Biosynthesis of Taurine

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

Oxidation to cysteic acid, followed hy decarhoxylation to taurine. Cysteic acid and cysteine sulfinic acid decarboxylase activities occur in constEint ratio in veuious tissues, and it is iikeiy that hoth substrates are decarboxy-lated by the same enzyme. In genereil, cysteine sulfinic acid is the preferred substrate, emd there is little formation of taurine byway of cysteic acid. 

S-Oxidation of cysteeunine released by the catabolism of pantothenic acid (Section 12.2.2) or formed by the decarboxylation of cysteine. 

In the liver cind brain, the main pathway is by way of cysteine sulfinic acid, wherccis in tissues with low cysteine sulfinic acid decarboxylase activity the mciin precursor of taurine is cystccunine. 

The central nervous system has at least three enzymes capable of decar-hoxylating cysteine sulfonic acid, one of which is glutamate deccnhoxylase. Glutamate and cysteine sulfinic acid are mutually competitive. In some hrain regions, more than half the total cysteine sulfinic acid decarhoxylcise activity may he from glutamate decarboxylase. 

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HO g Ss C02H 0 NH2 Occurs in mammalian tissues Cysteine sulfinic acid - intermediate in the biosynthesis of taurine (taurine is essential for many biological processes) 13... 

Scheme 2.2 Examples of reactions catalyzed by and RNA by the protein AlkB [54] (R = sugar al

Tests to determine the nature of the compounds formed from the decarboxylation of cystine that could undergo oxidation led to the observation that cystamine disulfoxide was oxidized with ease, whereas cystamine was completely resistant. From these observations, it was hypothesized that two oxidizing enzymes may be involved in the reaction, one oxidizing cystine to the disulfoxide, and one continuing the oxidation of the cystamine disulfoxide subsequent to the decarboxylation of the cystine disulfoxide. If it is assumed that the cystamine disulfoxide is simultaneously oxidized and cleaved to 2-aminoethanesulfinic acid, the oxidation scheme leads to the intermediate that was established for the biosynthesis of taurine from cysteine by Awapara. ... 

S.S. Oja, M.L. Karvonen and P. Lahdesmaki, Biosynthesis of Taurine and Enhancement of Decarboxylation of Cysteine Sulphinate and Glutamate by the Electrical Stimulation of Rat Brain Slices, Brain. Res. 55 173 (1973). 

Oja, S. S., Karvonen, M.-L., and Lahdesmaki, P., 1973, Biosynthesis of taurine and enhancement of decarboxylation of cysteine sulphinate and glutamate by the electrical stimulation of rat brain slices. Brain Res., 55 173. 

We have investigated the effects of adrenergic stress on the transport and biosynthesis of taurine in the heart, in order to ascertain the origin of the increased taurine content in congestive failure. 

Fig. 2. Biosynthesis of taurine during isoproterenol-induced hypertrophy. Conditions as fig. 1. Symbols Squares indicate conversion of cys-...

Table 2. Effect of Dietary Taurine on the Transport and Biosynthesis of Taurine in the Heart.

Fig. 7 Biosynthesis of NATs and TRP channel activation by NATs. (a) Evidence for a fatty acyl CoA taurine A-acyltransferase activity was detected in mouse tissue by incubating taurine and arachidonoyl-CoA with various tissue lysates, (b) arachidonyl NAT was tested as an activator of the TRPV1 (black line), TRPV4 (gray line), and TRPM8 (dashed line) ion channels. Channel activation was measured using a Fura-2-based calcium-imaging assay, where the ratio between the fluorescence at 340 and 380 nm is reflective of cellular calcium concentrations...

Biosynthesis of the two primary bile acids is followed by conjugation of their carboxylic group with the amino group of either glycine or taurine, mediated by a cytoplasmic enzyme. By means of this conjugation, the primary bile acids, which initially are barely water-soluble, become anions and are thus rendered hydrophilic. In this way four conjugated bile acids are formed ... 

Alternatively, R-cysteine is utilized for the biosynthesis of cosubstrates for several conjugation reactions, such as glutathione, sulfate (PAPS), and taurine. The unphysiological isomer S-cysteine has been used to investigate the mechanistic aspects of physiological processes involving cysteine. In rats, the sulfoxidation rates of R- and S-cysteine, as well as the sulfation rates of the test substrate harmol sulfate, were found to be very similar, so that stereoselectivity for the amino acid does not seem to play a role in these reactions (Glazenburg et al., 1984). Since S-cysteine, in contrast to the R-isomer, did not increase the taurine concentration in serum, this type of stereoselectivity can be used to selectively enhance sulfate availability in vivo. 

Biochemical studies with isolated rat hepatocytes have largely been concerned with transport mechanisms [15], secretion of bile acids [17-19], or biosynthesis of bile acids [20]. The capacity of cultured hepatocytes to convert tauro- or glyco-chenodeoxycholate to a- and )8-muricholates [19,21] and to produce bile salts (glycine or taurine conjugates) during the dark phase of the diurnal cycle [21] has been established. Demonstrations of other metabolic transformations by hepatocytes are included in the following sections. 

The more complex sulphur requirements of the marine animals are met largely by cysteine, cystine, methionine, biotin, and thiamine (Young and Maw, 1958) (Fig. 4). Cysteine is a component of the tripeptide glutathione and a precursor of taurine. Methionine is as an essential amino acid involved in biosynthesis of proteins, creatine and adrenaline. Adenosylmethionine is considered to be the active part in transmethylation, e.g. of choline. Methionine is part of the pathways to homocysteine, cystathionine and methylthioadenosine (Young and Maw, 1958). Various organisms convert cysteine and/or cystine into mercapturic acids, cysteine sulphinic acid, and thiazolidine derivatives (Zobell, 1963). 

The terminal step in the biosynthesis of bile acids from cholesterol is represented by the enzymatic synthesis of water-soluble bile acid conjugates of taurine and/or glycine through a peptide bond, as shown in Fig. 1. 

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). 

D. Cavallini, R. Scandurra, S. Duprg, S. Santoro and D. Barra, A New Pathway of Taurine Biosynthesis, Physiol. Chem. Phys. 8 157 (1976). 

In the present chapter we will report the subcellular distribution pattern of taurine and enzymatic activities involved in taurine biosynthesis in ox retina and in particular in the subcellular nuclear fraction which contains besides nuclei, the outer and inner segments of photoreceptors as well as pinched-off nerve-endings of the photoreceptors. 

G. Ricci, and D. Barra, Alternative pathways of taurine biosynthesis, ij2 "T aurine", R. Huxtable and A. Barbeau eds., Raven Press. New York (1976). 

The problem of regulation is complicated by the metabolic complexity of sulfur amino acids, and the wide variation in organ taurine concentrations between species. The major putative metabolic routes to taurine from cysteine are three These involve the intermediacy respectively of cysteine sulfinic acid, cysteic acid, and cysteamine. The first two utilize the enzyme cysteine sulfinic acid decarboxylase (CSAD), and the latter the enzyme cysteamine dioxygenase (CD). The distribution of these enzymes differ both quantitatively and qualitatively in corresponding organs of various species. Other pathways of taurine biosynthesis have also been proposed. For... 

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