Metabolic Functions of Taurine

R. Huxtable, Metabolism and function of taurine in the heart, in "Taurine, R. Huxtable and A. Barbeau, eds.. Raven Press,... 

Huxtable,R."Metabolism and function of taurine in the heart"in"Taurine"Huxtable,R.and Barbeau,A.ed.Raven Press,New York(1976). 

In addition to the established vitamins, a number of organic compounds have clear metabolic functions they can be synthesized in the body, but it is possible that under some circumstances (as in premature infants and patients maintained on long-term total parenteral nutrition) endogenous synthesis may not be adequate to meet requirements. These compounds include biopterin (Section 10.4), carnitine (Section 14.1), choline (Section 14.2), creatine (Section 14.3), inositol (Section 14.4), molybdopterin (Section 10.5), taurine (Section 14.5), and ubiquinone (Section 14.6). 

Taurine is not an exclusive constituent of nervous tissue it is also present at very high levels in contractile and secretory tissues. Since, except for the synthesis of taurocholic acid, taurine does not participate in metabolic reactions, its occurrence in animal tissues at substantial amounts should be related with a specific function which remains still unknown. If we consider that most taurine in nervous system is not related with a function as a neurotransmitter, the possibility that a single role is played by taurine in nervous, contractile or secretory tissues may be raised. Evidently, a multiplicity of taurine roles may also be envisaged, but we rather favour the hypothesis of a single action, probably at a basic mechanism underlying contractile, secretory and nervous function. A common denominator in all these functions is a modification of calcium gradients related to the excitation state of the tissue and a subsequent redistribution of calcium in order to return towards the resting intracellular levels. Taurine... 

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). 

Taurine was discovered in 1827 in ox hUe, where it is conjugated with the bile acids. It was later shown to be a major excretory product of the sulfur amino acids methionine and cysteine. Until about 1976, it was assumed that it was a metabolic end-product whose only function was the conjugation of bile acids. In the rat, taurine synthesis accounts for 70% to 85% of total cysteine catabolism. 

Conjugation with amino acids is an important route of Phase 2 metabolism for xenobiotics containing a carboxylic acid functional group. The amino acids involved include glycine, glutamine and taurine (an aminosulfonic... 

Amino acids are involved in many metabolic processes and m protein synthesis. In the central nervous system, they also function as neurotransmitters or neuromodulators (Davidson, 1976 Corradetti et al., 1983 Fonnum, 1981, 1984). Numerous studies have demonstrated the excitatory effects of aspartate and glutamate (Watkins and Evans, 1981) the inhibitory effects of glycine, y-aminobutyric acid (GABA), and taurine (Schaffer et al., 1981 Lloyd et al., 1983 Roberts, 1984), and the precursor roles of tryptophan in serotonin synthesis and of tyrosine and phenylalanine in the biosyntheses of catecholamines (Sved, 1983). It is not surprising, therefore, to see an ever-increasing interest in amino acid analysis in biological samples. 

Speculation has ascribed several functions to salivary thiocyanate a) an oral antiseptic, (6) an activator of ptyalin, (c) a form in which —CN compounds are eliminated, [d) a by-product of sulphur metabolism, possibly related to the taurine of bile. 

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