The synthesis of taurine from sulfate. VIII. A constitutive enzyme in mammals

Molecular characterization and taurine regulation of two novel CDOs (CDO1 and CDO2) from Carassius auratus

Cysteine oxygenase (CDO) is a mononuclear nonhemoglobin enzyme that catalyzes the production of taurine through the cysteine (Cys) pathway and plays a key role in the biosynthesis of taurine in mammals. However, the function of CDOs in bony fish remains poorly understood. In this study, we cloned CDO genes (CaCDO1 and CaCDO2) from Carassius auratus. The cDNA sequences of both CaCDO1 and CaCDO2 encoded putative proteins with 201 amino acids, which included structural features typical of the CDO protein family. Multiple sequence alignment and phylogenetic analysis showed that CaCDO1 and CaCDO2 shared high sequence identities and similarities with C. carpio homologs. Quantitative real-time polymerase chain reaction (qRT-PCR) results revealed that CaCDO1 and CaCDO2 were both broadly expressed in all selected tissues and developmental stages in C. auratus but had differing mRNA levels. In addition, compared to those of the taurine-free group, the in vivo mRNA expression levels of both CaCDO1 and CaCDO2 significantly decreased with increasing dietary taurine levels from 1.0 to 9.0 g/kg. Furthermore, in vitro taurine treatments showed similar inhibitory effects on the expression of CaCDO1 and CaCDO2 in the intestines of C. auratus. Our results also showed that the mRNA expression of CaCDO2 in the intestines was higher than that of CaCDO1 in response to in vivo and in vitro taurine supplementation. Overall, these data may provide new insights into the regulation of fish CDO expression and provide valuable knowledge for improving dietary formulas in aquaculture.

Taurine in development and nutrition

Taurine is an amino acid that is widely distributed in the fluids and tissues of man. In mammals, taurine is a major end-product of methionine metabolism. Taurine is found in most mammalian tissues but is only present in trace amounts in many plants. During fetal development of the brain in man and other mammals taurine is present in high concentrations and declines to lower, adult concentrations during neonatal life. However, during this time there is a net accumulation of taurine when the amount per brain rather than per gram of tissue is calculated. In man, taurine is apparently an essential nutrient, unlike in other animals which have a much greater capacity to synthesize this compound. The human infant, is particular, needs a dietary supply of taurine to synthesize the bile salt taurocholate. Thus, taurine appears to be an important component of the developing brain and must be supplied to man in the diet.

Comparative species utilization and toxicity of sulfur amino acids

Animal studies have shown that several methionine (Met) and cysteine (Cys) analogs or precursors have L-Met- and L-Cys-sparing activity. Relative oral bioavailability (RBV) values, with the L-isomer of Met and Cys set at 100% (isosulfurous basis), are near 100% for D-Met for animals but only about 30% for humans. Both the OH and keto analogs of Met have high RBV-sparing values, as does N-acetyl-L-Met (the D-isomer of acetylated Met has no bioactivity). L-Homocysteine has an RBV value of about 65% for Met sparing in rats and chicks, but D-homocysteine has little if any Met-sparing activity. S-Methyl-L-Met can partially spare Met, but only when fed under dietary conditions of choline/betaine deficiency. Relative to L-Cys, high RBV values exist for L-cystine, N-acetyl-L-Cys, L-homocysteine, L-Met, and glutathione, but D-cystine, the keto analog of Cys, L-cysteic acid, and taurine have no Cys-sparing activity. l-2-Oxothiazolidine-4-carboxylate has an RBV value of 75%, D-homocysteine 70%, and DL-lanthionine 35% as Cys precursors. Under dietary conditions of Cys deficiency and very low inorganic sulfate (SO4) ingestion, dietary SO4 supplementation has been shown to reduce the Cys requirement of several animal species as well as humans. Excessive ingestion of Met, Cys, or cystine has also been studied extensively in experimental animals, and these sulfur amino acids (SAA) are well established as being among the most toxic of all amino acids that have been studied. Even though Cys and its oxidized product (cystine) are equally efficacious at levels at or below their dietary requirements for maximal growth, Cys is far more toxic than cystine when administered orally in the pharmacologic dosing range. Isosulfurous (excess) levels of cystine, N-acetyl-L-Cys, or glutathione are far less growth depressing than L-Cys when 6 to 10 times the minimally required level of these SAA compounds are fed to chicks.

Effects of ageing on the content in sulfur-containing amino acids in rat brain

Concentrations of the sulfur-containing amino acids methionine, homocysteic acid, cysteic acid and taurine were measured in brain structures of young and old Wistar rats in an attempt to establish a possible link between the increase in oxidative stress with ageing and changes in tissue levels of these amino acids. Contrary to data reported by others, in all brain structures of young and old rats homocysteic acid levels could not be quantified. Compared with young rats, in old animals taurine and methionine concentrations significantly decreased in striatum and cortex; decreased taurine levels were also found in nucleus accumbens and cerebellum and lower concentrations of methionine were found in midbrain, hippocampus and pons-medulla. Cysteic acid levels either did not change or significantly increased in cortex and hippocampus. These results are discussed taking into account the biosynthesis of sulfur-containing amino acids in rat brain and the decrease in glutathione in relation to oxidative stress with ageing. Changes in aspartic acid, glutamic acid, serine, glutamine, glycine and GABA concentrations with ageing were also determined in the same brain structures and were in good agreement with those previously reported (Strolin Benedetti et al., 1990 a, b).

Biological availability to the rat of intrinsic and extrinsic iron with soybean protein isolates

Evaluations were conducted to assess the biological availability of iron in three food grade isolated soybean proteins and to evanuate the influence of these proteins on iron added to the diet from a source of known high biological availability. Ferrous sulfate was used as the standard iron source in all experiments. The biological availability was measured by a 14-day hemoglobin repletion after a 4 week depletion period using multiple dose response and comparing the test samples and standard iron source by the slope ratio assay procedure. The relative iron bioavailability for three isolated soybean proteins was A = 60%; B = 64% and C = 59% with a mean value of 61%. Autoclaving isolated soybean protein B at 108.4 degrees improved iron bioavailability over the unheated samples while isolated soybean protein A was unaffected by this treatment. Iron added to the diets containing isolated soybean protein had bioavailabilities similar to that of iron present in the soybean which supports the common dietary iron pool hypothesis. The high iron content (0.18 mg/g protein) coupled with the bioavailability data make the isolated soybean proteins a good dietary iron source.