Urea, citrate and orotate excretion in growing rats fed amino acid-deficient diets.
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Male, weanling rats were fed a control purified amino acid diet or the same diet with lysine, phenylalanine, tryptophan, valine, or arginine omitted singly, or both arginine and lysine omitted. Blood urea reached three to four times that of control levels with all deficient diets. Urea excretion increased almost linearly with time during the first 3 days of amino acid deficiency. Rates of urea excretion on day 3 in decreasing order for various deficiencies were as follows: lysine and arginine combined are more than lysine is more than tryptophan equals valine is more that phenylalanine equals arginine. Urinary citrate was 26 and 21.8 times that of control values without arginine and 11.4 and 6.2 times that of control values without lysine on days 2 and 3, respectively. By day 8 citrate excretion had returned to control levels without lysine but not without arginine. Citrate excretion was unchanged with other deficiencies. Orotic acid excretion increased markedly only without arginine and slightly without tryptopahn. A deficiency of arginine and lysine increased urea and citrate excretions to a greater extent than either deficiency alone. Two injections of arginine or homoarginine (0.50 mmole/injection) given at 12-hour intervals to rats fed no lysine and arginine for 3 days decreased citrate excretion immediatedly and on the following day. Urea excretion decreased with injected homoarginine, but not with arginine. Orotic acid excretion increased more than four times on the day of homoarginine injection compared with that of the preceding day. Arginine injection returned orotic acid excretion to nearly control levels within 24 hours. Urea degradation in the gastrointestinal tract was increased in animals fed amino acid-deficient diets. (+info)
Use of a whey protein concentrate as a supplement to maize, rice and potatoes: a chemical and biological evaluation using growing rats.
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Liquid whey has long been known to contain proteins of high nutritional value, but their use in human nutrition has been complicated by the high lactose and low protein contents of the whey. Modern technological processes of gel filtration and ultrafiltration have made possible the production of whey protein concentrates (WPC) low in lactose. In this investigation, the supplementary effect of WPC on maize and rice proteins was compared with the corresponding effect of dried skim milk (DSM). Protein quality was studied by chemical and biological methods on growing rats. Biological tests performed on both raw and boiled protein mixtures showed WPC to be superior to DSM in supplementing maize and rice proteins. The nutritive value of a potato-WPC mixture was also studied and compared with those of potato-lactalbumin and potato-egg mixtures, both of which are known to contain protein of very high quality for man. The comparison indicated that a potato-WPC mixture may also possess high protein quality. (+info)
Quantifying nutrient production by the microbial symbionts in an aphid.
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The symbiotic bacteria Buchnera sp. provide aphids with essential amino acids, nutrients in short supply in the aphid diet of plant phloem sap. The contribution of Buchnera-derived amino acids to net protein growth of the aphid Aphis fabae was quantified from the protein growth of aphids reared on chemically defined diets lacking individual amino acids. The amino acid production rates varied among the nine essential amino acids over the range 8-156 pmol microg(-1)protein day(-1) (for tryptophan and leucine, respectively), equivalent to 0.02-0.33 fmol Buchnera(-1)day(-1). In a complementary metabolic analysis, the aphids incorporated radioactivity from dietary [(14)C]glutamic acid into the essential amino acids isoleucine, lysine and threonine. Incorporation into isoleucine was significantly elevated by the omission of dietary isoleucine, indicating that dietary supply may affect the biosynthetic rates of certain amino acids by Buchnera. Aphids experimentally deprived of Buchnera did not synthesize essential amino acids from dietary glutamic acid. The mortality of aposymbionts was high over 7 days on the phenylalanine-free diet, and their assimilation of dietary leucine was depressed on the complete diet, suggesting that both the absence of bacteria-derived amino acids and the low rates of assimilation of certain dietary amino acids may contribute to the poor growth of these insects. (+info)
Effect of different levels of gossypol on transaminase activity, on nonessential to essential amino acid ratio, and on iron and nitrogen retention in rats.
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Metabolic experiments with rats fed rations containing varying levels of free gossypol (from 3 to 109 mg/100 g) showed that nitrogen retention was not affected by gossypol while iron absorption decreased as the levels of gossypol in the ration increased. This in turn resulted in lower hematocrit and hemoglobin values and lower levels of iron in the liver. The levels of glutamic-oxaloacetic and glutamic-pyruvic transaminases, an indication of liver necrosis, increased in blood serum and decreased in liver when gossypol was fed. The ratio of nonessential to essential amino acids in both serum and liver increased with increasing levels of gossypol in the diet showing that, in spite of an equalized available lysine intake, the cottonseed pigment was capable of binding this and/or other essential amino acids. In all cases, weight gain was adversely affected by the level of gossypol used. (+info)
Nitrogen retention and plasma amino acids of men who consumed isonitrogenous diets containing egg albumen or mixtures of amino acids.
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Experimental diets that furnished approximately 6.0 g of nitrogen per day were consumed by young men. Nitrogen retention was not altered significantly when egg albumen was replaced by its constituent essential and nonessential amino acids or by the essential amino acids (including cystine, tyrosine and histidine) plus a source of nonspecific nitrogen. Concentrations of essential amino acids in fasting or postprandial plasma were not influenced significantly by source of amino acids or by replacement of nonessential amino acids by nonspecific nitrogen; but concentrations of certain nonessential amino acids were altered by treatment. Responses to an elemental diet or to a similar diet in which egg albumen replaced the amino acid mixture did not differ significantly. (+info)
Is glucose/amino acid supplementation after exercise an aid to strength training?
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BACKGROUND: The precise timing of carbohydrate and amino acid ingestion relative to a bout of resistance exercise may modulate the training effect of the resistance exercise. OBJECTIVE: To assess whether regular glucose/amino acid supplementation immediately after resistance exercise could enhance the gain in muscle strength brought about by resistance training. METHODS: Seven untrained participants with a median age of 23 years and mean (SD) body mass 68.9 (13.5) kg resistance trained on a leg extension machine for five days a week for 10 weeks, using four sets of 10 repetitions. Alternate legs were trained on successive days, one leg each day. Subjects ingested either a supplement including 0.8 g glucose/kg and 0.2 g amino acids/kg, or placebo, on alternate training days immediately after training. Therefore the supplement was always ingested after training the same leg (supplement leg). Isometric, isokinetic, and 1 repetition maximum (RM) strength were measured before, during, and after training. Blood samples were analysed to determine the acute responses of insulin and glucose to resistance exercise and supplementation or placebo. RESULTS: Serum insulin concentration peaked 20 minutes after supplement ingestion at ninefold the placebo level, and remained significantly elevated for at least 80 minutes (p<0.01). Isometric, isokinetic, and 1 RM strength improved on both supplement and placebo legs (p<0.05). There were no significant differences in the gain in strength between the supplement leg and the placebo leg (p>0.05). CONCLUSION: Regular glucose/amino acid supplementation immediately after resistance exercise is unlikely to enhance the gain in muscle strength brought about by resistance training. (+info)
Essential amino acids of Escherichia coli DnaC protein in an N-terminal domain interact with DnaB helicase.
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Escherichia coli DnaC protein bound to ATP forms a complex with DnaB protein. To identify the domain of DnaC that interacts with DnaB, a genetic selection was used based on the lethal effect of induced dnaC expression and a model that inviability arises by the binding of DnaC to DnaB to inhibit replication fork movement. The analysis of dnaC alleles that preserved viability under elevated expression revealed an N-terminal domain of DnaC involved in binding to DnaB. Mutant proteins bearing single amino acid substitutions (R10P, L11Q, L29Q, S41P, W32G, and L44P) that reside in regions of predicted secondary structure were inert in DNA replication activity because of their inability to bind to DnaB, but they retained ATP binding activity, as indicated by UV cross-linking to [alpha-(32)P]ATP. These alleles also failed to complement a dnaC28 mutant. Other selected mutations that map to regions carrying Walker A and B boxes are expected to be defective in ATP binding, a required step in DnaB-DnaC complex formation. Lastly, we found that the sixth codon from the N terminus encodes aspartate, resolving a reported discrepancy between the predicted amino acid sequence based on DNA sequencing data and the results from N-terminal amino acid sequencing (Nakayama, N., Bond, M. W., Miyajima, A., Kobori, J., and Arai, K. (1987) J. Biol. Chem. 262, 10475-10480). (+info)
Determination of essential amino acids involved in the CD4-independent tropism of the X4 human immunodeficiency virus type 1 m7NDK isolate: role of potential N glycosylations in the C2 and V3 regions of gp120.
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Seven mutations in the C2, V3, and C3 regions of gp120 are implicated in the tropism of the first CD4-independent human immunodeficiency virus type 1 isolate, m7NDK. Site-directed mutagenesis revealed that three amino acids are essential to maintain this tropism, one in the C2 region and two in the V3 loop. Two mutations implied N glycosylation modifications. (+info)