L-amino Acid Mixture Research Articles

Studies on the Metal-Protein Complex. X.

Crystalline Glu, Lys and Cys had the antioxidative activities and inhibited the oxidative activity of ferrous chloride by the Active Oxygen Method (98°C).The inhibitory activities of the mixtures of L-amino acids containing Glu, Lys or Cys on the oxidative activity of ferrous chloride were proportional to those of L-amino acids described above. The inhibitory activities of peptides on the oxidative activity of metal salt were not proportional to those of the mixtures of the constituent L-amino acids.Polypeptides and proteins had small inhibitory activities on the oxidative activity of iron (II) chloride in comparison with Glu or Lys. Peptides and the mixtures of the constituent L-amino acids inhibited the oxidative activity of copper (II) sulfate.Iron and copper seem to adhere loosely on the surface of crystalline peptides under the conditions of Active Oxygen Method on the basis of IR spectra of the obtained metal-peptide complexes.However, the loss of the oxidative activities of metal salts was nots proportional to the amounts of metal in the metal-peptides or metal-L-amino acids complexes.

Plasma and urinary amino acids and selected sulfur metabolites in young men fed a diet devoid of methionine and cystine

A preliminary investigation was conducted to explore the use of plasma methionine and cystine for determining human sulfur amino acid requirements. Measurements of urinary methionine, cystine, taurine, and inorganic sulfate were included. After a 3-day control period, three young men were fed for 8 days a diet containing a purified -l-amino acid mixture, patterned after egg protein but devoid of methionine and cystine. Fasting plasma methionine and cystine levels showed little decrease during the 8-day period. Urinary cystine and taurine responses were inconsistent among the subjects. Urinary methionine and inorganic sulfate levels decreased markedly within a few days after feeding of the experimental diet, and may be useful criteria for determining human sulfur amino acid requirements.

Canine gut receptors mediating pancreatic responses to luminal L-amino acids

Pancreatic protein and bicarbonate outputs were measured in dogs with pancreatic fistulas receiving intravenous secretin while individual L-amino acids or mixtures of L-amino acids were perfused into proximal intestine, Both phenylalanine and tryptophan were potent stimuli of pancreatic secretion; alanine, leucine, and valine increased protein outputs but their effects were small and not statistically significant. Six other amino acids were ineffective. Tryptophan perfused together with phenylalanine augmented responses to phenylalanine; methionine, ineffective when perfused alone, did not alter responses to phenylalanine when perfused with the latter. Responses to phenylalanine perfused at concentrations above 8 mM were dependent on load and were mediated by lengths of proximal bowel greater than 10 cm.

Amino acids as repressors of nitrogenase biosynthesis in Klebsiella pneumoniae

Nitrogenase biosynthesis in Klebsiella pneumoniae including mutant strains, which produce nitrogenase in the presence of NH 4 + (Shanmugam, K.T., Chan, Irene, and Morandi, C. (1975) Biochim. Biophys. Acta 408, 101–111) is repressed by a mixture of L-amino acids. Biochemical analysis shows that glutamine synthetase activity in strains SK-24, SK-28, and SK-29 is also repressed by amino acids, with no detectable effect on glutamate dehydrogenase. Among the various amino acids, L-glutamine in combination with L-aspartate was found to repress nitrogenase biosynthesis completely. In the presence of high concentrations of glutamine (1 mg/ml) even NH 4 + repressed nitrogenase biosynthesis in the strains SK-27, SK-37, SK-55 and SK-56. Under these conditions, increased glutamate dehydrogenase activity was also detected. Physiological studies show that nitrogenase derepressed strains are unable to utilize NH 4 + as sole source of nitrogen for biosynthesis of glutamate, whereas back mutations leading to NH 4 + utilization results in sensitivity to repression by NH 4 +. These findings suggest that amino acids play an important role as regulators of nitrogen fixation.

Effect on fecal output of various dietary nitrogen sources in pig-tailed monkeys (Macaca nemestrina) fed fiber-free, semisynthetic diets

Fiber-free liquid diets containing isonitrogenous amounts of various dietary nitrogen sources were fed to five adult male pig-tailed monkeys (Macaca nemestrina) with a mean weight of approximately 10 kg. All liquid diets supplied 3.0 g N/DAY PER MONKEY AND MAINTAINED THE ANIMALS IN A POSTIVE NITROGEN BALANCE. Initial baseline fecal output data were obtained by feeding the animals a commercial solid monkey chow. The dietary nitrogen sources fed were a) egg white protein, b) an enzymatic hydrolysate of fish protein supplemented with L-amino acids to simulate the egg albumin pattern, c) a mixture of pure L-amino acids simulating the egg pattern, d) a casein hydrolysate supplemented with amino acids, and e) an amino acid mixture with Rose's pattern. Total fecal matter, dry fecal matter, percent of moisture, fecal nitrogen, lipids and ash were determined for a 10-day period for each experimental diet. A very significant difference (P smaller than 0.001) was noted between each liquid diet and the solid chow, but no significant differences were found between the various fiber-free liquid diets, pointing to the effect of fiber as a major factor affecting fecal output. Monkeys fed liquid diets excreted fecal matter with a mean of 12.9 g/day, of which 4.7 g/day was dry feces (fecal dry matter 28.5%). Fecal nitrogen was found to be 0.25 g, fecal lipids were 0.19 g, and fecal ash was 0.59 g/day per monkey, respectively.

Parenteral nutrition in seriously III neonates: Search for the ideal mixture

Five patients who had parenteral nutrition with a casein hydrolysate and dextrose mixture were compared with five patients who received a synthetic L-amino acid and dextrose mixture. The incidence of metabolic complications and sepsis was lower in the infants who had the synthetic Lamino acid and dextrose mixture. A protein intake of 2 gm/kg/day was better tolerated than was one of 4 gm/kg/day. It is concluded that at present the best amino acid and dextrose mixture is made up of synthetic L-amino acids and dextrose and is adjusted to a protein load of 2 gm/kg/day.

Plasma Threonine Response Curve and Threonine Requirements of Young Men and Elderly Women

Studies were conducted in eight male M.I.T. students and 13 subjects 72 ± 5 years of age on the relationship between plasma threonine concentration, threonine intake and threonine requirement. The formula diet contained an L-amino acid mixture, patterned as in egg protein, and provided N equivalent to 0.5 g protein (N × 6.25) per kilogram body weight per day with graded reductions in threonine intake from 18 to 1 mg/kg/day. Fasting and 3.5-hour postprandial plasma threonine levels were measured at the end of each consecutive dietary period, usually lasting 5 days. The fasting plasma threonine data were evaluated statistically to identify the point at which plasma threonine remained constant despite further reductions in intake. This “lower breakpoint” on the plasma threonine response curve was assumed to occur at the intake of the amino acid which just meets the minimum physiological requirement. It was estimated to be 7 ± 2 mg/kg/day for eight young males and for 11 elderly women it was essentially identical, being 8 ± 2 mg/kg/day. Alternative nutritional interpretations of the “lower breakpoint” on the plasma amino acid response curve in adult human subjects are discussed.

Nutritional Features of Bacteroides fragilis subsp. fragilis

Studies of three reference strains of Bacteroides fragilis subsp. fragilis showed that they grow well in a minimal defined medium containing glucose, hemin, vitamin B(12), minerals, bicarbonate-carbon dioxide buffer, NH(4)Cl, and sulfide. The vitamin B(12) requirement of 0.1 ng/ml was replaced with 7.5 mug of methionine. Cysteine or sulfide was an excellent source of sulfur, thioglycolate was a poor source, and thiosulfate, methionine, beta-mercaptoethanol, dithiothreitol, sulfate, or sulfite did not serve as sole sources of sulfur. Neither single amino acids, nitrate, urea, nor a complex mixture of L-amino acids or peptides effectively replaced ammonia as the nitrogen source. Comparative studies with a few strains of other subspecies of B. fragilis including B. fragilis subsp. vulgatus, B. fragilis subsp. thetaiotaomicron, and B. fragilis subsp. distasonis indicate that they exhibit similar growth responses in the minimal medium. A single strain of B. fragilis subsp. ovatus required other materials. The results indicate the great biosynthetic ability of these organisms and suggest that, in their ecological niche within the large intestine, many nutrients such as amino acids are in very low supply, whereas materials such as ammonia, heme, and vitamin B(12), or related compounds, must be available during much of the time.

Serum amino acids in young men consuming diets differing in level and pattern of amino acids

Six healthy male volunteers, aged 21 to 31 years, participated in an 81-day study of the effect of dietary nitrogen level and the pattern of dietary amino acids on serum amino acids. Ten different formula diets were consumed, nitrogen being supplied from mixtures of synthetic l-amino acids. Results indicated that although serum amino acids are altered within 3 days after a change in diet, they do not reflect the particular amino acid pattern consumed. Variations in levels of serum amino acids were evident when the total amount of dietary nitrogen was shifted. When dietary nitrogen was lower, there were increases in nonessential amino acids, especially alanine, and decreases in essential amino acids, mainly those with branched chains.

Metabolic acidosis resulting from intravenous alimentation mixtures containing synthetic amino acids

Abstract Hyperchloremic metabolic acidosis was observed in 11 infants receiving total parenteral nutrition containing mixtures of synthetic L-amino acids. The observed acidosis was not due to excessive gastrointestinal or renal losses of base as judged by the stool undetermined anion content and the urinary net acid excretion, nor was it due to infusion of preformed hydrogen ion as judged by the titratable acidity of the synthetic amino acid mixtures. Instead, the synthetic amino acid mixtures contain an excess of cationic amino acids in relation to anionic amino acids or other organic anions. Metabolism of these cationic amino acids results in a net excess of hydrogen ion, explaining the observed acidosis.

Metabolic acidosis resulting from intravenous alimentation mixtures containing synthetic amino acids.

Abstract Hyperchloremic metabolic acidosis was observed in 11 infants receiving total parenteral nutrition containing mixtures of synthetic L-amino acids. The observed acidosis was not due to excessive gastrointestinal or renal losses of base as judged by the stool undetermined anion content and the urinary net acid excretion, nor was it due to infusion of preformed hydrogen ion as judged by the titratable acidity of the synthetic amino acid mixtures. Instead, the synthetic amino acid mixtures contain an excess of cationic amino acids in relation to anionic amino acids or other organic anions. Metabolism of these cationic amino acids results in a net excess of hydrogen ion, explaining the observed acidosis.

Plasma Amino Acid Response Curve and Amino Acid Requirements in Young Men: Valine and Lysine

A total of 14 young men were studied to determine the relationships between the concentration of free valine or lysine in blood plasma, and the dietary intake and daily requirement for each of these amino acids. The diet, containing an L-amino acid mixture, which was patterned as in egg protein, supplied nitrogen equivalent to about 0.5 g egg protein (N × 6.25)/kilogram body weight/day. In three separate experiments with a total of 10 subjects, dietary valine intake varied between 4 and 20 mg/kilogram body weight, and in another with four subjects, lysine intake ranged from 1 to 24 mg/kilogram body weight. The free valine level in fasting plasma was relatively constant at valine intakes below 14 to 16 mg/kilogram body weight/day and increased above this intake level. Crude nitrogen balances in these subjects approached equilibrium or were positive at valine intakes of about 12 to 14 mg/kg. Considering integumental and sweat nitrogen losses, it appears that fasting plasma valine levels begin to rise at an intake of 14 to 16 mg/kg, which is presumably the minimum requirement for these subjects. This technique should be useful to determine valine requirements under various conditions. In the lysine study three subjects remained in nitrogen balance throughout. Mean fasting plasma lysine levels were relatively constant at and below an intake of 6 mg/kilogram body weight and were 13 and 18% higher at the 7 and 24 mg/kg lysine intakes, respectively. In comparison with the valine findings, fasting plasma lysine levels would not appear as useful a response criterion to assess the human maintenance requirement for this amino acid.

Plasma Amino Acid Response in Young Men Given Diets Devoid of Single Essential Amino Acids

Studies were conducted on the response of plasma amino acid levels in young, male MIT students to diets lacking in phenylalanine-tyrosine, threonine, lysine, valine, leucine or isoleucine. A purified L-amino acid mixture was the sole source of dietary “protein” and supplied a nitrogen level equivalent to about 0.5 g egg protein (N × 6.25) per kilogram body weight. The subjects were studied during a 3-day control period while consuming their usual diet and during a 12-day period of receiving the experimental diet. Blood samples were taken at 8 am after an 11-hour overnight fast and 3 hours after breakfast during the control period and again after 4, 8 and 12 days during the amino acid diet period. The initial fasting plasma levels of phenylalanine, lysine, isoleucine and leucine were reduced by less than 30% during the 12-day period of consuming diets deficient in the respective amino acid, whereas the levels of threonine and valine were reduced by approximately 50% within 4 days after initiation of the respective amino acid-free diet. The leucine-free diet resulted in a significant increase in the levels of valine and isoleucine in fasting and postprandial plasma whereas the valine- and isoleucine-free diets did not affect the fasting levels of the other branched-chain amino acids. These results are discussed in relation to the plasma amino acid approach for estimating human amino acid requirements.

Hyperammonemia resulting from intravenous alimentation using a mixture of synthetic L-amino acids: A preliminary report

Hyperammonemia has been observed in three infants receiving total parenteral alimentation in which the nitrogen source was a mixture of synthetic L -amino acids (FreAmine). Two of the three infants developed lethargy, unresponsiveness, and twitching movements of the eyes and extremities followed by grand mal seizures. The hyperammonemia and associated clinical signs could be corrected by administration of 2 mmoles per kilogram of arginine-glutamate or 3 mmoles per kilogram of arginine-HCl and could be prevented by addition of as little as 0.5 to 1.0 mmoles per kilogram of arginine-HCl to the daily infusate. These observations make it mandatory to monitor blood ammonia levels in any infant receiving total parenteral alimentation.

Long-Term Complete Intravenous Nutrition in Man

The results of an investigation of complete intravenous (i.v.) nutrition for 7 months and 13 days in a 43-year-old woman prove that a good nutritional state can be maintained for a long time, in cases where oral feeding is impossible, by i.v. administration of fat emulsions supplemented with a complete L-amino acid mixture, carbohydrates, electrolytes, vitamins, trace elements and water. During the period of treatment her nutritional condition improved and she gained 10 kg in weight without fluid retention. A mild anemia developed, however. Some interesting findings of this study were: (1) in preventing thrombophlebitis the intermittent i.v. administration was found superior to the continuous method; (2) the weight gain was considered to be caused by fat deposition in the existing cells; (3) a positive nitrogen balance was obtained at 4.0 g N and 1,830 kcal/day; (4) the composition of the adipose tissue was reversibly influenced by the fat emulsion, Intralipid; (5) the plasma cholesterol values increased in spite of the administration of about 50 g of linoleic acid/day; (6) the effects on the liver were mild as judged by liver biopsies and liver function tests, and (7) a tendency to megaloblastic anemia was caused by treatment with phenytoin and could be counteracted by an increased i.v. administration of folate.

In vitro amino acid incorporation by the post-mitochondrial supernatant from rat liver

Interest in the use of the post-mitochondrial supernatant (PM-supernatant) for the study of in vitro amino acid incorporation arose from experiments indicating that the ribosomal aggregation of the PM-supernatant system more nearly represented that of the intact cell than did other ribosomal preparations. The PM-supernatant system was found to be 25 or 50 % more active than the microsomal and ribosomal amino acid incorporation systems. For PM-supernatant in vitro incorporation of l-[ 14C]valine into acid insoluble material, ATP, GTP, an energy generating system, Mg 2+, K +, and a mixture of l-amino acids were necessary. Sephadex G-25 column chromatography of the PM-supernatant, pH 7.4, and presence of glutathione during homogenization of the tissue were necessary for optimal PM-supernatant in vitro incorporation. Under these conditions the rate of l-valine incorporation by the PM-supernatant from 0.17 to 0.20 nmoles/min per mg RNA for a liver from a fed rat. Fasting (20 h) prior to sacrifice, resulted in a 30–40 % decrease in amino acid incorporation by the PM-supernatant as well as a decrease in ribosomal aggregation. The decrease in PM-supernatant incorporation by fasting was found to be associated with both polysomal and cell sap factors.

The effect of the administration of L-tryptophan on synthesis of urea and gluconeogenesis in man.

Inhibition of phosphoenolpyruvate carboxykinase (EC 4.1.1.32) after L-. tryptohan administration has previously been indicated in animal experiments. To see if a similar phenomenon would be detected in man and if such an inhibition would result in decreased glucose and urea production by the liver, experiments were performed with 3 healthy subjects. Tryptophan was given by stomach tube located in the duodenum to 3 volunteers kept on a carbohydrate-free diet for 3 days. On the 4th day a mixture of L-amino acids was infused continuously for 3 hours. Glucose and urea production from the liver were found to be decreased following tryptophan administration. Concurrent measurements of pyruvate, lactate, α-ketoglutarate, acetoacetate, s-hydroxybutyrate, aspartate and glutamate in arterial and liver vein blood indicated that phosphoenolpyruvate carboxykinase was inhibited. This inhibition was judged to be the direct cause of the reduction in glucose production and indirectly the cause for the fall in urea production.

Plasma Tryptophan Response Curve and Its Relation to Tryptophan Requirements in Young Adult Men

A total of 17 adult human subjects was studied to determine the relationships between the concentration of free tryptophan in fasting and postprandial blood plasma, dietary tryptophan intake, and the daily requirement for this amino acid. The diet, containing an L-amino acid mixture, which was patterned as in egg protein, furnished nitrogen equivalent to 0.5 g egg protein per kilogram body weight/day. In two separate experiments dietary tryptophan intake was varied over a range of 1.0 to 8.7 mg/kilogram body weight. Plasma tryptophan concentration was constant above and below tryptophan intakes of 5 and 3 mg/kilogram body weight, respectively, and changed linearly with altered tryptophan intake within this range. The level of dietary tryptophan above which a linear increase in plasma tryptophan occurred was taken to be the requirement level. Nitrogen balance measurements indicated a tryptophan requirement of 2 to 2.6 mg/kilogram body weight whereas the plasma tryptophan data suggested a requirement of about 3 mg/kilogram body weight. The present nitrogen balance data, which did not include integumental and sweat nitrogen losses, probably underestimated tryptophan needs.

The absorption of amino acids from the rumen of the sheep. I. The loss of amino acids from solutions placed in the washed rumen in vivo

L-histidine, glycine, and L-amino acid mixtures were placed in the washed rumen of sheep in concentrations similar to those found under normal feeding conditions. The amounts of individual amino acids lost from the rumen over a 4 hr period ranged from virtually zero to 50% of the initial concentration of amino acids placed in the rumen. It was calculated that this could account for 6% of the total nitrogen absorption from the rumen. The amount of L-amino acids lost from the rumen depended on their initial concentration and on the concentration of other amino acids present. The branched chain amino acids showed the most rapid absorption.

Pathogenesis of maple-syrup-urine disease: observations during dietary management and treatment of coma by peritoneal dialysis

Experiences with the management of a case of maple-syrup-urine disease from early infancy to death at 18 months of age are summarized. The use of a mixture of l-amino acids as the basis of a diet restricted in the branched-chain amino acids allowed the inclusion of a maximal amount of natural protein as the source of the essential branched-chain amino acids. The apparent importance of this natural source of the branched-chain amino acids for normal growth is emphasized. Myelination of the brain was normal on histological examination. The use of peritoneal dialysis for the treatment of coma which had not responded to vigorous intravenous therapy is discussed. Clear-cut neurological improvement occurred during dialysis without concomitant improvement in the metabolic acidosis. The branched-chain amino acids and their oxo acids did not account for the large negative base excess. Of plasma amino acids, mainly the branched-chain amino acids appeared in the dialyzate, with only modest decreases in the plasma levels. Thus, the plasma pool of branched-chain amino acids was being continously replenished by a large intracellular pool. A similar episode of coma occurring at 18 months of age was not so treated, and ended in death. The dramatic clinical and electroencephalographic response during dialysis and the apparently complete recovery which followed suggests that a diffusible “toxic” factor may be responsible for the coma of maple-syrup-urine disease, but does not itself establish that the branched-chain amino acids or their oxo acids are the etiological agents. The “toxic” factor may have little if anything to do with permanent structural changes and may result in coma and seizures in a brain that is apparently normal histologically. Further evaluation of these therapcutic approaches is warranted, but these exiguous results do not permit unbridled optimism.