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Effects of D-, DL-and L-glutamic acid on chicks
Abstract
Studies were conducted to investigate the effects of D-, DL-, or L-glutamic acid on the chick. Supplementation of levels of L-glutamic acid to an amino acid mixture containing adequate levels of all the indispensable amino acids plus cystine and tyrosine resulted in increased growth up to 10% L-glutamic acid in the diet. Chicks tolerated as much as 15% L-glutamic acid with no growth retardation. Supplementation of D-glutamic acid at levels of 3.75 or 5% resulted in growth depressions of 18 and 38%, respectively, at the end of a 2-week experiment. Significant growth-depressing effects of these levels of D-glutamic acid and 7.5% of DL-glutamic acid were also observed with an amino acid diet as well as an isolated soybean protein diet. The growth-depressing effect was most severe during week 2 of the experiment. Additional vitamins and amino acid supplements failed to reverse the growth-depressing effect. Plasma glutamic acid concentration was not altered by the inclusion of D-glutamic acid in the diet, but generally, plasma free amino acid concentrations were increased. This was especially true of arginine. Free glutamic acid increased in the kidney and was lowered in the liver. Free ammonia was increased in both the liver and kidney when the D form was included in the diet. Implications of these findings are discussed.
... L-glutamic acid, L-alanine and glycine were the amino acid supplements chosen, and DAC was used as the NPN supplement. Maruyama et al. (1975) supplemented chick diets with up to 10% of L-glutamic acid, and did not observe any decline in food consumption. Addition of 3% L-alanine (Maruyama et al., 1975) or 1.6% glycine (Lee et al., 1972) to a semipurified basal diet also did not depress food consumption by chicks. ...
... Maruyama et al. (1975) supplemented chick diets with up to 10% of L-glutamic acid, and did not observe any decline in food consumption. Addition of 3% L-alanine (Maruyama et al., 1975) or 1.6% glycine (Lee et al., 1972) to a semipurified basal diet also did not depress food consumption by chicks. Davis and Austic (1997) did report a decrease in food consumption in chicks over a 9 d period when 4% ...
After obtaining a cDNA clone for chicken hepatic histidase, experiments were conducted to study the regulation of histidase mRNA expression by dietary protein concentrations. Histidase mRNA expression was increased within 3 h when chicks consumed higher levels of dietary protein. Increasing the dietary concentration of histidine did not alter hepatic histidase mRNA expression. The rapid increase in histidase mRNA levels in response to dietary protein intake is similar to the rapid decrease seen in malic enzyme mRNA levels in chicks fed the high protein diets. Glucagon was shown to regulate the mRNA expression of both the enzymes, and could act as a mediator for the effect of dietary protein on histidase and malic enzyme mRNA expression since an increase in dietary protein intake elevated plasma glucagon concentration within 1 h. While histidase mRNA expression seems to be regulated by concentrations of specific amino acids in the diet, malic enzyme mRNA expression seems to be regulated by the total protein or nitrogen level of the diet. Finally, addition of synthetic glutamic acid to a practical corn-soy poultry diet reduced the amount of abdominal fat present in broiler chicks at slaughter. Thesis (Ph. D.)--University of Georgia, 2003. Directed by Adam J. Davis. Includes bibliographical references (leaves 103-116). Electronic reproduction. s
... Compared to D-Asp, the information for D-Glu is limited. Maruyama et al. (1975) reported that chicks derived from mating male New Hampshire with female Single Comb White Leghorn, tolerated nearly 15% of dietary L-Glu with no growth retardation. However, 3.75% of D-Glu levels resulted in growth suppression at the end of the 2-week experiment. ...
D-Amino acids occur in modest amounts in bacterial proteins and the bacterial cell wall, as well as in peptide antibiotics. Therefore, D-amino acids present in terrestrial vertebrates were believed to be derived from bacteria present in the gastrointestinal tract or fermented food. However, both exogenous and endogenous origins of D-amino acids have been confirmed. Terrestrial vertebrates possess an enzyme for converting certain L-isomers to D-isomers. D-Amino acids have nutritional aspects and functions, some are similar to, and others are different from those of L-isomers. Here, we describe the nutritional characteristics and functions of D-amino acids and also discuss the future perspectives of D-amino acid nutrition in the chicken.
... But these early studies clearly illustrate that a certain amount of dietary non-essential amino acids are required (Rechcigl et al., 1957) and that glutamate may be the ideal source. Indeed a number of studies were carried out that claimed dietary glutamate could be considered essential for growth in a variety of species, such as the chicken (Featherson et al., 1962;Maruyama et al., 1975Maruyama et al., , 1976. However, the fact that dietary glutamate is unlikely to be limiting meant that interest in such work was considered of limited practical application and the topic received little attention over the past 30-40 years. ...
Glutamine and glutamate are the most abundant free α-amino acids in the body and comprise between 5 to 15% of dietary protein. Traditionally these amino acids have been classified as non-essential but recently it has been recognized that glutamine may be conditionally essential in hypercatabolic states and a number of benefits have been seen with supplemental glutamine in human clinical studies. In addition, there is evidence for beneficial effects of supplemental glutamine and/or glutamate for the maintenance of optimal health during lactation and for optimal rates of growth in neonatal animals. This paper details inter-organ glutamine metabolism and considers the potential of using supplemental glutamine in domestic animal production.
... Such early studies clearly illustrate that a certain amount of dietary non-essential amino acids are required and that glutamate may be the ideal source (Featherston et al., 1962). A number of studies were carried out that claimed dietary glutamate could be essential for growth in chickens (Maruyama et al., 1975(Maruyama et al., , 1976, and it has been proposed that glutamine is limiting for milk production in the cow (Meijer et al., 1993(Meijer et al., , 1995, but overall, the use of dietary glutamate/glutamine has received very little attention over the past 50 years. But, despite having been classified as non-essential, there is increasing evidence that supplemental glutamate/glutamine may be beneficial, not only in hypercatabolic states, but also in the maintenance of optimal health and maximal rates of growth in healthy animals. ...
Glutamine and glutamate are not considered essential amino acids but they play important roles in maintaining growth and health in both neonates and adults. Although glutamine and glutamate are highly abundant in most feedstuffs there is increasing evidence that they may be limiting during pregnancy, lactation and neonatal growth, particularly when relatively low protein diets are fed. Supplementation of diets with glutamine, glutamate or both at 0.5 to 1.0% to both suckling and recently weaned piglets improves intestinal and immune function and results in better growth. In addition such supplementation to the sow prevents some of the loss of lean body mass during lactation, and increases milk glutamine content. However, a number of important questions related to physiological condition, species under study and the form and amount of the supplements need to be addressed before the full benefits of glutamine and glutamate supplementation in domestic animal production can be realized.
... In contrast, free Glu concentration in plasma did not change among all groups. Previous studies using pigs (Reeds et al., 1996) and chicks (Maruyama et al., 1975) showed that plasma Glu concentration was not altered by dietary Glu. From the aforementioned results, it was concluded that most of the dietary Glu was used for energy production in intestines (Reeds et al., 1996). ...
1. Regulation of meat taste is one effective method for improvement of meat quality. In this study, effects of dietary leucine (Leu) content on taste-active components, especially free glutamate (Glu), in meat were investigated.
2. Broiler chickens (28 d old) were fed on diets with graded dietary Leu content (100, 130 or 150% of Leu requirement in NRC, 1994) for 10 d before marketing. Taste-active components of meat (free amino acids and ATP metabolites) and sensory score of meat soup were estimated.
3. Free Glu content, the main taste-active component of meat, was significantly increased by dietary Leu. Compared with the Leu 130% group, free Glu was increased by 17% in the Leu 100% group. Free Glu of meat tended to decrease in the Leu 150% group. In contrast, inosine monophosphate content in meat did not change among all groups.
4. Sensory evaluation of meat soup from the Leu 100 and 150% groups showed that they had different meat tastes. Sensory scores of overall preference, umami taste and chicken-like taste were significantly higher in the Leu 100% group.
5. These results suggest that dietary Leu content is a regulating factor of free Glu in meat. Decreasing dietary Leu induces an increase in the free Glu content of meat and improves meat taste.
Zur Bestimmung des D-Aminosäureanteils wurde die Methode der Diastereomerenbildung durch Synthese der N-Trifluoracetyl-L-Menthylester weiterentwickelt und auf Hydrolysate von Einzellerproteinen angewandt. Zur Quantifizierung des hydrolyseinduzierten Racemisierungsgrades wurde die gleiche Methode auf das Hydrolysat von Casein angewandt. Mittels dieser Methode konnte das L/D-Verhältnis folgender Aminosäuren ermittelt werden: Ala, Thr, Ser, Val, Leu, Ile, Cys, Met, Pro, Phe, Tyr, Asp, Glu und Trp. Bei den von uns untersuchten Bakterienbiomassen wies nur Glu und in einigen Proben Ala einen gegenüber dem Casein erhöhten D-Anteil auf.
1. The gross composition of Lathyrus sativus was examined, and its use as a foodstuff for growing chicks over time as well as the influence of supplementation with certain amino acid combinations were studied.2. Chemical analyses indicated lathyrus to be high in crude protein with adequate concentrations of most inorganic elements and amino acids except methionine and cystine.3. The performance of growing chicks fed 800 g/kg lathyrus over a four week period was significantly poorer than those given a wheat/ soyabean meal‐based diet (P
The growth rates of young chicks were varied from 0 to 10% per day by manipulation of the adequacy of the amino acid and energy supply. The rates of protein synthesis in the white breast (pectoralis thoracica) muscle and the dark leg (gastrocnemius and peronaeus longus) muscles were estimated by feeding l-[U-(14)C]tyrosine in amino acid/agar-gel diets (;dietary infusion'). This treatment rapidly and consistently produced an isotopic equilibrium in the expired CO(2) and in the free tyrosine of plasma and the muscles. Wholebody protein synthesis in 2-week-old chicks was estimated from the tyrosine flux and was 6.4g/day per 100g body wt. In 1-week-old chicks the rate of protein synthesis was more rapid in the breast muscles than in the leg muscles, but decreased until the rates were similar in 2-week-old birds. Synthesis was also more rapid in fast-growing Rock Cornish broilers than in medium-slow-growing New HampshirexSingle Comb White Leghorn chicks. No or barely significant decrease in the high rates of protein synthesis, in the protein/RNA ratio and in the activity of RNA for protein synthesis occurred in non- or slow-growing chicks fed on diets deficient in lysine, total nitrogen or energy. Thus the machinery of protein synthesis in the young chick seems to be relatively insensitive to dietary manipulation. In the leg muscles, there was a small but significant correlation between the fractional rate of growth and protein synthesis. A decrease in the fractional rate of degradation, however, appeared to account for much of the accumulation of muscle protein in rapidly growing birds. In addition, the rapid accumulation of breast-muscle protein in rapidly growing chicks appeared to be achieved almost entirely by a marked decrease in the fractional rate of degradation.
Studies were conducted on the effects of feeding D-amino acids on growth rate and D-amino acid oxidase (DAAO) in chick kidney.
The crystalline amino acid (AA) diet provided seven amino acids either in the L-form or the DL-form at two concentrations
(DL- or .5 DL-AA diets) with all diets containing equal amounts of L-amino acids. Weight gains of chicks fed the DL-AA diet
were consistently lower than those fed the L- or .5 DL-AA diet. Kidney DAAO activity was significantly higher in chicks fed
either the DL-AA or .5 DL-AA diet as compared with the L-AA diet. Kidney DAAO activity was essentially the same in chicks
fed the DL- and .5 DL-AA diets. Increasing the nonspecific nitrogen in the diet had no effect in alleviating growth depression
of the DL-AA.
1. The effects of dietary branched-chain amino acids (BCAAs) including leucine (Leu), isoleucine (Ile) and valine (Val) on taste-active components, especially free glutamate (Glu), in meat were investigated. 2. Broiler chickens (28 d old) were given varied dietary BCAA levels for 10 d before marketing. Dietary BCAA content ratios were either 100:100:100 (Low Leu group), 150:100:100 (Control group) or 150:150:150 (High Ile + Val group) for Leu:Ile:Val (% of each BCAA requirement according to NRC, 1994). Taste-related components of meat (free amino acids and ATP metabolites) and sensory scores of meat soup were estimated. 3. Free Glu content, the main taste-active component of meat, was significantly increased by dietary BCAA. Compared to the Control group, free Glu content increased by 30% in the High Ile + Val group. However, the inosine monophosphate (IMP) content in meat did not change among groups. 4. Sensory evaluation of meat soups showed that Control and High Ile + Val groups had different meat flavours. The sensory score of overall taste intensity was significantly higher in the High Ile + Val group. 5. These results suggest that dietary BCAA concentrations regulate free Glu in meat. Increasing dietary Ile + Val induces an increase in free Glu content of meat, improves meat taste and is more effective for increasing free Glu content in meat than decreasing dietary Leu level.
GLUTAMINE forms a major fraction of the non-protein nitrogen in the blood plasma of humans and other mammals (Hamilton, 1945; Prescott and Waelsch, 1947; Bessman et al., 1948), and it has been suggested that blood glutamine functions as a non-toxic carrier of ammonia (Meister, 1956), and provides the major source of ammonia excreted in the urine (Van Slyke et al., 1943).
Recently it has been reported that the blood plasma of the chicken also contains considerable glutamine (Olsen et al., 1962) and it seems likely that in the avian species glutamine plays a particularly important part in ammonia metabolism since it is a major contributor of nitrogen during the synthesis of uric acid (Buchanan and Hartman, 1959).
The experiments to be described were designed to provide evidence that the chick uses glutamine as an ammonia carrier in the blood. To this end the response of plasma glutamine to the ingestion…
A series of experiments were conducted to study the effects of excess dietary l-, dl- and d-serine on growth and blood serine concentration in the chick.
Day-old chicks (N.H.×S.C.W.L.) were fed either an l-amino acid diet or a practical diet containing various amounts of serine for two weeks. At the end of the experiment, the
blood was taken for the determination of plasma or serum free serine.
The growth of chicks was significantly depressed when 2.86% l-serine was included in the l-amino acid diet or in the practical diet. Severe growth depression and mortality were observed when dietary l-serine exceeded the 4% level. The addition of excess folic acid, vitamins B6 and B12 (20×N.R.C. requirement) to the practical diet containing 4% l-serine was able to correct partially the growth depression effect caused by excess dietary serine, but was unable to restore
the growth of chicks to the controls. dl-serine was less harmful to the chick at the level corresponding to that of l-serine. d-serine fed at the 4% level had a slight growth inhibition on the chick.
The level of serine in the plasma or serum was increased with the increases of dietary serine content. An extremely high concentration
of serine was observed whenever there was a severe growth depression. d-serine was absorbed and metabolized in the chick.
PROLINE has been considered by nutritionists as a nonessential amino acid for chicks. Its relative abundance in natural proteins made it difficult to determine its role in chick nutrition.
Almquist and Grau (1944) fed a purified diet with and without proline to groups off our chicks. They observed that the birds receiving proline showed an immediate gain in weight, whereas those without it showed a reduced growth rate for four days, but after that time they grew at the normal rate. They classified proline as a dispensable amino acid, but reported that there might be conditions under which the chick did not synthesize it rapidly enough for maximum growth. Benton et al. (1955) reported that when 1% l-proline was added to an amino acid diet containing 0.5% l-proline, there was a very small growth response. Roy and Bird (1959) observed that the addition of 0.5 to 2% l-proline to the…
Various nonessential nitrogen supplements including glycine, glutamic acid, a mixture of glutamic acid and diammonium citrate and a mixture of the nonessential amino acids proportioned as in casein were found to retard the growth of young rats when they were added to diets containing 8.0% of casein and 0.3% of methionine. The effect can be prevented by additions of threonine and tryptophan except in the case of the 7.5% glycine supplement. Increases in the nonessential amino acids fed as supplements and their metabolic derivatives were found in the plasma and muscle tissue. In some instances, the essential amino acids appeared to be decreased. On an isonitrogenous basis, glycine supplementation caused the greatest reduction in growth rate and produced the greatest changes in plasma amino acid concentrations.
The injection into the normal or adrenalectomized rat of α-aminoisobutyric acid caused the loss from the liver within 2 h of to of its normal content of the various neutral amino acids. At the same time a profound aminoaciduria was produced, including the cationic as well as the neutral amino acids. Indeed, the early effect on lysine excretion was exceptionally strong, although that on cystine later became even stronger. The N-methyl derivative of α-aminoisobutyric acid produced an aminoaciduria limited to proline and hydroxyproline, but the action on the retention of neutral amino acids by the liver was still general. Two other analogs, α,α diethylglycine and α,α-dicyclopropylglycine, structurally designed to minimize their reactivity with known transport systems, showed weak and negligible effects, respectively, on both the hepatic retention and the renal excretion of amino acids. These associations, together with the metabolic inertness of the test substances, indicate that the above effects arise from competition for transport. Inclusion of α-aminoisobutyric acid in the diets of young rats inhibited their growth in approximate correspondence to the decrease in food intake.
l-Cystine, dl-tryptophan, dl-tyrosine, l-histidine, glycine, and d-glutamic acid are more toxic in the riboflavin-deficient rat than in the rat receiving this vitamin.
The addition of 1% dl-phenylalanine and 1% l(-) tyrosine to a purified diet containing 10% casein produced growth retardation and external lesions. Phenylalanine is converted to tyrosine in the animal and so may add to the effect of the tyrosine. The addition of relatively large amounts of nicotinic acid or l(-)tryptophane will appre ciably alleviate the deleterious effects of these amino acids.
The metabolism of glycine and serine in chick and pigeon livers was studied with mitochondria and cell homogenates. The avian liver mitochondria actively catalyzed the cleavage of glycine into methylene-THF, 2CO2, and ammonia, but failed to appreciably catalyze CO2 formation from the α-carbon of glycine. CO2 formation from the β-carbon of serine was also very small in either the mitochondrial or the homogenate system, whereas the carboxyl carbon of serine was actively decarboxylated. In the avian livers L-serine dehydratase was apparently absent and the activity of 10-formyl-THF: NADP+ oxidoreductase was extremely low, if not nil. However, chick liver, but not pigeon liver, was shown to contain an enzyme with the characteristics of D-serine dehydratase, although its exact nature remains to be clarified. The one-carbon compound(s), derived from either glycine or serine in the avian livers was utilized largely for the synthesis of uric acid. With the soluble fraction of avian livers, the yields of 14C-purine from serine-3-14C were about two times larger than those from serine-1-14C. When 14C-glycine alone was employed as the source of both the one-carbon compound and glycine, the yields of 14C-hypoxanthine, from 14C-glycine, especially from glycine-2-14C, were significantly increased by the addition of mitochondria to the soluble liver fraction, and under these reaction conditions the ratio of the yields of 14C-hypoxanthine from glycine-1-14C and 2-14C rose to 1:2.3. It was assumed that the glycine cleavage system in the mitochondria plays an important role as a one-carbon donating system for purine synthesis in the avian liver. Although the avian liver mitochondria could catalyze glycine synthesis as the reverse of the glycine cleavage reaction, the contribution, if any, of the synthetic reaction to purine synthesis seemed to be insignificant.
Some effects of feeding chicks D- or L-dispensable amino acids for 2 weeks in three types (practical, purified and amino acid) of complete diets have been studied. Growth was depressed significantly by 1.5% of D-alanine, but not by 2% of L-alanine or 2% of D-serine. When the amino acid diet contained 4.4% of other D-amino acids, 1.25% of D-alanine also caused growth depression. Two percent of D-aspartic acid depressed growth significantly, whereas 6% of L-aspartic acid did not. When D-aspartic acid was replaced by L-aspartic acid after 1 week, growth rate and feed consumption increased rapidly and ap proached values for control birds. Plasma aspartic acid concentration, which was high when D-aspartic acid was fed returned to near normal within 2 days. Plasma free aspartic acid concentration increased to 25-fold the normal value within 3 days when the D-aspartic acid was substituted for the L-form after 1 week. A high plasma free aspartic acid concentration was maintained in chicks fed 2% of D-aspartic acid. L-Aspartic acid at 3% in the diet did not elevate plasma aspartic acid concentration. High protein (35% and 50% ) diets, amino acid supplements and additional vitamins all failed to overcome the growth- depressing effect of D-aspartic acid. J. Nutr. 102: 1441-1452, 1972.
1. Hypertryptophanaemia, hypertryptophanuria and to a lesser degree a generalized hyperaminoaciduria were observed in phenylketonuric patients receiving certain commercial low-phenylalanine diets containing DL-tryptophan.
2. The generalized hyperaminoaciduria was associated with the ingestion of acid hydro-lysates of protein, but not with the ingestion of enzymic hydrolysates or D-tryptophan.
3. Alanine recovered from the urine of these treated patients had a D-isomer content of approx. 50%. This amount of urinary D-alanine could be derived from the ingestion of an acid hydrolysate of protein in which the amino acids had racemized to the extent of 2–3%.
The injection into the normal or adrenalectomized rat of α-aminoisobutyric acid caused the loss from the liver within 2 h of 1 3 to 2 3 of its normal content of the various neutral amino acids. At the same time a profound aminoaciduria was produced, including the cationic as well as the neutral amino acids. Indeed, the early effect on lysine excretion was exceptionally strong, although that on cystine later became even stronger. The N-methyl derivative of α-aminoisobutyric acid produced an aminoaciduria limited to proline and hydroxyproline, but the action on the retention of neutral amino acids by the liver was still general. Two other analogs, α,α diethylglycine and α,α-dicyclopropylglycine, structurally designed to minimize their reactivity with known transport systems, showed weak and negligible effects, respectively, on both the hepatic retention and the renal excretion of amino acids. These associations, together with the metabolic inertness of the test substances, indicate that the above effects arise from competition for transport. Inclusion of α-aminoisobutyric acid in the diets of young rats inhibited their growth in approximate correspondence to the decrease in food intake.
The addition of 0.5% α-aminoisobutyric acid (AIB), a presumably nonmetabolizable amino acid, to a casein basal diet supplemented with graded levels of L-arginine·HCl caused an accumulation of free arginine and a depression of free ornithine in both plasma and muscle of chicks, and also altered the levels of some other amino acids. The differential effect on free amino acids was more pronounced in muscle than in plasma. Injection of AIB into the breast muscle of chicks fed the casein diet supplemented with 3% L-arginine·HCl gave an effect on arginine, ornithine and other amino acids similar to that given by oral feeding of AIB. Further observations of significance were that the weight gain and feed efficiency of chicks fed the casein basal diet were improvd by supplementation with AIB, and that kidney arginase activity was greatly depressed when AIB was fed. Arginine metabolism was also affected by AIB in chicks fed a basal diet based on wheat gluten supplemented with arginine, but the growth response to AIB supplementation found with the casein diet was not observed. Possible mechanisms of the influence of AIB on arginine metabolism are discussed in relation to the experimental findings.
Cycloleucine (1-aminocyclopentanecarboxylic acid) administration in cancer patients resulted in a reversible marked aminoaciduria consisting predominantly of cystine, ornithine, lysine, and arginine, with only minor elevations of other amino acids. Plasma levels of amino acids were essentially unchanged except for slight decreases in ornithine and lysine. This aminoaciduria is most likely due to a blockage by the drug of the renal tubular reabsorption of cystine, ornithine, lysine, and arginine, resulting in an aminoaciduria of the type seen in cystinuria.
In the normal fasted dog ammonia was added to the blood in the kidneys and portal bed and was removed in the liver. Glycine given intravenously resulted in ammonia release into the blood in the liver and additional ammonia release by the kidneys, with concomitant rise in the arterial ammonia concentration. At high arterial levels ammonia was removed in the extremities and head. l-Arginine injected intravenously during the glycine infusion produced an abrupt cessation of ammonia release by the liver and caused this organ to remove ammonia from the incoming blood. A rapid fall in arterial ammonia concentration occurred. Arginine did not affect ammonia release or removal by any organ tested other than the liver. The possible therapeutic significance of the capacity of l-arginine to prevent ammonia release at an important site of ammonia formation is discussed.
The toxicity of 19 amino acids when fed individually in excess (5% level) in a low-protein diet was studied with weanling rats. With the exception of alanine, all amino acids tested produced depressions in growth to varying degrees. Methionine produced the severest growth depressions followed in decreasing order by tryptophan, DL-aspartic acid, histidine, tyrosine, phenylalanine, cystine, leucine, valine, isoleucine, glycine, asparagine, arginine, L-aspartic acid, lysine and threonine. Glutamic acid, proline and serine produced only slight growth depressions.
Results of studies on the isomers of several amino acids indicated that the D-isomers usually produced less inhibition in growth than the corresponding L-form. DL-Aspartic acid, however, produced greater detrimental effects than L-aspartic acid.
The growth depression of the several amino acids studied could be partially or completely prevented by supplements of protein to the diet. The degree of toxicity of the amino acids was dependent also upon the specific protein fed the animals.
L-Cystine at a level of 5% in a low-protein diet depressed growth and produced some deaths. When the casein in the high-cystine diet was increased to a level of 36%, the number of deaths was greatly increased. When lactalbumin was fed in place of casein, however, no deaths occurred and growth was nearly normal.
Supplements of leucine or of hemoglobin to a corn grain basal diet produced a severe depression in growth. The effect was partially-to-completely reversed by supplements of isoleucine.
Analyses of the plasma usually demonstrated high values for free amino acid content of the amino acid supplemented in excess in the diet. However, the toxicity of several amino acids did not appear to be directly related to their plasma concentration.
• Levels of methionine only slightly above those necessary for growth depressed the growth of rats fed limiting amounts of vitamin B6. Vitamin B6 counteracted the effects of moderate amounts of methionine. When the diet contained 2.5% of methionine, high levels of the vitamin failed to restore growth. D-, L- and DL-methionine and DL-homocystine were approximately equivalent in depressing growth; cystine did not depress growth.
• Acrodynia was aggravated by moderate amounts of methionine (D-, L- or DL-isomers), and by homocystine.
• Glycine, alanine, serine, cystine, threonine, and additional B vitamins did not affect growth when moderate levels of methionine were added to diets limiting or deficient in vitamin B6.
• When the ration contained 1.0% of added methionine, the three forms of vitamin B6 were approximately equal in promoting growth; in some experiments the most active form of the vitamin appeared to be pyridoxal.
• The consumption of pyridoxine decreased the excretion of free methionine in the urine of rats fed moderate amounts of the amino acid. Dietary methionine did not affect the concentration of vitamin B6 in the blood or liver of rats.
• Addition of 3, 6, and 9% glycine to vitamin B12-deficient diets caused a growth depression and increased mortality in growing chickens.
• Both vitamin B12 and folic acid function in counteracting this toxicity; however, B12 is somewhat more effective.
• Addition of 6 or 9% glycine to the diet increased blood uric acid levels. Folic acid tended to decrease these high levels of uric acid in the blood.
• Vitamin B12 tends to increase the level of uric acid in the blood of young chickens.
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