Acid loads induced by the detoxification of plant secondary metabolites do not limit feeding by common brushtail possums (Trichosurus vulpecula)

We fed common brushtail possums artificial diets containing a buffer and the plant secondary metabolite (PSM), orcinol, to test the hypothesis that organic acids, common products of PSM metabolism, limit feeding by common brushtail possums (Trichosurus vulpecula). We introduced several diets containing orcinol and a buffer (urinary alkalising agent) over a course of three experiments. A diet containing 2% orcinol (wet matter) caused possums to reduce their food intake immediately, but feeding returned to normal 1–2 days later. Even though possums excreted strongly acidic urine (pH 5.1) and had perturbed nitrogen metabolism, they maintained their food intake and body mass until the experiment terminated 9 days after the introduction of orcinol. Possums ate 52% less when the basal diet contained 4% orcinol. As expected, the acid loads caused a change in the composition of urinary nitrogen with possums excreting more ammonium than urea and a large amount of unidentified nitrogenous material. Supplementing the diet containing orcinol with buffer neutralised the metabolic acid load and partly restored normal nitrogen metabolism, but did not restore feeding. Also, animals eating orcinol excreted normal amounts of 3-methylhistidine, indicating no increase in muscle protein catabolism. This suggests that a limitation to the rate of detoxification or toxicosis, rather than acid loads, limits the ingestion of acid-inducing PSMs.     

Effects of dietary protein and amino acid levels on the expression of selected cationic amino acid transporters and serum amino acid concentration in growing pigs

The absorption of lysine is facilitated by leucine, but there is no information regarding the effect of crude protein, lysine and leucine levels on the expression of cationic amino acid transporters in pigs. Therefore, an experiment was conducted with 20 pigs (14.9 +/- 0.62 kg initial body weight) to evaluate the effect of two protein levels, and the content of lysine, threonine, methionine and leucine in low crude protein diets on the expression of b(0,+) and CAT-1 mRNA in jejunum, Longissimus dorsi and Semitendinosus muscles and serum concentration of amino acids. Treatments were as follows: (i) wheat-soybean meal diet, 20% crude protein (Control); (ii) wheat diet deficient in lysine, threonine and methionine (Basal diet); (iii) Basal diet plus 0.70% L-lysine, 0.27% L-threonine, 0.10% DL-methionine (Diet LTM); (iv) Diet LTM plus 0.80% L-leucine (Diet LTM + Leu). Despite the Basal diet, all diets were formulated to meet the requirements of lysine, threonine and methionine; Diet LTM + Leu supplied 60% excess of leucine. The addition of lysine, threonine and methionine in Diet LTM increased the expression of b(0,+) in jejunum and CAT-1 in the Semitendinosus and Longissiums muscles and decreased CAT-1 in jejunum; the serum concentration of lysine was also increased (p < 0.01). Further addition of L-leucine (Diet LTM + Leu) decreased the b(0,+) expression in jejunum and CAT-1 in the Longissimus dorsi muscle (p < 0.05), increased the serum concentration ofleucine and arginine and decreased the concentration of isoleucine (p < 0.05). Pigs fed the Control diet expressed less b(0,+) in jejunum, and CAT-1 in the Semitendinosus and Longissiums muscles expressed more CAT-1 in jejunum (p < 0.05) and had lower serum concentration ofisoleucine, leucine and valine (p < 0.05), but higher lysine concentrations (p < 0.01) than those fed Diet LTM. These results indicated that both, the level and the source of dietary amino acids, affect the expression of cationic amino acid transporters in pigs fed wheat-based diets.     

Dietary supplements of mixtures of indispensable amino acids lacking threonine, phenylalanine or histidine increase the activity of hepatic threonine dehydrogenase, phenylalanine hydroxylase or histidase, respectively, and prevent growth depressions in chicks caused by dietary excesses of threonine, phenylalanine, or histidine*

Experiments were carried out to determine whether the addition of a mixture of indispensable amino acids (IAA) lacking in threonine, phenylalanine or histidine, respectively, to a nutritionally complete diet would increase the hepatic activities of the rate-limiting enzymes for catabolism of threonine, phenylalanine or histidine and prevent the adverse effects of the amino acid on growth when the dietary level of the amino acid is excessive. Week old Leghorn chicks were fed semi-purified diets containing 19% crude protein to which were added no IAA supplement or 10% crude protein from an IAA mix and 5 graded levels of either L-threonine, L-phenylalanine or L-histidine in a 2 x 5 factorial arrangement of treatments. Each amino acid was investigated in a separate experiment involving four replicate pens (seven chicks each) per diet. Weight gains and feed consumptions were determined on the fourteenth day of each experiment. The groups receiving no excess, and 1.0% or 2.0% excesses of amino acids were sampled on the fifteenth day for enzyme activities and plasma amino acid concentrations. Weight gain and/or feed consumption were lower, and plasma concentrations of threonine, phenylalanine and histidine were higher, in chicks receiving 1.5 to 2.0% dietary additions of threonine, phenylalanine, and histidine, respectively, than in chicks that did not receive these amino acids. Chicks that received the amino acids in diets that also contained the IAA supplement had better growth and feed consumption, lower plasma concentrations of threonine, phenylalanine or histidine, higher plasma concentrations of other indispensable amino acids, and higher activities of threonine dehydrogenase, phenylalanine hydroxylase, and histidase than chicks receiving excess amino acids in the absence of IAA supplements. We conclude that the dietary level of protein, not the dietary level of individual amino acids, is the primary determinant of the activity of amino acid degrading enzymes in liver. The increased activity of these enzymes may be the mechanism by which dietary protein alleviates the adverse effects of excessive levels of individual amino acids.     

Meat meal in the diet of the early-weaned pig IV. The supplementation of diets with tryptophane,lysine and methionine

Two experiments were conducted with 72 pigs between 28 and 56 days of age to study the effect of tryptophane supplementation on their performance when fed on diets containing wheat and meat meal.In the first experiment, pigs were fed on a basal diet (Diet 1) or on the same diet supplemented with calcium dihydrogen phosphate (Diet 2), bone meal (Diet 3) or bone meal plus tryptophane (Diet 4), all to 3.1% calcium. The weight gains of the pigs (315 g day^?1) fed on Diet 3 were significantly lower than that of the pigs fed on the other three diets (363 g day^?1). The feed conversion ratios showed a similar trend. Diet 3 contained 0.16% tryptophane while the other diets contained 0.18–0.19% tryptophane. The crude protein, lysine and methionine contents of all diets were similar.In the second experiment, a basal diet containing meat meal and bone meal was supplemented with tryptophane, lysine plus methionine or all three amino acids. Feed intake was increased by all amino acid supplements. Weight gains were improved significantly (57%) by the addition of all three amino acids to the diets, but the improvements due to tryptophane alone (28%) or methionine plus lysine (35%) were not significant. Tryptophane supplementation alone or with lysine plus methionine increased the nitrogen retention of the pigs.It was concluded that the requirement for tryptophane of pigs between 28 and 56 days of age was greater than 0.16% of diets containing wheat and meat meal.     

The importance of green seed in the nitrogen nutrition of the Zebra Finch Taeniopygia guttata

Abstract Australian grass-finches are widely reported to consume large quantities of green seed when it becomes available, and the opportunistic breeding of wild Zebra Finches in the arid zone has been correlated with the occurrence of rain. In this study, green and ripe seeds were harvested from seven pasture and weed grasses grown in experimental plots and, along with three cereal flours and whole-egg powder, were analysed for the amino-acid composition of their protein. The relative levels of ten amino acids essential in the diets of growing birds were compared between samples using a cluster analysis dendrogram generated from Raabe's Similarity Index. The protein of all green seeds clustered with whole egg, and away from all but one of the ripe seeds and seed products. Green and ripe seed profiles were found to be significantly different by a two-sample multivariate test of significance (Hotelling's T²). Histidine, lysine, phenylalanine and threonine were the amino acids most different. Of these four amino acids, lysine and threonine (along with methionine) were potentially limiting in ripe seeds when compared with whole-egg protein. In green seeds, lysine was only marginally limiting, threonine was no longer limiting, but methionine was still limiting when compared with whole-egg protein. These results indicate that the benefit of green vs ripe seed in the diet of breeding Zebra Finches is partly a higher level of the limiting essential amino acid, lysine, and partly a higher intake and throughput of soft green seed and consequent greater extraction of limiting essential amino acids.     

The importance of dietary amino acids on the reproduction and longevity of adult Dacus oleae (Gmelin) (Diptera Tephritidae)

When the amino-acid mixture of an effective chemically defined diet was replaced by single amino acids, keeping the total nitrogen at the same level, the egg production of Dacus oleae was minimal with all the 19 amino acids tested. Male survival was adversely affected by the amino acids : alanine, aspartic acid, glutamic acid, glycine, hydroxyproline, lysine, serine and tyrosine, while female survival was shortened when the amino acids : glycine, hydroxyproline and lysine were added. The creation of amino-acid imbalances, by deleting the 19 amino acids individually, from the complete amino-acid mixture, showed that the amino acids : arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, serine, threonine, tryptophane and valine were indispensable to the adult Dacus oleae flies, as far as egg production is concerned. Survival of the male flies was significantly shortened when the amino acids : alanine, hydroxyproline and tryptophane were omitted. Significant differences in longevity between males and females were scored, when the amino acids : alanine, aspartic acid, cystine, glycine and tryptophane, were omitted.     

Effects of Sulfur-containing Amino Acids and Glycine on Plasma Cholesterol Level in Rats Fed on a High Cholesterol Diet

The effects of the addition of individual amino acids on methionine-induced hypercholesterolemia (experiment 1), and the interacting effects of dietary protein level and sulfur-containing amino acids and glycine on plasma cholesterol concentration (experiment 2) were studied in growing rats fed on a high cholesterol diet. In experiment 1, rats were fed on a 25% casein-0.75% methionine (25CM) diet containing 2.5% of individual amino acids for 2 weeks. Methionine-induced hypercholesterolemia was prevented by the concurrent addition of glycine or serine, but the other amino acids tested (alanine, threonine, leucine, phenylalanine, lysine, arginine, and glutamic acid) had no effect. Histidine rather enhanced the hypercholesterolemia. In experiment 2, rats were fed on a 10%, 25%, or 50% casein diet containing 0.75% methionine, 0.60% cystine, 0.63% taurine, 2.5% glycine, or 0.75% methionine +2.5% glycine for 3 weeks. Dietary addition of 0.75% methionine increased the plasma cholesterol concentration for the 25% and 50% casein diets, but it decreased the plasma cholesterol for the 10% casein diet. When the addition level of methionine was doubled in the 10% casein diet, the plasma cholesterol concentration was significantly higher for the 1.5% methionine-added diet than for the 0.75% methionine-added diet. Cystine and taurine lowered plasma cholesterol for all dietary casein levels. Methionine-induced hypercholesterolemia with 25% and 50% casein diets was prevented by the glycine supplementation. These data suggest that sulfur-containing amino acids and glycine are important in plasma cholesterol regulation.     

Interspecific and seasonal dietary differences of Himalayan thar, chamois and brushtail possums in the central Southern Alps, New Zealand

Himalayan thar or tahr (Hemitragus jemlahicus), Alpine chamois (Rupicapra rupicapra) and brushtail possums (Trichosurus vulpecula) are native to the Himalaya, Europe and Australia, respectively, but are now sympatric in parts of the central Southern Alps, New Zealand. All three species are managed as pests by the Department of Conservation. We analysed the diets of 246 thar, 78 chamois and 113 possums collected in the central Southern Alps during 1988–1996. The diets of thar and chamois strongly overlapped, but thar ate more grasses and less herbs and woody plants than chamois. The diet of possums differed from the diets of thar and chamois, containing a different suite of herbs and almost no grasses. The diets of thar, chamois and possums varied seasonally. Contrary to expectation, the diets of adult male and female thar were similar during the period when they are spatially segregated (October–May). Chamois sampled outside the thar range ate more species than those sampled inside the thar range, suggesting that the presence of thar modifies the diet of chamois. If managers wish to protect the dominant Chionochloa snow tussocks then thar should be controlled; chamois should be controlled to protect herbs such as Ranunculus spp.; and possums should be controlled if Podocarpus nivalis or Muehlenbeckia axillaris need to be protected. However, managers need to be aware of the potential for chamois to increase in abundance, at least in some sites, if thar are controlled to low abundance, and that this could lead to different impacts on plant populations.     

Amino acid imbalance in the liquid-fed lamb.

Eleven Poll Dorset times Merino crossbred female lambs 4 weeks of age were trained to suck liquid diets from bottles. In three separate experiments liquid diets providing 14-2% (expt 1) 10-6% (expt 2) or 8-0% (expt 3) of gross energy as protein and amino acids were fed. Responses in voluntary intake, growth rate and changes in plasma amino acid concentrations were studied when complete or incomplete mixtures of amino acids were added to the liquid diet. These mixtures supplied either: (1) all amino acids in quantities to bring the total of protein plus amino acids to provide more than 20% of dietary gross energy, the amino acids being provided in proportions estimated to meet adequately the lamb's requirements ('complete'); or (2) as the same total amount of amino acids but with the amino acid supplement devoid of threonine ('low-threonine', expts 1 and 2) or isoleucine ('low isoleucine', expt 3). In experiment 1, there was no food intake or growth depression after feeding the amino acid mixture lacking threonine. In both experiments 2 and 3, voluntary food intake was depressed to about 50% of that observed in lambs fed the low protein diet, when the amino acid mixture devoid of threonine or of isoleucine, respectively, was fed. Addition of the missing amino acid to the low threonine and low isoleucine diets resulted in recovery of voluntary intake in experiments 2 and 3 respectively, but no significant improvement above that found after feeding the low protein (basal) diet. In experiments 1 and 2, after feeding the low threonine diet the threonine concentration in the blood plasma decreased markedly, while concentrations of total amino acids were elevated. Although there was no improvement in growth or food intake, the feeding of the diet containing the complete amino acid mixture resulted in an elevation of all essential amino acids including threonin. Similarly in experiment 3, plasma isoleucine concentration decreased in the lambs fed the isoleucine imbalanced diet. Results indicate that the suckled, preruminant lamb exhibits sensitivity to dietary amino acid imbalance, in a manner analogous to that found in simple-stomached animals. These results also clearly illustrate a depression in food intake associated with the deletion of a specific essential nutrient from the diet of the lamb.     

Meat meal in the diet of the early-weaned pig. II. Amino acid supplementation

One hundred and twenty pigs, initially 4–5 kg liveweight, were fed on wheat-based diets supplemented with meat meal and amino acids in two experiments, each of 4 weeks duration.In the first experiment, the supplementation of a normal meat meal diet with lysine and methionine increased the feed intake and weight gains of the pigs by 15 and 18%, respectively. Nitrogen retention was increased by 30%. Tryptophane gave a similar response to lysine and methionine.In the second experiment, a 21% crude protein basal diet was similar to the basal diet of the first experiment but it contained 1.02% lysine and 0.50% methionine plus cystine, compared to 0.90 and 0.51%, respectively, in the first experiment. Lysine and methionine supplementation of the diet did not significantly improve the performance of the pigs in the second experiment, but the supplementation of the diets with 0.08% tryptophane and lysine and methionine increased weight gains and feed intakes and decreased urea content of the blood plasma. The 21% crude protein diet contained 0.15% tryptophane.Increasing the crude protein content of diets from 18 to 24% by increasing their meat meal content increased the daily weight gains from 190 to 276 g.     

Amino acid supply and protein metabolism in Ehrlich ascites tumour cells. 1. Identification of limiting amino acids

The uptake and intracellular accumulation of an amino acid mixture by incubated Ehrlich ascites tumour cells was studied. The composition of the amino acid mixture simulated that of mouse intraperitoneal fluid and amino acid uptake was studied over a range of concentrations between 0.0 (no added amino acids) and 10.0-times intraperitoneal concentrations. For most amino acids uptake into cells and intracellular accumulation occurred as concentrations were increased up to 6.0-times the intraperitoneal concentrations; further increases in external amino acid concentrations did not increase concomitantly with intracellular concentrations. These data, when analysed indicated a net protein synthetic rate of 20% d-1 and that the rate of protein synthesis may be limited by the availability of the amino acids lysine, threonine and methionine.     

The effects of added sulphur amino acids, threonine and an ideal amino acid ratio on nitrogen metabolism in mature, overweight dogs

The objectives of this study were to investigate the effects of added essential amino acids in conjunction with a dietary lysine/MJ of 0.72 on nitrogen (N) metabolism in dogs. Treatments were; a control diet, a diet that provided an ideal amino acid profile (IAA), a diet with added total sulphur amino acids (TSAA), and a diet with added TSAA and threonine (TT). Diets were fed to eight overweight, mature, female hounds using a replicated 4 x 4 Latin Square design. Food intake was similar across treatments, however, food N intake was higher (p < 0.001) for TSAA than control, IAA or TT. Nitrogen absorbed was higher (p < 0.01) for TSAA than IAA and control. Urea N excretion was greater for control than TT (p < 0.05). Urine N excretion did not differ between diets. There were no differences in digestibility or N retention of diets. There were no differences in protein turnover, synthesis, or degradation. Blood metabolites were within normal ranges and did not differ due to dietary treatment. Based on the measurements made in this study, there is no benefit for added TSAA, TT or additional EAA in diets for mature dogs formulated to provide a 0.72 g lysine/MJ ME ratio.     

The mouse liver content of carbonic anhydrase III and glutathione S-tranferases A3 and P1 depend on dietary supply of methionine and cysteine

The contents of glutathione S-transferase (GST) subunits, carbonic anhydrase III (CAIII), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and a 230 kDa protein are affected by protein deprivation in mouse liver. In order to know if particular amino acids control these contents, the effects of feeding for 5 days with diets containing different amino acids were examined. After an exploration using SDS-PAGE analysis, the action of selected diets was further examined by distinct techniques. The 230 kDa protein was identified as fatty acid synthase (FAS) by both mass spectrometry and amino acid sequence analyses. Dietary tests showed that: (1) a protein-free diet (PFD) increased the content of glutathione S-transferases P1 and M1, and glyceraldehyde-3-phosphate dehydrogenase, while the content of glutathione S-transferase A3, fatty acid synthase and carbonic anhydrase III decreased; (2) a protein-free diet having either methionine or cysteine preserved the normal contents of glutathione S-transferases P1, A3, M1 and carbonic anydrase III; (3) a protein-free diet having threonine preserved partially the normal contents of glutathione S-transferases P1, A3, M1 and carbonic anhydrase III; (4) a protein-free diet having methionine, threonine and cysteine prevented in part the loss of fatty acid synthase; and (5) the glyceraldehyde-3-phosphate dehydrogenase content was controlled by increased carbohydrate level and/or by lower amino acid content of diets, but not by any specific amino acid. These data indicate that methionine and cysteine exert a main role on the control of liver glutathione S-transferases A3 and P1, and carbonic anhydrase III. Thus, they emerge necessary to prevent unsafe alterations of liver metabolism caused by protein deprivation.     

Influence of Protein Source on Growth-depressing Effect of Excess Amino Acids in Young Rats

The influence of protein quality on the growth-depressing effect of excessive amount of 12 individual essential and semiessential amino acids was examined. Growing rats were fed for 3 weeks diets containing either 10.5% egg albumin or 11.6% wheat gluten (equivalent to the protein content of a 10% casein diet) supplemented with 5% of each of the l-amino acids. In general, the pattern of growth depression produced by the addition of excess amino acids to the egg albumin or the wheat gluten diet was similar to that of the case of casein diet obtained previously under the same experimental conditions. However, the extent of these effects was dependent not only upon the kind of amino acid supplemented with but also upon the source of protein used, and the depressing effect of each of excess amino acids added to the wheat gluten diet was usually severer than those added to casein and egg albumin diets. No evidence was noted of any striking changes in the liver protein and nucleic acid concentrations by either diets, but total liver protein, RNA and DNA contents were decreased in some amino acid groups of the egg albumin diet and in all amino acid groups of the wheat gluten diet except the lysine addition. The free amino acid level in plasma generally showed extreme elevation for the amino acid supplemented in excess in the diet, and in most cases the extent of the elevation was correlated with the growth depression.     

Enhanced levels of free and protein-bound threonine in transgenic alfalfa (Medicago sativa L.) expressing a bacterial feedback-insensitive aspartate kinase gene

Threonine, lysine, methionine, and tryptophan are essential amino acids for humans and monogastric animals. Many of the commonly used diet formulations, particularly for pigs and poultry, contain limiting amounts of these amino acids. One approach for raising the level of essential amino acids is based on altering the regulation of their biosynthetic pathways in transgenic plants. Here we describe the first production of a transgenic forage plant, alfalfa (Medicago sativa L.) with modified regulation of the aspartate-family amino acid biosynthetic pathway. This was achieved by over-expressing the Escherichia coli feedback-insensitive aspartate kinase (AK) in transgenic plants. These plants showed enhanced levels of both free and protein-bound threonine. In many transgenic plants the rise in free threonine was accompanied by a significant reduction both in aspartate and in glutamate. Our data suggest that in alfalfa, AK might not be the only limiting factor for threonine biosynthesis, and that the free threonine pool in this plant limits its incorporation into plant proteins.     

THE EFFECT OF ELEVATED AMINO ACIDS ON AMINOTRANSFERASE LEVELS IN BRAIN AND LIVER OF THE MOUSE

Abstract— Adult mice were fed standard diets that were enriched with selected amino acids, i.e. 3% methionine, 6% valine, or 8% lysine. These diets caused the following changes in the amino acid pool of the brain measured at 7 and 21 days. The high methionine diet resulted in 50-fold higher levels of methionine and cysteine and somewhat lower levels of serine and glutamine. The valine and lysine-enriched diets also caused 2- to 4-fold increases in valine and lysine contents of brain, respectively. In spite of the large changes in amino acid levels, however, there were essentially no changes in aspartate: α-ketoglutarate, alanine: α-ketoglutarate, ornithine: α-ketoglutarate, methionine: α-ketoglutarate, and the branched chain aminotransferase activities of brain 3, 10, and 21 days after the onset of the dietary regimen. In contrast, these diets produced significant changes in some of these enzyme activities in liver. Changes in liver included a 2-fold increase in ornithine and alanine aminotransferase activities with the methionine-enriched diet. Liver ornithine aminotransferase activity also increased slightly in animals fed the valine-enriched or lysine-enriched diet.     

Submerged culture conidial germination and conidiation of the bioherbicideColletotrichum truncatum are influenced by the amino acid composition of the medium

Summary Submerged culture experiments were conducted to determine the optimal nitrogen source for rapidly producing conidia of the bioherbicide,Colletotrichum truncatum. Germination ofC. truncatum conidial inocula in submerged culture occurred most rapidly (>95% in 6 h) in media provided with a complete complement of amino acids. When (NH₄)₂SO₄, urea, or individual amino acids were provided as the sole nitrogen source, conidial germination was less than 20% after 6 h incubation. Conidia production was delayed inC. truncatum cultures grown in media with urea or individual amino acids as nitrogen sources compared to cultures supplied with Casamino acids or complete synthetic amino acid nitrogen sources. The use of methionine, lysine, tryptophan, isoleucine, leucine or cysteine as a sole nitrogen source severely inhibitedC. truncatum conidia production. Media with synthetic amino acid mixtures less these inhibitory amino acids produced significantly higher conidia yields compared to media with amino acid mixtures containing these amino acids. When various amounts of each individual inhibitory amino acid were added to media which contained amino acid mixtures, cysteine and methionine were shown to be most effective in reducing conidiation. An optimal nitrogen source forC. truncatum conidiation in submerged culture should contain a complete mixture of amino acids with low levels of cysteine, methionine, leucine, isoleucine, lysine and tryptophan for rapid conidiation and optimal conidia yield.The mention of firm names or trade products does not imply that they are endorsed or recommended by the US Department of Agriculture over other firms or similar products not mentioned.     

How well can common brushtail possums regulate their intake of Eucalyptus toxins?

We studied factors affecting the ability of common brushtail possums (Trichosurus vulpecula) to regulate their intake of a dietary toxin, jensenone, extracted from Eucalyptus leaves. Increasing concentrations of jensenone in the diet led to a dose-dependent decrease in food intake best described as an exponential decay. Animals that had not previously been exposed to jensenone ate significantly more when first offered food containing the compound than on subsequent days. However, when offered the same amount of food in a number of portions throughout the night, naive animals ate significantly less than animals offered the total meal at once. When offered food containing jensenone over a 13-day period, the animals' intake varied cyclically with relatively high food intakes followed by relatively low intakes. Furthermore, animals that were exposed to cold conditions (4 degrees C) ate more than those maintained at 18 degrees C but this difference was abolished when jensenone was included in the diet. We interpret these results as showing that regulation of toxin intake by common brushtail possums depends on learned responses that can override other important influences on feeding.     

Nutritional improvement of the aspartate family of amino acids in edible crop plants

Summary Plants are the primary source of protein for man and livestock, however, not all plants produce proteins which contain a balance of amino acids for the diet to ensure proper growth of livestock and humans. Alteration of the amino acid composition of plants may be accomplished using techniques of molecular biology and genetic engineering. Genes encoding key enzymes regulating the synthesis of lysine and threonine have been cloned from plants andE. coli and are available for modification and transformation into plants. Genes encoding seed storage proteins have been cloned and modified to encode more lysine residues for developing transgenic plants with higher seed lysine. Genes encoding seed storage proteins naturally higher in methionine have been cloned and expressed in transgenic plants, increasing methionine levels of the seed. These and other approaches hold great promise in their application to increasing the content of essential amino acids in plants.Abbreviations: AK = aspartokinase; HSDH = homoserine dehydrogenase; DS = dihydrodipicolinic acid synthase; AEC = S-(2-aminoethyl)-L-cysteineMention of trademark, proprietary product or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may be suitable.     

Liver Nonprotein Sulfhydryl and Taurine Concentrations,and Fat Content of Rats Fed a Low Protein Diet Supplemented with Sulfur-containing Amino Acids

The relative excess of some catabolites of sulfur-containing amino acids in the liver of rats fed a low protein diet might be one of the factors which cause the liver fat accumulation. To investigate the possibility were studied relationships between changes in concentrations of some metabolites of sulfur-containing amino acids and those in fat contents of rats fed a low protein diet consisting of heated soybean flour, casein or wheat flour with or without added methionine, threonine or lysine. The addition of 0.6% methionine to the 25% heated soybean flour diet increased the nonprotein-sulfhydryl (NP–SH) concentration and fat content in the liver. These changes were prevented by the further addition of 0.5% threonine to the diet, although the NP–SH concentration was remarkably higher than that of rats fed the unsupplemented diet. The addition of 0.6% cystine HC1 to the 25% heated soybean flour diet containing sufficient choline elevated the NP–SH concentration and fat content in the liver, which were not affected by the further addition of 0.5% threonine. The addition of 0.6% cystine HC1 to the 10% casein diet significantly increased the fat content, and NP–SH and taurine concentrations in the liver. The further addition of 0.5 % threonine completely decreased the fat content, and partially reduced the NP–SH and taurine concentrations. Effects of supplementation of 0.4% lysine HC1 to the 70% wheat flour diet on the fat content and NP–SH concentration in the liver demonstrated the trends similar to those of supplementation of cystine to the 10% casein diet. The further addition of threonine remarkably decreased the fat content, NP–SH and taurine concentrations in the liver.