to discover or to disprove a neurotransmitter function for other amino acids. It is even more difficult for small amounts of various amines and small peptides that are present in the brain. Taurine (Fig. 24-25) is one of the most abundant free amino acids in animals and meets several criteria for consideration as both an inhibitory and an excitatory transmitter.797 798 However, its function is still uncertain (see Chapter 24). Homocysteic acid, formed by oxidation of homocysteine, is a powerful neuroexcitatory substance, but its concentration in the brain is very low.149 d-Aspartate is also present... 

The taurine residue can also be found as an amide derivative of the 26-carboxylic acid function in the 3p,5a,6p,15a-polyhydroxylated steroids 328 and 329, which were obtained from the starfish Myxoderma platyacanthum [245]. The structures of both compounds were determined from spectral data and chemical correlations. The bile of the sunfish Mola mola has been shown to contain a new bile acid conjugated with taurine (330) together with sodium taurocholate. Compound 330 was identified as sodium 2-[3a,7a, 11 a-trihydroxy-24-oxo-5P-cholan-24-yl]amino]ethane-sulfonate on the basis of its physicochemical data and chemical transformations [246]. 

Grafe, E, Wohlrab, W., Neubert, R.H. etal. Functional characterization of sodium- and chloride-dependent taurine transport in human keratinocytes. Eur. J. Pharm. Biopharm. 2004 57 337—41. 

Ramamoorthy, S., Kulanthaivel, P., Leibach, F.H., Mahesh, V.B., Ganapathy, V. (1993). Solubilization and functional reconstitution of the human placental taurine transporter. Biochim. Biophys. Acta 1145,250-256. 

The most abundant amino add in the human organism does not occur in proteins and does not have a carboxyl group. Its addic residue is the sulfonate group, and its name is taurine (N+H3-CH2-CH2-S03 ). It occurs in the free state (exact function often unknown) and in bile salts, in which it plays an important role in fat digestion and absorption (see Chapters 9 and 19). Other amino acids that do not occur in proteins are ornithine and citrulline. They are important intermediates in the urea cycle described in Chapter 20. 

As already pointed out, cysteine may be metabolized to pyruvate, or it can be oxidized to cystine. It can also be converted to taurine, NH3+-CH2-CH2-S03. Taurine is obtained by oxidizing the -SH group of cysteine and losing the carboxyl group of decarboxylation. Taurine is quite abundant in most tissues and is said to be the most abundant "amino acid" of the human organism. One of its functions is to conjugate primary bile acids (Chapter 19). 

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