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PubMed2002

An essential amino acid residue for catalytic activity of the dextranase of Streptococcus mutans.

Dextranase (Dex) is an enzyme that hydrolyzes glucan, a polymer of glucose synthesized from sucrose by glucosyltransferases (GTFs). By comparing amino acid sequences of Dexs and GTFs, we found that the Dex enzymes of Streptococcus mutans, Streptococcus sobrinus, Streptococcus downei and Streptococcus salivarius had similar amino acid sequences to those of the catalytic sites of GTFs of mutans streptococci. We therefore examined the amino acid essential in Dex catalysis by molecular genetic approaches in this study. Site-directed mutagenesis was used to convert the Asp-385 of the Dex molecule of S. mutans Ingbritt to Glu, Asn, Thr or Val. Replacement of Asp-385 with any of the amino acids resulted in complete disappearance of Dex activity. However, replacement of other Asp residues did not affect the enzyme activity. The inactive enzymes still retained dextran-binding ability. These results suggest that Asp-385 of the Dex of S. mutans Ingbritt was essential for enzyme activity and the catalytic and substrate-binding sites were located at different sites within the Dex molecule.

Amino Acid Sequence↗
PubMed2006

Increasing dietary crude protein does not increase the essential amino acid requirements of kittens.

Essential amino acid (EAA) requirements of omnivores and herbivores (e.g. chicks, lambs, pigs and rats) are directly related to the concentration of dietary crude protein (CP). When an EAA is limiting in the diet, addition of a mixture of EAA lacking the limiting one (which increases dietary CP) results in a decrease in food intake and weight gain. This interaction has been referred to as an AA imbalance and has not been studied in depth in strict carnivores. The objectives of these experiments were to examine the effects on growing kittens (2-week periods) of the addition to diets of a mixture of AA lacking the limiting one. The control diets were at the requirement of the respective limiting EAA (or about 85% of the 1986 National Research Council requirement). In experiment 1, with the dietary EAAs at the minimally determined requirements, the concentration of the essential or dispensable amino acids was increased to determine if CP or an EAA was limiting. Results of growth rates (n = 12) and plasma AA concentrations indicated that tryptophan was limiting, but increased body weight gain also occurred when the concentration of CP was increased as dispensable amino acids without additional tryptophan. Experiment 1 was repeated in experiment 2 using a crossover design. Again, when tryptophan was limiting additional concentrations of dispensable AAs increased body weight gain. This response is the opposite of that in herbivores and omnivores. Experiment 3 consisted of 10 separate crossover trials, one for each of the 10 EAA and examined the effect of two concentrations of dietary CP (200 and 300 g CP/kg diet) on body weight gain of kittens (n = 8) offered diets limiting in each respective EAA. Body weight gain was numerically greater when diets contained 300 g CP/kg than 200 g CP/kg for eight of 10 EAAs (p < 0.05 for only isoleucine and threonine) when each amino acid was limiting. This response is the reverse of that which occurs in chicks, lambs, pigs and rats when an EAA is limiting and dietary CP lacking the limiting EAA is increased. These results indicate that the EAA requirements of kittens are not positively correlated with dietary CP concentrations.

Amino Acids, Essential↗
PubMed1993

The plasma amino acid response to cafeteria feeding and essential-amino acid gavage in weaning rats.

The plasma amino acid concentrations of cafeteria-fed and standard-fed rats gavaged either an essential amino acid mixture or saline solution have been studied from 14 to 30 days after birth. The consumption of a cafeteria diet caused higher levels in many amino acids. The amino acid-gavaged cafeteria-fed rats showed the highest cysteine levels. The amino acid gavage produced lower concentrations of alanine, glutamate+glutamine, hydroxyproline, proline and ornithine, in both cafeteria-fed and standard-fed animals. The results show that the supply of amino acids has a positive effect on nitrogen retention and amino acid availability in cafeteria-fed pups.

Alanine↗
PubMed1996

Effect of glutamic acid on broilers given submarginal crude protein with adequate essential amino acids using feeds high and low in potassium.

Broiler males were examined for their response to feeds containing CP 1 to 2% below levels advocated by NRC (1994) and when supplemented with L-glutamic acid. Crude protein and glutamic acid treatments were imposed in starting, growing, and finishing feeds over 7 wk with K at high and low levels likely to occur in practice (0.80 vs 0.65 to 0.55%). All feeds were formulated to be isocaloric (3.20 kcal ME/g) and satisfy NRC (1994) essential amino acid (EAA) minimum requirements. Improved live weight gain occurred during the first 6 wk with supplementation of glutamic acid to the low CP feed but not when intact protein per se was used to increase CP. A similar advantage in growth was obtained from glutamic acid in response to its addition at equivalence of 1 to 2% CP as well as when dietary adjustments maintained low CP. Response to altered K could not be interpreted because of concurrent differences in glutamic acid and AMEn intakes. High glutamic acid levels did not decrease abdominal fat unless CP increased concurrently, whereas carcass back bruising and drumstick deformations were relieved by supplemental glutamic acid independent of CP. Increased weight gain from glutamic acid was only evident with drumsticks and debris that included the back when carcasses were cone-deboned. Supplemental glutamic acid is believed to improve the rate of connective tissue formation during rapid growth.

Amino Acids, Essential↗
PubMed1995

A di- and tripeptide transport system can supply Listeria monocytogenes Scott A with amino acids essential for growth.

Listeria monocytogenes takes up di- and tripeptides via a proton motive force-dependent carrier protein. This peptide transport system resembles the recently cloned and sequenced secondary di- and tripeptide transport system of Lactococcus lactis (A. Hagting, E. R. S. Kunji, K. J. Leenhouts, B. Poolman, and W. N. Konings, J. Biol. Chem. 269:11391-11399, 1994). The peptide permease of L. monocytogenes has a broad substrate specificity and allows transport of the nonpeptide substrate 5-aminolevulinic acid, the toxic di- and tripeptide analogs, alanyl-beta-chloroalanine and alanyl-alanyl-beta-chloroalanine, and various di- and tripeptides. No extracellular peptide hydrolysis was detected, indicating that peptides are hydrolyzed after being transported into the cell. Indeed, peptidase activities in response to various synthetic substrates were detected in cell extracts obtained from L. monocytogenes cells grown in brain heart infusion broth or defined medium. The di- and tripeptide permease can supply L. monocytogenes with essential amino acids for growth and might contribute to growth of this pathogen in various foods where peptides are supplied by proteolytic activity of other microorganisms present in these foods. Possible roles of this di- and tripeptide transport system in the osmoregulation and virulence of L. monocytogenes are discussed.

Amino Acids↗
PubMed1983

Bile acid and pancreatic trypsin outputs are parallel during intraduodenal infusion of essential amino acids.

There is disagreement as to whether contraction of the gallbladder occurs simultaneously with secretion of pancreatic enzymes during food ingestion. One study that employed exogenous cholecystokinin (CCK) alone showed dissociation of total bile acids (TBA) and trypsin outputs, while another study that employed exogenous CCK plus secretin showed parallel outputs of TBA and trypsin. Since previous studies have suggested that intraduodenal infusion of essential amino acids (EAA) evokes pancreaticobiliary secretion similar to that observed with food ingestion, we infused increasing doses of EAA intraduodenally in 10 subjects with intact gallbladder and in 10 subjects with previous cholecystectomy and measured total bile acids and trypsin outputs serially. In subjects with intact gallbladder, increasing molar doses of EAA induced parallel increases of TBA and trypsin outputs. In subjects with previous cholecystectomy trypsin outputs during infusion of EAA were similar to subjects with intact gallbladder, but their TBA outputs remained constant during the entire infusion period. Serial concentrations of plasma secretin did not change during intraduodenal infusion of EAA. These observations suggest that the gallbladder empties bile in concert with secretion of pancreatic enzymes following food ingestion.

Amino Acids, Essential↗
PubMed2001

Hepatic monitoring of essential amino acid availability may regulate IGF-I activity, thermogenesis, and fatty acid oxidation/synthesis.

Diets that are low in certain essential amino acids (EAAs), whether owing to low protein content or poor protein quality, tend to down-regulate systemic IGF-I activity, boost thermogenesis, and suppress hepatic capacity for lipogenesis, while promoting hepatic fatty acid oxidation. It is proposed that for each EAA there is a regulatory protein in hepatocytes whose activity is repressed by adequate levels of its EAA; if one (or more) of these regulatory proteins is active, it serves as a signal of EAA deficiency which then mediates the aforementioned effects on IGF-I activity, thermogenesis, and hepatic fatty acid metabolism. Mechanisms which monitor EAA availability likewise play a role in appetite regulation, thus accounting for the fact that spontaneous calorie consumption tends to be lower on high-protein diets. Diets low in protein quantity or quality may decrease insulin secretion, an effect which should contribute to their impact on IGF-I activity and lipid metabolism. The fact that vegans ingest diets that tend to be relatively low in certain EAAs may play a key role in their characteristic leanness and their decreased risk for diabetes, coronary disease, and cancer.

Amino Acids, Essential↗
PubMed1997

Identification of essential amino acids in phenylalanine ammonia-lyase by site-directed mutagenesis.

The postulated precursor of the prosthetic dehydroalanine of phenylalanine ammonia-lyase (PAL), serine 202, was changed to cysteine by site-directed mutagenesis. After cloning and heterologous expression in Escherichia coli, the gene product was assayed for PAL activity. Mutant S202C showed full catalytic activity, and its kinetic constants and the amount of thiol groups were identical to those of wild-type PAL. It must be concluded that in a posttranslational modification both water and hydrogen sulfide can be eliminated from the amino acid in position 202 to form dehydroalanine. In an attempt to identify further amino acids essential either for the posttranslational modification or for catalysis, arginine 174, glutamine 425, and lysine 499 were changed to isoleucine. Analysis of the heterologously expressed mutated gene products revealed that only the R174I mutant showed a significantly lower Vmax value (1/450) identifying this arginine as important. This finding was supported by treatment of wild-type PAL and mutant R174I with phenylglyoxal and 2,3-butandione. Both react specifically with the guanidino group of arginine. They irreversibly inhibited wild-type PAL but had no influence of the Vmax value of mutant R174I. Preincubation with l-phenylalanine protected wild-type PAL from inhibition by phenylglyoxal indicating that arginine 174 is close to the active site. Incubation with KCN irreversibly abolished the remaining activity of mutant R174I leading to the conclusion that arginine 174 is important in catalysis.

Amino Acids↗
PubMed1978

Intracellular free amino acids in muscle tissue of patients with chronic uraemia: effect of peritoneal dialysis and infusion of essential amino acids.

1. Free amino acids were determined in the plasma and in the muscle tissue of 14 patients with chronic uraemia; eight were not on dialysis and six were having regular peritoneal dialysis. The concentration of each amino acid in muscle water was calculated with the chloride method. 2. In both groups of patients there were low intracellular concentrations of threonine, valine, tyrosine and carnosine, and high glycine/valine and phenylalanine/tyrosine ratios. Both groups of patients had increased amounts of 1- and 3-methyl-histidine in plasma and in muscle water. 3. The non-dialysed patients had low intracellular concentrations of lysine, and the dialysed patients had high intracellular concentrations of lysine, isoleucine, leucine and of some of the non-essential amino acids. 4. After peritoneal dialysis for 22 h, the plasma concentration of several amino acids decreased but the intracellular concentrations of most amino acids did not change significantly. 5. Intravenous administration of essential amino acids and histidine during the last 4 h of dialysis increased in muscle the total free amino acids, the ratio of essential to non-essential amino acids and the valine and phenylalanine concentrations. 6. The results demonstrated that the plasma and muscle concentrations of several amino acids are grossly abnormal in chronic uraemia. Non-dialysed and dialysed patients exhibit important differences, especially in the intracellular amino acid patterns. Infusion of essential amino acids may result in enhancement of protein synthesis.

Amino Acids↗
PubMed1994

Essential amino acids and other essential components for development of Angiostrongylus costaricensis from third-stage larvae to young adults.

Third-stage larvae of Angiostrongylus costaricensis were cultured to the young adult stage in Waymouth's chemically defined medium MB 752/1, which contained 18 amino acids, 11 vitamins, glutathione, hypoxanthine, and glucose in a balanced salt solution. Nutritional requirements were examined by deletion of single components from Waymouth's medium. Ten amino acids, namely L-arginine, L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-threonine, L-tryptophan, and L-valine, were shown to be essential for the parasite's development. L-Aspartic acid, L-cysteine, L-cystine, L-glutamic acid, L-glutamine, glycine, L-proline, and L-tyrosine were not essential. Among the 11 vitamins, only choline chloride was essential for the development. The deletion of pyridoxine from the medium adversely affected parasite development. Glucose was also required by the worms, but glutathione and hypoxanthine were not required for their development. When the 10 essential L-amino acids were replaced individually by D-isomers of the same amino acids, none supported larval development in the manner of the L-amino acids.

Amino Acids, Essential↗
PubMed1984

Serum oxalic acid in uremia: effect of a low-protein diet supplemented with essential amino acids and ketoanalogues.

Serum oxalic acid (sOx) was determined with a new, specific enzymatic method in 73 uremic patients and the values were plotted against serum creatinine. 41 patients received a free mixed diet, and 32 similar patients were given a low-nitrogen diet supplemented with essential amino acids, ketoanalogues, and calcium carbonate (AD). A significant correlation was found between serum creatinine and sOx levels in patients following a free mixed diet, while no correlation appeared in patients on AD: The sOx concentrations were significantly lower and even normal in this group, and a significant reduction of sOx occurred in 10 patients with chronic renal failure, who changed from a free mixed diet to the AD. The lowering of sOx concentration in patients following AD is attributed both to low intake of its metabolic precursors and to the oral calcium carbonate supplementation.

Amino Acids, Essential↗
PubMed1998

A review of physiological and metabolic effects of essential amino acids.

The authors review ten essential amino acids with regard to their metabolic, physiologic and therapeutic effects throughout the human body. Physical properties of these biologically active compounds are discussed as a foundation for their diverse roles in special nitrogen containing products, neurotransmitters, and as alternative energy sources. Both normal and abnormal amino acid metabolism are considered in the areas of digestion, elimination of metabolic products, metabolic intermediates, and defects in these systems. Recent developments in therapeutic applications are further examined for clinical utility and as an economical alternative to traditional clinical treatment modalities.

Amino Acids, Essential↗
PubMed1982

A controlled study of supplementation with essential amino acids and alpha-keto acids in the conservative management of patients with chronic renal failure.

Oral therapy with essential amino acids (EAA) or alpha-keto acids (alpha-KA) has been recommended in patients with renal failure, but quality and quantity of optimal protein intake are still controversial. This study compares sequentially the effect of supplementation with EAA, and with alpha-KA versus placebo in 15 ambulatory patients with chronic renal failure (average creatinine clearance 10.8 ml/min), maintained on a protein diet of 0.57 g/kg body weight (40 g for a 70-kg patient). The actual dietary intake averaged 0.55 g protein/kg and 27 kcal/kg according to repeated 7-day dietary recordings. After a 6-week baseline period on this diet, all patients received additionally 0.112 g EAA/kg for 6 weeks followed by a double-blind crossover study of 0.105 g alpha-KA/kg versus placebo supplementation for 6 weeks each. Fasting blood samples for multiple parameters, including 15 indicators for protein deficiency, as well as anthropometric and clinical data were evaluated every 3 weeks. Laboratory data revealed no indications of protein deficiency. Therapy with alpha-KA diminished serum phosphate concentration (p less than 0.05), however no other significant beneficial effects could be demonstrated during supplementation with either EAA or alpha-KA. Therefore, such supplementation to a 0.55-g/kg-protein diet appears superfluous in stable ambulatory patients with renal insufficiency.

Adolescent↗
PubMed1984

Nitrogen balance studies in patients with uremia during treatment with protein-reduced diet and supplementation with essential amino acids or keto acids.

Nitrogen balance was studied in 4 patients with uremia during treatment with a protein-reduced diet (20 g) supplemented with either essential amino acids and histidine or a mixture of keto analogues of five of the essential amino acids and essential amino acids. 3 patients completed the study. Nitrogen balance was negative on the diet only and was improved with both forms of supplementation. However, supplementation with the keto acids did not offer any advantage over the conventional essential amino acid supplementation. 1 patient developed serious hypercalcemia during treatment with the keto acid supplementation.

Adult↗
PubMed1977

[Culex pipiens fatigans: labeling of tissues of normal and infected (Plasmodium cathemerium) females after feeding on tritiated amino acids (author's transl)].

Normal and infected Culex females were fed 11 different amino acids. These substances were labeled with tritium and each was given separately in glucose solution. After the uptake the marker appears first in crop, cardia and midgut. Later on the other tissues get labeled more or less. It seems that the labeling follows a characteristic pattern for each amino acid. Essential amino acids are taken up intensively; for example leucine not only in the midgut epithelium but also in the ovary and the fat body. There is nearly no uptake of the non-essential amino acids alanine, glutamic acid and DOPA by the tissues of both groups of females. These amino acids are only seen in the midgut area and not in the other tissues. In infected mosquitos the uptake of the essential acid, phenylalanine, corresponds only to that of a non-essential amino acid.

Amino Acids↗