Sulfur Amino Acid Concentration Research Articles

Total, free, and protein-bound sulphur amino acids in uraemic patients.

Fasting plasma concentrations of sulphur amino acids (sAA) were measured in nine non-dialysed (ND) chronic uraemic patients on conservative treatment, 10 patients on continuous ambulatory peritoneal dialysis (CAPD), nine patients on haemodialysis (HD) treatment, and 10 healthy subjects (HS). Methionine and taurine concentrations were significantly decreased in the CAPD and HD patients and tended to be low in the ND patients. Cysteine sulphinic acid (CSA) levels were significantly higher in all patient groups. Total (t), free (f), and protein-bound (pb) homocysteine (Hcy) and cysteine (Cys) were significantly increased in all patient groups. Serine, a substrate for cystathionine synthesis from Hcy, showed significantly lower concentrations in all patient groups. The percentages of pbHcy were significantly higher in the CAPD and HD patients than in the ND patients (P < 0.0001, P = 0.002 respectively) or in the HS (P < 0.0001, P = 0.008 respectively), whereas the percentages of pbCys in CAPD and HD patients were significantly higher than in ND patients (P = 0.0006, P = 0.009 respectively) and tended to be high without reaching statistical significance compared to the HS. A single HD treatment decreased tHcy by 26%, fHcy by 39%, and pbHcy by 22%, as well as tCys by 40%, fCys by 54%, and pbCys by 27%. The tHcy concentration, although decreased by HD treatment, remained higher than in HS, whereas tCys was normalized by the dialysis session. In addition, HD treatment significantly decreased the plasma concentrations of methionine, CSA, taurine, and serine. We conclude that, except for methionine and taurine, the plasma sAA in their different forms are markedly increased in dialysed and non-dialysed uraemic patients. The percentages of pbHcy and pbCys were significantly higher in dialysed than in ND uraemic patients. HD treatment can normalize the tCys concentration, and decrease the tHcy concentration but not normalize it. The observed hyperhomocysteineaemia and low taurine levels may contribute to the high incidence of cardiovascular disease in uraemic patients.

Use of Amino Acid Profiles of Pretermand Term Human Milks in Evaluating Scoring Patterns for Routine Protein Quality Assessment of Infant Formulas

Reports on the amino acid composition of human milk vary considerably with respect to concentrations of sulfur amino acids. Often, analyses forego tryptophan determination. A complete analysis of protein and amino acid concentrations was performed on human milk samples (5-10 days postpartum) collected from mothers of preterm (gestations of 25-32 weeks) and term (gestations of > 36 weeks) infants. Careful attention was given to quantitate amino acids such as cysteine and tryptophan, which are vulnerable to acidic hydrolysis conditions. Differences in concentrations of total amino acids (expressed on protein basis) between preterm and term milks were small, despite the higher true protein content of preterm milk versus term milk (19.20 versus 12.60 g/L). The methionine + cyst(e)ine contents of term and preterm milks (3.72-3.84 g/100 g protein) were comparable with those reported in 1991 by the Food and Agricultural Organization/World Health Organization (FAO/WHO) for mature human milk (4.20 g/100 g protein) but higher than those reported in 1991 by the European Commission (2.9 g/100 g protein). The amino acid pattern of human milk obtained in this study confirms that the 1991 FAO/WHO amino acid scoring pattern for predicting protein quality of infant formulas is representative of the amino acid quality of both preterm and term human milks.

Sulfur amino acid metabolism in infants on parenteral nutrition

In the infant on parenteral nutrition, cysteine supplementation has been suggesteddue to low levels of hepatic cystathionase activity limiting synthesis from methionine. We have examined the plasma concentrations of sulfur amino acids in four groups of post-surgical infants requiring parenteral nutrition receiving (A) a low methionine + cysteine + taurine formula, (B) a high methionine formula (non-steady state), (C) a high methionine formula (steady state), and (D) a high methionine + cysteine formula. Plasma methionine concentrations were above the normal reference range (2.2–4.9 micromole/dL) of normal breast-fed infants in Groups B (15.9 ± 10.7 micromole/dL) and D (5.7 ± 1.9 micromole/dL) and at the upper limit for Group C (4.9 ± 1.7 micromole/dL). Total cysteine/cystine concentrations (normal reference range, 10.2–20.4 micromole/dL) were highest in Groups A (18.9 ± 3.5 micromole/dL) and D (16.8 ± 5.3 micromole/dL) that received cysteine HCI supplementation, and lowest in Group B (8.6 ± 3.7 micromole/dL) that received no cysteine in non-steady state. All plasma free cystine concentrations were below the normal reference range (3.6–6.8 micromole/dL). Plasma taurine concentrations were not significantly different among the four groups and all were within the normal reference range (0.6–16.2 micromole/dL). The strikingly elevated methionine and low total cysteine/cystine values in Group B suggested the existence of a feedback loop of methionine conversion below the level of homocysteine. Equilibrium of methionine and cysteine/cystine plasma concentrations did occur, in time. Parenteral cysteine administration resulted in a greater proportion of plasma free cysteine concentration, but not cystine. The proportion of free to bound cysteine/cystine, as well as the proportion of free cystine to cysteine, was not normal during parenteral nutrition with or without cysteine HCI supplementation. Little benefit in plasma concentrations was derived from cysteine HCI supplementation to a high methionine formulation.

Sulfate Incorporation into Organic Bone Matrix of the Tibiotarsus of Broiler Chicks is Reduced by Excess Dietary Methionine

Two experiments were conducted in broiler chicks to determine whether dietary imbalances of sulfur amino acids (SAA), vitamin A, or interactions between the two nutrients could influence organic bone matrix metabolism measured with L-[35 S]-methionine. In the first experiment, in vivo incorporation of 35 S into the tibiotarsal bone matrix of 2-wk-old birds was unaffected by vitamin A treatment of 10 and 100 times the requirement when compared with that of birds receiving recommended amounts of vitamin A. However, 35 S incorporation was significantly reduced by increasing the SAA concentration of the diet to 1.5 times the requirement relative to lysine. In the second experiment, in vitro incorporation of 35 S, derived from L-[35 S]-methionine, into bone matrix was reduced in birds consuming a diet containing 1.5 times the methionine requirement relative to lysine (Diet HS) when compared with those receiving .75 (Diet LS), 1.0 (Diet NS), or 1.25 (Diet MS) times the requirement. Birds consuming Diet LS incorporated significantly more 35 S into organic bone matrix than birds consuming the other three diets. Although the ratio of SAA to lysine was that recommended (.76:1), on a weight basis the concentration of SAA in diet NS was relatively high (11.48 g/kg diet) compared with the NRC (1984) recommendation of 9.3 g/kg diet. The results show that excess SAA can affect organic bone matrix metabolism and suggest that SAA may play a role in the etiology of tibial dyschondroplasia. They also indicate the importance of distinguishing between nutrient content of the diet expressed as a ratio and that expressed on a weight basis.

Thiazolidine-4-Carboxylate and 2-Phenylthiazolidine-4-Carboxylate are Active as Cysteine Precursors but have no Effect on Growth of a Methionine-Dependent Tumor in Rats

Diets with partial replacement of sulfur amino acids by thiazolidine-4-carboxylate or 2-phenylthiazolidine-4-carboxylate were fed to normal and to rhabdomyosarcoma-bearing rats (methionine-dependent tumor) to evaluate their efficacy as cysteine precursors and as antitumor agents. Food intake, weight gain, food efficiency and plasma albumin and plasma sulfur amino acid concentrations were not different when these diets were compared with isosulfurous diets containing either methionine or N-acetylcysteine. 2-Phenylthiazolidine-4-carboxylate induced a lower plasma glutathione (GSH) level than the latter diets. Tumor-bearing rats had lower plasma GSH concentration. A negative linear relationship was found between plasma GSH levels and tumor weight and also the tumor weight: body weight ratio. This could mean that the tumor becomes the most important organ in the uptake of GSH. However, there was also a significant positive correlation between plasma GSH and albumin, suggesting a reduced GSH hepatic synthesis due to amino acid uptake by the tumor. There were no differences in tumor growth among rats receiving diets containing N-acetylcysteine, thiazolidine-4-carboxylate or 2-phenylthiazolidine-4-carboxylate.

Electrogenic uptake of sulphur‐containing analogues of glutamate and aspartate by Müller cells from the salamander retina.

1. The effect of sulphur-containing analogues of glutamate and aspartate on the membrane current of glial cells was studied by whole-cell clamping Müller cells isolated from the salamander retina. 2. L-Cysteic acid (CA), L-cysteinesulphinic acid (CSA), L-homocysteic acid (HCA), L-homocysteinesulphinic acid (HCSA) and S-sulpho-L-cysteine (SC) all evoked an inward membrane current that was large at negative potentials, and was smaller (but did not reverse) at more positive potentials up to +30 mV. 3. Removal of external sodium ions abolished the amino acid-evoked currents. Whole-cell clamping with pipettes containing no potassium led to a rapid suppression of the currents, that did not occur when potassium was included in the pipette. 4. The dependence of the currents on sulphur-containing amino acid concentration obeyed first-order Michaelis-Menten kinetics. The current evoked by co-application of L-glutamate and a sulphur-containing analogue was smaller than the sum of the currents produced by glutamate alone and by the sulphur analogue alone. 5. These data are consistent with the sulphur amino acid-evoked current being caused by uptake on the electrogenic glutamate uptake carrier, which co-transports an excess of Na+ ions into the cell, and counter-transports one K+ ion out of the cell. 6. The apparent Km (Michaelis-Menten constant) values for activation of uptake by CA (6 microM) and by CSA (60 microM) are low enough for uptake on the glutamate uptake carrier to be a plausible mechanism for terminating the postulated neurotransmitter action of these agents. However, the apparent Km values for uptake of HCA (2.95 mM), HCSA (1.65 mM) and SC (greater than 1 mM) are much higher than the EC50 (half-maximal effective concentration) concentrations for these agents' activation of NMDA (N-methyl-D-aspartate) channels. 7. Comparing the concentrations of sulphur amino acids needed to activate NMDA channels with their rate of uptake suggests that their potency for causing excitotoxic damage should follow the sequence HCA greater than SC greater than HCSA greater than Glu greater than CSA greater than Asp greater than CA.

The Influence of Severe Drought on Selected Nutritional Characteristics of Commercial Corn Hybrids

In 1988, after a severe drought during the growing season, samples from 12 commercial corn varieties were collected from the same test area. The average yield was 85 bu/acre (1 bu = 35.24 L; 1 hectare = 2.47 acres), which was 50% lower than yields of the previous year from the same area. Average CP was 9.50% compared with 8.80% recommended by the National Research Council (NRC) in 1984, but there were minimal differences between NRC recommended and analyzed concentrations of methionine and lysine. Analyzed total sulfur amino acid concentrations were approximately 10% higher than NRC levels. Regression equations based on CP concentrations resulted in significantly higher predicted values for lysine, methionine, and methionine plus cystine. The results suggest that when protein values in corn are elevated due to an environmental stress, conservative amino acid values should be used for dietary formulation.

Research Note: Characterization of Two Samples of Corn that Vary in Bushel Weight

Two samples of corn differing substantially in bushel weight were obtained from a commercial feed mill. The light weight sample (606 g/L; 47 lb/bu) was higher in protein (9.3%) and lower in ether extract (2.95%) than the normal weight corn (696 g/L; 54 lb/bu), which contained 8.1% protein and 3.43% ether extract. The determined TME of the corn samples on a dry matter basis did not differ significantly (3.81 vs. 3.83 kcal/kg). The normal corn had increased levels of lysine, methionine, and methionine plus cystine when the amino acid levels were compared as a percentage of total amino acids. No differences were observed when comparisons were made as a percentage of the total sample. In the light corn sample, the analyzed lysine and sulfur amino acid concentrations (percentage amino acids/percentage CP) were 13 to 16% lower than calculated values derived from published prediction equations. In the normal corn, the differences were only 8 and 3%, respectively.

Dietary Discrimination by Molting White-Crowned Sparrows Given Diets Differing Only in Sulfur Amino Acid Concentration

In certain circumstances, wild animals may obtain adequate nutrition merely by random consumption of foods but, in other circumstances, may need to feed selectively for specific nutrients. For instance, it has been argued that requirements for certain amino acids may be so great during periods of production such as egg laying or molt that highly selective feeding is necessary to avert malnutrition. We evaluated the ability of captive molting white-crowned sparrows to choose between two semisynthetic diets (Choice) that were essentially identical, except in sulfur-amino acid (SAA = cyst(e)ine + methionine) concentration. The high-SAA diet was more than nutritionally adequate, and the low-SAA diet was inadequate for molting sparrows. Two parallel experimental groups were fed only the high-SAA diet (Control) or the low-SAA diet (Deficient), respectively. Food was supplied to each bird in two glass food cups, side by side. Choice birds thus had free access to a high-low-SAA-diet pair, while Control (high-high-diet pair) and Deficient (low-low-diet pair) birds had free access to right- or left-hand cups containing identical diets. Daily food intake by Control birds was 50:50 from rightand left-hand cups before, during, and after molt. Their body-mass variation and molt pattern (duration = ca. 54 days) were normal. Daily food intake by Deficient birds was less (25%-30%); body mass was less (ca. 15%); and molt was longer (105 days) than in Control or Choice birds. Many new feathers in Deficient birds were malformed. A subgroup of the Deficient group that was given a high-low-diet choice midway through the experiment quickly regained normal body mass and accelerated molt above the normal rate, so that molt was completed in 75 days. Daily food intake, body mass, and pattern and duration of molt in the Choice birds were indistinguishable from these variables in Control birds. Choice birds consumed a 50:50 ratio of diets before and after molt but during molt preferentially consumed the high-SAA diet in rough proportion to molt intensity, with a mid-molt plateau at about 65% highSAA diet. Tests involving switching of diet (food-cup) locations showed that the birds can sense diet quality and respond to altered diet location within at least 16 h (1 feeding day).

The effect of fasting on leukocyte and plasma glutathione and sulfur amino acid concentrations

Leukocyte and plasma concentrations of free glutathione, cysteine, methionine, and taurine, and total glutathione and cysteine concentrations were determined in healthy human subjects before and during a seven-day period of total energy deprivation. In leukocytes a progressive decline in total glutathione concentration was found during seven days of starvation due to a decrease in free glutathione content. An increased mixed protein-bound glutathione concentration was calculated, whereas the total cysteine level was unaltered. Fasting resulted in a decreased plasma concentration of free glutathione, whereas the total glutathione level remained unchanged. Free leukocyte concentrations of taurine and methionine were reduced, whereas plasma sulfur amino acid levels were essentially unaffected. These results probably reflect a limited availability of sulfur amino acids during fasting, when glutathione is used as cysteine reservoir for synthesis of other vital sulfur containing compounds. The potential use of leukocyte glutathione, methionine, and taurine concentrations as intracellular indicators of sulfur amino acid deficiency are stressed.

Sulfur Amino Acid Nutrition during Molt in the White-Crowned Sparrow. 1. Does Dietary Sulfur Amino Acid Concentration Affect the Energetics of Molt as Assayed by Metabolized Energy?

To test the hypothesis that the dietary intake of the sulfur-con- taining amino acids (SAA) methionine and cyst(e)ine affects energy intake or the allocation of energy to production and oxidation, respectively, we fed five groups of White-crowned Sparrows (Zonotrichia leucophrys gambelii) five isocaloric, isonitrogenous diets before, during, and after their postnuptial molt. The diets ranged in SAA content from sub- to superadequate in relation to standards es- tablished for poultry, and from very low to very high in relation to the SAA content of natural foods. The patterns of plumage replacement were indistin- guishable among the five groups. The body weights of all birds decreased sharply at the onset of molt, as is typical for this and other species, and then gradually increased through early molt and stabilized during mid- and late molt. The com- ponents of energy balance (gross energy intake, energy utilization coefficient, ca- loric density of excreta, total excretory energy output) did not differ significantly or consistently among the five groups. Likewise, the net energy of molt, as esti- mated by subtracting the maintenance requirement for metabolized energy from the expenditure during molt by the same birds, ranged from 582 to 611 kJ, but without significant differences among the groups and without consistent corre- lations to the diets. The grand average was 605 kJ/25-g bird. Hence, we are unable to verify the predictions of the amino acid model for the determination of the energy requirements of molt.

Protein-Amino Acid Evaluation of Steam-Processed Feather Meal

Five chick bioassays were carried out to evaluate the protein quality of a commercially available, steam-processed feather meal. The meal was assayed and found to contain 86.8% CP, .45% methionine, 4.19% cystine, 1.72% lanthionine, and 1.45% lysine. Fed as the sole source of protein, methionine and lysine were first- and second-limiting amino acids, respectively; histidinc and tryptophan were equally third limiting. Two assays conducted to establish bioavailable cystine concentrations yielded values of 2.92% in one assay and 2.89% in the other. Based upon the total sulfur amino acid concentration as determined chromatographically and, converting methionine and lanthionine to cystine equivalents, a bioavailability of 52% was calculated. With methionine-fortified corn-soybean meal diets it was shown that at least 10% of the dietary crude protein (24%) could be provided as feather meal. With methionine and lysine supplementation, up to 40% of the dietary crude protein could be supplied by feather meal with little depression in chick rate and efficiency of weight gain.

Hypermethioninemia associated with methionine adenosyltransferase deficiency: Clinical, morphologic, and biochemical observations on four patients

Four patients with hypermethioninemia were ascertained in neonatal mass metabolic screening programs. Hypermethioninemia has persisted in all cases. There were no other abnormalities in sulfur-amino acid concentrations, and routine serum chemical determinations, including the results of "liver function" tests, were normal. Hepatic methionine adenosyltransferase activity was found to be low, ranging from 7.8 to 17.5% (mean 11.4%) of the normal adult control value. Electron microscopy of liver showed increased smooth endoplasmic reticulum, decreased rough endoplasmic reticulum, and increased lysosomes; short breaks in the outer membranes of mitochondria were present to a variable extent. Despite the persistent hypermethioninemia, which argues for continued deficiency of hepatic MAT, all four children appear well. This ostensible well being may be a result of the normal activity of extrahepatic MATs, as shown for erythrocytes and for cultured fibroblasts and lymphoid cells.

EFFECT OF DIETARY SULFUR AMINO ACID LEVEL ON COPPER-INDUCED GROWTH DEPRESSION IN RATS

A growth assay was conducted with rats to determine if copper-induced growth depression is related to dietary sulfur amino acid concentration. In the absence of added copper, methionine addition to the basal diet had no effect on either gain or gain/feed. However, the growth depressing effect of 750 mg/kg copper was totally alleviated with the addition of 0.18% methionine.

The sparing action of inorganic sulphate on sulphur amino acids in practical broiler diets: The replacement of some of the supplementary methionine in broiler finisher diets1

1. Three trials, using practical broiler finisher diets, were carried out to determine to what extent synthetic methionine can be replaced by sodium sulphate. 2. In all three trials responses in weight gain and food conversion ratio were obtained to increments of sodium sulphate in diets containing sub‐optimal concentrations of sulphur amino acids. 3. The effectiveness of sodium sulphate during the finishing period was not higher than had been previously found in younger chicks, and in most cases ranged from 20% to 50% that of synthetic methionine. This efficiency increased after 2 weeks on these diets, in two of the trials. 4. The addition of either synthetic methionine or sodium sulphate decreased relative food consumption, which was apparently increased by suboptimal levels of dietary sulphur.