Efficiency of alpha-ketoisocaproic acid as a substitute for leucine in the diet of the growing rat.
(25/363)
Immature male albino rats (70-80 g), eating a diet furnishing all nutrients for optimal growth and containing 84.6 mumoles of leucine/g, gained weight at an average rate of 5.9 g/day. Removal of leucine caused an average daily weight loss of 1.3 g. Addition of leucine to the diet in graduated amounts corrected this weight loss, the improvement in body weight (BW) being proportional to the dietary content of leucine. Addition of alpha-ketoisocaproic acid in place of leucine to the leucine-free diet also prevented loss of BW. Percentage efficiency of alpha-ketoisocaproic acid as a dietary substitute for leucine was calculated as: (see article). Efficiency of such substitution varied from 27% for a diet containing 84.6 mumoles of alpha-ketoisocaproic acid/g to 20% for a diet containing 169.2 alpha-ketoisocaproic acid/g. (+info)
Essential dietary amino acids for growth of larvae of the yellow mealworm, Tenebrio molitor L.
(26/363)
Larvae of the yellow mealworm, Tenebrio molitor L., have been used to evaluate nutritional quality of proteins and protein isolates. However, such investigations have been complicated by lack of knowledge of dietary requirements of the larvae. To determine essential dietary amino acids for growth of Tenebrio molitor, single amino acids were deleted from the amino acid mixture of the diet. Diets were maintained isonitrogenous with supplementary glycine and, in the case of deleted glycine, with glutamic acid. Growth, as measured by gain in weight, and survival were observed over a 4-week period at 27 plus or minus 0.25 degrees and 65 plus or minus 5% relative humidity. The results indicate that larvae of Tenebrio molitor require a dietary source of the same 10 amino acids essential for growth in rats, other vertebrates, and some protozoa. They also showed that serine, tyrosine, glutamic acid, and possibly glycine were dispensable for growth in this insect. Alanine, cystine, proline, and aspartic acid appeared semidispensable. Survival over the 4-week experimental period was unaffected by deleting amino acids from the diet. The results are discussed in relation to amino acid requirements of other insects and to suggested improvement of the diet of the present investigation. (+info)
Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise.
(27/363)
The present study was designed to determine whether consumption of an oral essential amino acid-carbohydrate supplement (EAC) before exercise results in a greater anabolic response than supplementation after resistance exercise. Six healthy human subjects participated in two trials in random order, PRE (EAC consumed immediately before exercise), and POST (EAC consumed immediately after exercise). A primed, continuous infusion of L-[ring-(2)H(5)]phenylalanine, femoral arteriovenous catheterization, and muscle biopsies from the vastus lateralis were used to determine phenylalanine concentrations, enrichments, and net uptake across the leg. Blood and muscle phenylalanine concentrations were increased by approximately 130% after drink consumption in both trials. Amino acid delivery to the leg was increased during exercise and remained elevated for the 2 h after exercise in both trials. Delivery of amino acids (amino acid concentration times blood flow) was significantly greater in PRE than in POST during the exercise bout and in the 1st h after exercise (P < 0.05). Total net phenylalanine uptake across the leg was greater (P = 0.0002) during PRE (209 +/- 42 mg) than during POST (81 +/- 19). Phenylalanine disappearance rate, an indicator of muscle protein synthesis from blood amino acids, increased after EAC consumption in both trials. These results indicate that the response of net muscle protein synthesis to consumption of an EAC solution immediately before resistance exercise is greater than that when the solution is consumed after exercise, primarily because of an increase in muscle protein synthesis as a result of increased delivery of amino acids to the leg. (+info)
Deficiency of dietary EAA preferentially inhibits mRNA translation of ribosomal proteins in liver of meal-fed rats.
(28/363)
The goal of these studies was to investigate the mechanisms by which amino acid supply regulates global rates of protein synthesis as well as the translation of ribosomal protein (rp) mRNAs in liver. In the experiments conducted, male weanling rats were trained over a 2-wk period to consume their daily food intake within 3 h. On day 14, rats were fed the control diet or an isocaloric, isonitrogenous diet lacking glycine, tryptophan, leucine, or the branched-chain amino acids (BCAA) for 1 h. Feeding Trp-, Leu-, or BCAA-deficient diets resulted in significant reductions in serum insulin, hepatic protein synthesis, eukaryotic initiation factor 2B (eIF2B) activity, and phosphorylation of eIF4E-binding protein 1 (4E-BP1) and ribosomal protein S6 kinase (S6K1). Phosphorylation of eIF2alpha was inversely related to eIF2B activity under all conditions. Alterations in the hepatic synthesis of rp were assessed by changes in the distribution of rp (S4, S8, L26) mRNAs across sucrose density gradients and compared with non-rp (beta-actin, albumin) mRNAs. In all dietary treatments, non-rp mRNAs were mostly polysome associated. Conversely, the proportion of rp mRNAs residing in polysomes was two- to fivefold less in rats fed diets lacking tryptophan, leucine, or BCAA compared with rats fed the control diet. Total hepatic abundance of all mRNAs examined did not differ among treatment groups. For all parameters examined, there were no differences between rats fed the glycine-deficient diet and rats fed the control diet. The data suggest that essential amino acid (EAA) deficiency inhibits global rates of liver protein synthesis via a block in translation initiation. Additionally, the translation of rp mRNAs is preferentially repressed in association with decreased S6K1 phosphorylation. (+info)
Amino acid regulation of gene expression.
(29/363)
Regulation of gene expression by amino acids is mediated through a number of mechanisms affecting both the transcription of DNA and the translation of mRNA. This report reviews recent findings demonstrating a role for amino acids in regulating the initiation phase of mRNA translation. The report focuses on key regulatory events in translation initiation and discusses some of the signaling pathways through which amino acid sufficiency or the lack thereof is communicated within the cell. It concludes with a consideration of some of the important unanswered questions in this rapidly advancing area of research. (+info)
Human L-type amino acid transporter 1 (LAT1): characterization of function and expression in tumor cell lines.
(30/363)
System L is a major nutrient transport system responsible for the transport of large neutral amino acids including several essential amino acids. We previously identified a transporter (L-type amino acid transporter 1: LAT1) subserving system L in C6 rat glioma cells and demonstrated that LAT1 requires 4F2 heavy chain (4F2hc) for its functional expression. Since its oncofetal expression was suggested in the rat liver, it has been proposed that LAT1 plays a critical role in cell growth and proliferation. In the present study, we have examined the function of human LAT1 (hLAT1) and its expression in human tissues and tumor cell lines. When expressed in Xenopus oocytes with human 4F2hc (h4F2hc), hLAT1 transports large neutral amino acids with high affinity (K(m)= approximately 15- approximately 50 microM) and L-glutamine and L-asparagine with low affinity (K(m)= approximately 1.5- approximately 2 mM). hLAT1 also transports D-amino acids such as D-leucine and D-phenylalanine. In addition, we show that hLAT1 accepts an amino acid-related anti-cancer agent melphalan. When loaded intracellularly, L-leucine and L-glutamine but not L-alanine are effluxed by extracellular substrates, confirming that hLAT1 mediates an amino acid exchange. hLAT1 mRNA is highly expressed in the human fetal liver, bone marrow, placenta, testis and brain. We have found that, while all the tumor cell lines examined express hLAT1 messages, the expression of h4F2hc is varied particularly in leukemia cell lines. In Western blot analysis, hLAT1 and h4F2hc have been confirmed to be linked to each other via a disulfide bond in T24 human bladder carcinoma cells. Finally, in in vitro translation, we show that hLAT1 is not a glycosylated protein even though an N-glycosylation site has been predicted in its extracellular loop, consistent with the property of the classical 4F2 light chain. The properties of the hLAT1/h4F2hc complex would support the roles of this transporter in providing cells with essential amino acids for cell growth and cellular responses, and in distributing amino acid-related compounds. (+info)
Dynamic ideal protein and limiting amino acids for lactating sows: the impact of amino acid mobilization.
(31/363)
The limiting amino acids for lactating sows were determined using 28 primiparous sows that were intentionally underfed both energy and protein during a 21-d lactation. Groups of four sows were allotted to litter-size treatments of 6, 7, 8, 9, 10, 11, or 12 by cross-fostering as needed within 48 h postpartum. Sows were killed on d 21 of lactation. The carcass, liver, gastrointestinal tract, reproductive tract, mammary gland, and other viscera were separated, weighed, ground, and analyzed for dry matter, crude protein, and amino acids. Simple linear equations were obtained for each amino acid within tissues as a function of litter size. The mobilization of amino acids from carcass, liver, gastrointestinal tract, reproductive tract, and other viscera increased as litter size increased. Amino acids were accreted to mammary glands as litter size increased (2.65 g lysine/21 d for each one-pig increase in litter size). Milk production needs were estimated (49.9 g lysine/21 d for each one-pig increase in litter size). The quantity of each amino acid required additionally as litter size increased was obtained from the difference between amino acid needs for milk production and mammary gland growth and those provided from tissue mobilization. The relative ratio among amino acids that are required additionally (ideal amino acid pattern) was compared with the relative ratio of amino acids that can be provided from a corn-soybean meal lactation diet. From the comparison, it was shown that threonine and lysine are the first-limiting amino acids, followed by valine, when tissue mobilization occurs during lactation. Lysine is the first-limiting amino acid, and valine becomes second-limiting followed by threonine, when sows do not mobilize body tissues during lactation. Thus, the limiting order of essential amino acids changes depending on feed intake and tissue mobilization of sows during lactation. Proper feeding of lactating sows should consider the expected degree of tissue mobilization during lactation. (+info)
Free amino acid levels in the blood of patients undergoing parenteral alimentation.
(32/363)
Free amino acid levels were determined in the blood of patients undergoing parenteral alimentation. During amino acid infusions, alanine, valine, glycine, isoleucine, leucine, proline, threonine, serine, methionine, phenylalanine, and lysine levels increased. Bivariate regression analysis was then done to determine the average rise in each amino acid when 1 mmole/hr of that amino acid was infused and when 1 mmole/hr of glucose was infused. This analysis was done on both arterial plasma and arterial wh-le blood increments. The average rise in the amino acid level with 1 mmole of infusion per hour varied from 32 to 133 mumole/liter. Only alanine levels were positively correlated with glucose infusion, while the branched chain levels were all negatively correlated. In no instance could a significant positive arteriovenous difference across the forearm be correlated with the infusion of an amino acid, despite amino acid levels as much as five times normal. Methionine, proline, valine, threonine, and lysine showed the greatest rise in blood concentration per millimole of amino acid infused per hour suggesting that their degradation or use in protein synthesis was limited. While the blood concentration rise in glycine was only about half as much per millimole per hour infused as was found in the previously mentioned group of amino acids, high rates of infusion of this amino acid resulted in large increments inglycine levels. It may be desirable to reduce the amounts of these amino acids in parenteral amino acid formulations. (+info)