Concentrations Of Sulfur-containing Amino Acids Research Articles

ANALYSIS OF THE RELATIONSHIP BETWEEN INDICATORS OF OXIDATIVE STRESS AND THE AMINO ACID PROFILE OF BLOOD PLASMA IN PSORIASIS

Introduction. Psoriasis is an autoimmune disease that affects the skin, has a number of systemic manifestations and is associated with the devel-opment of a number of somatic pathologies. Significant systemic metabolic features of psoriasis are changes in the pool of free amino acids and oxi-dative stress. The purpose of the study: analysis of markers of lipid peroxidation and oxidative modification of plasma proteins and peripheral mononuclear cells, the amino acid spectrum of blood plasma, in relation to each other and clinical signs of severity and duration of psoriasis, body mass index and blood pressure indicators. Material and methods. The study group included 45 patients with psoriasis vulgaris. The control group included 46 donors. Determination of the lev-els of products of lipid peroxidation and oxidative modification of proteins was carried out by spectrophotometric methods. Blood plasma amino acid levels were determined by capillary electrophoresis. Results. In patients with psoriasis, an increase in the concentrations of primary and secondary products of lipid peroxidation and the level of metal-catalyzed oxidative modification of proteins in blood plasma, a decrease in the concentrations of end products of lipid peroxidation in peripheral mono-nuclear cells were revealed. In the amino acid profile of the blood plasma of patients with psoriasis, an increase in the relative concentration of sulfur-containing amino acids, concentrations of phenylalanine, leucine, cysteine, and a decrease in the relative concentration of oxyaminoacids were re-vealed. Relationships between the levels of amino acids and markers of oxidative stress with the duration of the course of the disease or exacerbation, as well as the severity of psoriatic lesions of the skin, were not revealed. Cysteine levels in patients with psoriasis are positively correlated with body mass index and diastolic blood pressure; the relative content of oxyaminoacids in blood plasma negatively correlates with body mass index. Conclusions. Changes in the amino acid profile of blood plasma in psoriasis occur in parallel with oxidative stress and skin inflammation, but are as-sociated with excess body weight for cysteine and oxyaminoacids, which allows us to consider the levels of cysteine and oxyaminoacids as promising prognostic and diagnostic markers of comorbid pathology associated with psoriasis.

Changes in the concentration of sulfur-containing amino acids in the brain after methionine load in the experimentChanges in the concentration of sulfur-containing amino acids in the brain after methionine load in the experiment

The effect of methionine overload on the state of the pool of sulfur-containing amino acids and their metabolites was studied in the various brain structures determined by reverse phase high performance liquid chromatography (HPLC). In all regions of the brain studied, methionine led to a unidirectional imbalance of sulfur-containing compounds: there was an increase in the concentrations of methionine, cystathionine and hypotaurine. The most pronounced increase in methionine and hypotaurine levels was observed in the striatum, cystathionine in the hemispheres. A significant increase in taurine concentration was observed only in the hypothalamus and striatum. In other parts of the brain a tendency to increase its level was shown. In all brain regions studied except the striatum, serine levels were decreased. In the cerebellum, in comparison with other regions, an increase in the level of cysteic acid and a decrease in the level of cysteinesulfinic acid were observed, which indicates that taurine synthesis is occurred mainly through the cysteine sulfinate oxidation.

Metabolomic Analysis of Liver from Dietary Biotin Deficient Mice.

Biotin is a water-soluble B-complex vitamin that functions as a cofactor of five carboxylases. Because biotin-dependent carboxylases catalyze indispensable cellular metabolic functions, biotin deficiency is considered to be involved in various pathological conditions. Moreover, biotin supplementation shows pharmacological effects in vivo. However, the precise mechanisms by which biotin deficiency induces pathological conditions remain unclear. Although abnormal metabolites are used as indicators for biotin deficiency, few comprehensive analyses of total metabolites have been reported. In this study, we analyzed the metabolomic profiles of liver extracts prepared from biotin-sufficient (BS) and -deficient (BD) mice. Thirteen of 126 metabolites showed significantly different concentrations between liver extracts from BD and BS mice. The concentrations of 5 essential amino acids, Met, Val, Thr, Ile, and Leu, and 2 conditionally essential amino acids, Cys and Tyr were significantly lower in BD mice than in BS mice. Among these, the concentrations of sulfur-containing amino acids, Cys and Met, were more than 1.5-fold lower in BD mice. The concentrations of Met metabolites, such as S-adenosylmethionine and S-adenosylhomocysteine were not significantly different between the two groups. The concentrations of glutathione and its reaction intermediates γ-Glu-Cys tendency to be lower in BD mice. The present study revealed that biotin deficiency induces an abnormal amino acids composition, especially among sulfur-containing amino acids and provide important information on the effect of biotin as a pharmacological agent.

Concentration of sulfur-containing amino acids at turkey broilers during and after muscle dystrophy, fed with deficient feed supplemented with oxidised fat

Concentration of sulfur-containing amino acids at turkey broilers during and after muscle dystrophy, fed with deficient feed supplemented with oxidised fat

Identification and functional characterization of the sulfate transporter gene GmSULTR1;2b in soybean.

BackgroundSoybean is a major source of oil and protein in the human diet and in animal feed. However, as soybean is deficient in sulfur-containing amino acids, its nutritional value is limited. Increasing sulfate assimilation and utilization efficiency is a valuable approach to augment the concentration of sulfur-containing amino acids in soybean seeds, and sulfate transporters play important roles in both sulfate uptake and translocation within plants.ResultsIn this study, we isolated and characterized a soybean sulfate transporter gene: GmSULTR1;2b. The gene was found to be specifically expressed in root tissues and induced by low-sulfur stress. In addition, GmSULTR1;2b expression in yeast could complement deficiency in the sulfate transporter genes SUL1 and SUL2. Under +S conditions, GmSULTR1;2b-overexpressing tobacco plants accumulated higher levels of organic matter and exhibited enhanced biomass and seed weight compared to control plants. Under -S conditions, acclimation of GmSULTR1;2b-overexpressing plants was much better than control plants. GmSULTR1;2b-overexpressing tobacco seedlings showed better tolerance to drought stress than the control plants, but no significant difference was observed under salt stress. Transcriptome analysis revealed 515 genes with at least a 2-fold change in expression in the leaves of tobacco plants overexpressing GmSULTR1;2b. Of these, 227 gene annotations were classified into 12 functional categories associated with 123 relevant pathways, including biosynthesis and metabolism-related proteins, stress-related proteins, and transporters.ConclusionsThe findings reported here indicate that the increased biomass and seed yield observed in transgenic tobacco plants could have resulted from greater nutrient uptake and transport capability as well as enhanced development and accumulation of organic matter. Taken together, our results indicate that GmSULTR1;2b plays an important role in sulfur uptake and could alter the sulfur status of plants. Our study suggests that overexpressing GmSULTR1;2b may enhance plant yield under +S conditions, reduce plant production loss under -S conditions, and improve plant tolerance to sulfur deficiency stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2705-3) contains supplementary material, which is available to authorized users.

Introgression of leginsulin, a cysteine-rich protein, and high-protein trait from an Asian soybean plant introduction genotype into a North American experimental soybean line.

Soybean is an important protein source for both humans and animals. However, soybean proteins are relatively poor in the sulfur-containing amino acids, cysteine and methionine. Improving the content of endogenous proteins rich in sulfur-containing amino acids could enhance the nutritive value of soybean meal. Leginsulin, a cysteine-rich peptide, predominantly accumulates in Asian soybean accessions but not in most North American cultivars. By screening diverse soybean accessions from the USDA Soybean Germplasm Collection, we were able to identify one plant introduction, PI 427138, as a high-protein line with relatively high amounts of both elemental sulfur and leginsulin. We introgressed these desirable traits from PI 427138 into an experimental line with the aim of improving the overall protein content and quality of seed proteins. Biochemical characterization of inbred progenies from the cross of LD00-3309 with PI 427138 grown at six locations revealed stable ingression of high protein, high elemental sulfur, and high leginsulin accumulation. Comparison of soybean seed proteins resolved by high-resolution 2-D gel electrophoresis in combination with Delta2D image analysis software revealed preferential accumulation of a few glycinin subunits contributed to the increased protein content in the introgressed lines. Amino acid analysis revealed that even though the leginsulin introgressed lines had higher protein, leginsulin, and elemental sulfur, the overall concentration of sulfur-containing amino acids was not significantly altered when compared with the parental lines. The experimental soybean lines developed during this study (Leg-3, Leg-7, and Leg-8) lack A5, A4, and B3 glycinin subunits and could be utilized in breeding programs to develop high-quality tofu cultivars.

The gentio-oligosaccharide gentiobiose functions in the modulation of bud dormancy in the herbaceous perennial Gentiana.

Bud dormancy is an adaptive strategy that perennials use to survive unfavorable conditions. Gentians (Gentiana), popular alpine flowers and ornamentals, produce overwintering buds (OWBs) that can persist through the winter, but the mechanisms regulating dormancy are currently unclear. In this study, we conducted targeted metabolome analysis to obtain clues about the metabolic mechanisms involved in regulating OWB dormancy. Multivariate analysis of metabolite profiles revealed metabolite patterns characteristic of dormant states. The concentrations of gentiobiose [β-D-Glcp-(1→6)-D-Glc] and gentianose [β-D-Glcp-(1→6)-D-Glc-(1→2)-d-Fru] significantly varied depending on the stage of OWB dormancy, and the gentiobiose concentration increased prior to budbreak. Both activation of invertase and inactivation of β-glucosidase resulted in gentiobiose accumulation in ecodormant OWBs, suggesting that gentiobiose is seldom used as an energy source but is involved in signaling pathways. Furthermore, treatment with exogenous gentiobiose induced budbreak in OWBs cultured in vitro, with increased concentrations of sulfur-containing amino acids, GSH, and ascorbate (AsA), as well as increased expression levels of the corresponding genes. Inhibition of GSH synthesis suppressed gentiobiose-induced budbreak accompanied by decreases in GSH and AsA concentrations and redox status. These results indicate that gentiobiose, a rare disaccharide, acts as a signal for dormancy release of gentian OWBs through the AsA-GSH cycle.

Statistical analysis of sake-preparation conditions and dimethyl trisulfide formation

Dimethyl trisulfide (DMTS) is known to be responsible for hineka, an off-flavor that develops during storage, in sake. Previous studies have attempted to elucidate the mechanism of DMTS formation during sake storage, but the mechanism underlying DMTS formation remains unclear. In this study, we determined the sake-preparation conditions that affect DMTS formation. We analyzed 76 sake samples immediately after filtration, which were donated by sake-producing companies. We measured the DMTS concentration in sake after 7 days of storage at 70°C (DMTS-pp) using gas chromatography/mass spectrometry. In the statistical analysis, DMTS-pp was set as the objective variable, whereas the preparation conditions and analytical results for sake were set as the explanatory variables. We used multiple linear regression (MLR) analysis with a stepwise method and partial least squares regression (PLSR) to analyze the data. The statistical analysis showed that the significant factors for DMTS-pp were the average temperature in the moromi mash (Temp ave), the total daily temperature in the moromi mash (Temp sum), the concentration of sulfur-containing amino acids in sake, and the Zn concentration in sake. These factors explained 63.4% of the variance in DMTS-pp according to the MLR analysis and 64.2% according to the PLSR analysis. Further MLR analysis showed that Temp ave in early stage and Temp sum in later stage were important factors for DMTS-pp. This result suggests that the rice dissolution caused by high Temp ave in early stage and yeast cell lysis caused by high Temp sum in later stage contribute to high DMTS-pp.

Transgenic soybean plants overexpressing O-acetylserine sulfhydrylase accumulate enhanced levels of cysteine and Bowman–Birk protease inhibitor in seeds

Soybeans provide an excellent source of protein in animal feed. Soybean protein quality can be enhanced by increasing the concentration of sulfur-containing amino acids. Previous attempts to increase the concentration of sulfur-containing amino acids through the expression of heterologous proteins have met with limited success. Here, we report a successful strategy to increase the cysteine content of soybean seed through the overexpression of a key sulfur assimilatory enzyme. We have generated several transgenic soybean plants that overexpress a cytosolic isoform of O-acetylserine sulfhydrylase (OASS). These transgenic soybean plants exhibit a four- to tenfold increase in OASS activity when compared with non-transformed wild-type. The OASS activity in the transgenic soybeans was significantly higher at all the stages of seed development. Unlike the non-transformed soybean plants, there was no marked decrease in the OASS activity even at later stages of seed development. Overexpression of cytosolic OASS resulted in a 58-74% increase in protein-bound cysteine levels compared with non-transformed wild-type soybean seeds. A 22-32% increase in the free cysteine levels was also observed in transgenic soybeans overexpressing OASS. Furthermore, these transgenic soybean plants showed a marked increase in the accumulation of Bowman-Birk protease inhibitor, a cysteine-rich protein. The overall increase in soybean total cysteine content (both free and protein-bound) satisfies the recommended levels required for the optimal growth of monogastric animals.

Exogenous hydrogen sulfide (H2S) protects against regional myocardial ischemia–reperfusion injury

Hydrogen sulfide (H2S) is a gaseous mediator, produced by the metabolic pathways that regulate tissue concentrations of sulfur-containing amino acids. Recent studies indicate that endogenous or exogenous H2S exerts physiological effects in the cardiovascular system of vertebrates, possibly through modulation of K ATP channel opening. The present study was undertaken to examine the hypothesis that H2S is cytoprotective against myocardial ischemia-reperfusion injury and that this protective action is mediated by K ATP opening. Rat isolated hearts were Langendorff-perfused and underwent 30 min left main coronary artery occlusion and 120 min reperfusion. The resulting injury was assessed as infarct size, determined by tetrazolium staining. Treatment of hearts with the H2S-donor, NaHS, commencing 10 min prior to the onset of coronary occlusion and maintained until 10 min reperfusion, resulted in a concentration-dependent limitation of infarct size (control, 41.0 +/- 2.6% of risk zone; NaHS 0.1 microM, 33.9 +/- 2.1%, [0.05 > P < 0.1]; NaHS 1 microM, 20.2 +/- 2.1% [P < 0.01]). Pretreatment with the K ATP channel blockers glibenclamide 10 microM or sodium 5-hydroxydecanoate (5HD) 100 microM led to abrogation of the infarct-limiting effect of NaHS 1 microM (glibenclamide + NaHS 42.5 +/- 3.6%; 5HD + NaHS 44.7 +/- 2.2%). No statistically significant effects of NaHS treatment on coronary flow, heart rate or left ventricular developed pressure were observed in this experimental preparation. These data provide the first evidence that exogenous H2S protects against irreversible ischemia-reperfusion injury in myocardium and support the involvement of K ATP opening in the mechanism of action. Further work is required to elucidate the potential role of endogenous H2S as a cytoprotective mediator against myocardial ischemia-reperfusion injury, the mechanisms regulating its generation, and the nature of its interaction with protein targets such as the K ATP channel.

Genetic engineering to improve quality, productivity and value of crops

Over the next 25 years, we believe that the most significant changes in crops will come about by applying genetic engineering tools. Crops may be bioengineered to produce modified kinds of starch, oils and high-value proteins for better nutrition, medical diagnostics and industrial uses. For example, walnuts and peanuts containing healthier oils, along with oxidative stability, could become available to consumers. Seedless vegetables and other fruits should appear in the marketplace within 10 years. Oil-producing seed crops may be modified to create specialty oils for a variety of nonfood products such as detergents, lubricants, inks and dyes. Feed seeds engineered to produce higher concentrations of sulfur-containing amino acids could improve wool growth in sheep. Plants could be modified to deliver oral vaccines that prevent diseases such as hepatitis and influenza. Strawberries are being targeted by genetic engineering to extend their shelf life, and within 25 years fields may be planted with varieties that allow farmers to control the timing of fruit production. Although currently controversial, we believe genetic engineering will prove to be invaluable to the future improvement of agricultural systems. To enhance the competitiveness of California agriculture, government, university scientists and industry must work together to ensure the application of genetic engineering tools to improve crops.

Determining sulfur-containing amino acids by capillary electrophoresis: a fast novel method for total homocyst(e)ine human plasma.

A high-performance capillary electrophoresis (HPCE) method based on laser-induced fluorescence detection is presented here. It enables the determination of sulfur-containing amino acids within 15 min. Fluorescence of sulfur-containing amino acids in plasma is linear over a range of 50-150 micromol/L for L-methionine, 5-100 micromol/L for L-homocysteine, and 50-200 micromol/L for L-cysteine. For homocysteine, we were able to detect 1 fmol injected, equivalent to a plasma concentration of 10 nmol/L. A similar sensitivity is present for cysteine, an even lower one being found for methionine. The intra- and interassay relative standard deviations are < 1%. High-performance liquid chromatography (HPLC) methods are commonly employed for quantifying blood concentrations of sulfur-containing amino acids. A comparative analysis of HPCE and HPLC quantitation of homocysteine has been carried out in 61 blood samples. Plasma concentrations measured by HPCE were in good agreement with those obtained employing an HPLC-based method, a satisfactory correlation being observed between the concentrations obtained by the two methods (r= 0.9972). Thus, the HPCE-based procedure presented here for the measurement of sulfur-containing amino acids in plasma is a simple, fast, accurate, and very sensitive method, suitable for routine determinations in clinical studies.

Determining sulfur-containing amino acids by capillary electrophoresis: A fast novel method for total homocyst(e)ine human plasma

A high-performance capillary electrophoresis (HPCE) method based on laser-induced fluorescence detection is presented here. It enables the determination of sulfur-containing amino acids within 15 min. Fluorescence of sulfur-containing amino acids in plasma is linear over a range of 50—150 μmol/L for L-methionine, 5—100 μmol/L for L-homocysteine, and 50—200 μmol/L for L-cysteine. For homocysteine, we were able to detect 1 fmol injected, equivalent to a plasma concentration of 10 nmol/L. A similar sensitivity is present for cysteine, an even lower one being found for methionine. The intra- and interassay relative standard deviations are < 1%. High-performance liquid chromatography (HPLC) methods are commonly employed for quantifying blood concentrations of sulfur-containing amino acids. A comparative analysis of HPCE and HPLC quantitation of homocysteine has been carried out in 61 blood samples. Plasma concentrations measured by HPCE were in good agreement with those obtained employing an HPLC-based method, a satisfactory correlation being observed between the concentrations obtained by the two methods (r = 0.9972). Thus, the HPCE-based procedure presented here for the measurement of sulfur-containing amino acids in plasma is a simple, fast, accurate, and very sensitive method, suitable for routine determinations in clinical studies.

Plant breeding: a long-term strategy for the control of zinc deficiency in vulnerable populations

Because trace minerals are important not only for human nutrition but for plant nutrition as well, plant breeding holds great promise for making a significant, sustainable, low-cost contribution to the reduction of micronutrient deficiencies in humans. It may also have important spinoff effects for increasing farm pro-ductivity in developing countries in an environmentally beneficial way. This article describes ongoing plant breeding research that could increase the intake of bioavailable zinc from food staple crops in vulnerable populations in developing countries. The 3 most promising plant breeding strategies toward this goal are as follows: 1) increasing the concentration of zinc, 2) reducing the amount of phytic acid (a strong inhibitor of zinc absorption), and 3) raising the concentrations of sulfur-containing amino acids (thought to promote zinc absorption) in the plant. The agronomic advantages and disadvantages as well as the potential benefits and limitations of each approach for human nutrition are described. Research is currently underway to identify the optimal combination of these approaches that will maximize the effect on human zinc nutrition. Am J Clin Nutr 1998;68(suppl):488S–94S.

Content of sulfur amino acids and vitamin B6 and related enzyme activities in rats with chronic renal failure fed a high methionine diet.

The effect of concentrations of sulfur-containing amino acids, activities of cystathionine gamma-lyase and cystathionine beta-synthase, and level of vitamin B6 were examined following menthionine administration in normal rats and chronically uremic rats with 7/8 nephrectomy. In the uremic rats, the serum levels of methionine, cystathionine, cysteine and taurine increased in proportion to the amounts of methionine administered. The increase of taurine content in the serum and liver was particularly marked. Cystathionine beta-synthase activity in the liver increased with the administration, but the serum level of pyridoxal phosphate decreased markedly. The body weight gain of rats decreased with the administration, and the contents of urea and creatinine in serum increased. Thus, vitamin B6 deficiency in chronically uremic rats administered with large amounts of methionine may reduce growth, lower renal function and cause abnormal metabolism of sulfur-containing amino acids.

Biochemical studies of some non conventional sources of protein. Part 4. The proteins of mango waste stone kernels.

The gross chemical composition, protein content and amino acid composition of mango stone kernels of four Egyptian varieties (Ewsi, Hendi, Fonso and Timour) were investigated. Carbohydrates are the main components of the seed. The protein content varies between 5.0 and 7.2% and the ether extract ranged from 10.8% to 13.6%. High glutamic acid, aspartic acid and leucine content and low concentration of sulfur-containing amino acids are characteristic for the proteins of mango kernels. Lysine level is also low, the concentration of other essential amino acids is acceptable. Sulfur-containing amino acids are the first limiting ones followed by lysine and threonine.

Role of methionine in the regulation of the synthesis of serine hydroxymethyltransferase in Escherichia coli.

The synthesis of serine hydroxymethyltransferase during methionine limitation is different in met A and met B auxotrophs, mutants defective in homocysteine biosynthesis, as compared to met E and met F auxotrophs, mutants which are unable to methylate homocysteine and thus unable to either synthesize methionine de novo or to regenerate it after use via methylation reactions. Methods for the measurement of intracellular concentrations of sulfur-containing amino acids and nucleosides were developed and applied to cultures of the methionine auxotrophs. No definitive correlation between the absolute intracellular concentration of any single metabolite and the rate of serine hydroxymethyltransferase synthesis was found. However, a high correlation (0.92) was found with the ratio of homocysteine to S-adenosylmethionine, with the rate of enzyme synthesis being a hyperbolic function of the ratio. This is consistent with homocysteine acting as an inducer and S-adenosylmethionine as a corepressor of serine hydroxymethyltransferase synthesis with high affinity for a repressor molecule. This correlation holds only during methionine limitation, and was not observed during glucose limitation or in unrestricted cultures with added adenosine.

Concentrations of sulfur-containing free amino acids in lumbar cerebrospinal fluid from patients with consciousness disturbances.

The concentrations of sulfur-containing amino acids (taurine, methionine, cystine, cystathionine, homocystine) in lumbar CSF from patients with consciousness disturbances and controls were measured, and it was investigated whether there was any correlation between the sequential changes of these amino acid concentrations and of the level of consciousness. In all patients, thyrotropin-releasing hormone (TRH) was administered and the changes of levels of consciousness and amino acid concentrations were followed before and after administration. The concentrations of taurine and cystathionine from the patients were significantly lower, and methionine and cystine significantly higher than those from the controls; they returned to the control values in parallel with improvement of consciousness level. Homocystine was not detected in either patients or controls. These results suggest that the alteration in the level of consciousness is associated with distortion of sulfur-containing amino acid metabolism within the central nervous system, at least in the CSF.

The excretion of sulfur compounds in the urine of newborn infants

The excretion of sulfur-containing compounds was determined on the third and sixth day of life in male infants and the results were compared with those previously obtained on fed and fasting men. The output of total sulfur and inorganic sulfate was very low on the third day of life but had increased by the sixth day to levels found in the fasting men, whereas the excretion of mercaptolactate in the newborns decreased from the third to the sixth day of life. These results may be explained by the initial fasting state of neonates followed by an anabolic phase. Neonates excreted acid-labile ester sulfate and mercaptoacetate at levels similar to those found in adults, but the neonatal urine also contained sulfate esters (probably steroid sulfates) that required more drastic acid conditions for hydrolysis. Raised concentrations of sulfurcontaining amino acids (methionine, cystathionine, cyst(e)ine and taurine) were found in neonatal urine in confirmation of earlier reports. The excretion of thiosulfate could only be determined in newborns on the sixth day and was low in comparison with that of adults. High urinary thiocyanate concentrations were found in newborns fed by tobacco-smoking mothers, whereas the excretion of thiocayanate was low in other newborns. The possible medical hazards from the exposure of neonates to thiocyanate are emphasized.

Blood and Liver Concentrations of Glutathione, and Plasma Concentrations of Sulfur-Containing Amino Acids in Chicks Fed Deficient, Adequate, or Excess Levels of Dietary Cysteine

Experiments were conducted with young male chicks to examine the influence of cysteine status on blood and liver glutathione (GSH) concentrations and plasma sulfur amino acids. The equivalence of cystine, cysteine, and GSH as sources of dietary cysteine for the chick was reconfirmed. Whole-blood GSH was unresponsive to dietary cysteine level, but liver GSH increased as dietary cysteine increased from a deficient level to the required level. Excess levels of cysteine (two or four times the chick's requirement) elicited no further increase in hepatic GSH. Plasma cystine concentration increased markedly (i.e., ninefold) and in a linear fashion while plasma cysteine increased only modestly (i.e., twofold) as dietary cysteine level increased.