Brain taurine concentration

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... 

Glutamate is the main excitatory amino acid neurotransmitter in central and peripheral nervous systems. Its concentration in brain is higher than in other body tissues. In the brain, the concentration of glutamate is 3- to 4-fold greater than that of aspartate, taurine, or glutamine (McGeer et al., 1987). The most abundant amino acid... 

Taurine - A glyclne-like, sulphur containing amino acid, taurine (12) is found in reasonably high concentrations throughout the mammalian central nervous system and in heart.In brain, taurine is formed as a result of the decarboxylation of cysteine sulphinic acid (15) to hypotau-rlne (8 ), which in turn is oxidized to form taurine.Like other transmitter candidates, taurine is accumulated and released by brain tissue and the accumulation can be inhibited by ouabain. Clinically, significant alterations in taurine levels may be associated with retinitis pigmentosa, epilepsy, mongolism, and possibly heart disease. 

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). 

Some further generalities can be made from data in this table. Except for octane with its known CNS depressant actions, no other compound appeared in significant quantities in the brain. The herbicides were the only compounds which occurred in significant concentrations in the bile and this has been shown (32) to be mainly metabolites, i.e., the taurine conjugates of 2,4-D and 2,4,5-T. Also the kidney and urine samples contained large concentrations of these same herbicides as did those from fish treated with octane or DEHP. Presumably these latter values are at least in part metabolities. Due to its large mass (ca. 

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 essentiality of cysteine for the fetus and newborn may underlie their low or nonexistent ability to convert cysteine to taurine, another low molecular weight sulfur containing confound apparently required in large amounts by developing brain (Sturman et al., 1978). The supply of cysteine may all be required for protein synthesis and none spared for taurine formation. Cystelnesulflnic acid decarboxylase (EC 4.1.1.12), the enzyme chiefly responsible for taurine biosynthesis in mammals, develops slowly after birth and reaches maximum activity in mature brain (Agrawal et al.,1971 Pasantes-Morales et al.,1976 Rassin et al., 1979), although the concentration of taurine decreases over this same period (Fig. 4). Cystelnesulflnic acid decarboxylase also uses pyridoxal 5 -phosphate as coenzyme, and is extremely sensitive to a dietary deficiency of vitamin Bg (Hope, 1955 Rassin and Sturman, 1975). 

Fig. 4. Concentration of taurine in rhesus monkey brain during development. From Sturman and Gaull,1975.

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