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.     

In Vitro Stimulation by Parathion of Porcine Pancreatic Carboxylesterase Activity toward Triacetin

In order to elucidate the relationship between bitter taste and chemical structure in peptides, various kinds of model bitter peptides containing arginine, proline and phenylalanine were synthesized, and the contribution of the individual amino acids to the bitter taste was made clear. It was confirmed that, in order to strengthen the bitterness in di- and tripeptides, the hydrophobic amino acid needs to be located at the C-terminal and, conversely, the basic amino acid should be located at the N-terminal Furthermore, a strong bitter taste was observed when arginine was contiguous to proline such as Arg-Pro, Gly-Arg-Pro and Arg-Pro-Gly. A synergistic effect for bitter taste was observed in the peptides whose structure is (Arg)_l-(Pro)_m-(Phe)_n (l=1, 2; m, n = 1 ~ 3) by increasing the number of amino acids. Among them, the octapeptide (Arg-Arg-Pro-Pro-Pro-Phe-Phe-Phe) possessed an extremely bitter taste with its threshold value of 0.002 mm and was found to be the most bitter among the peptides.     

Behavioural and metabolic responses of the Antarctic sea star Odontaster validus to food stimuli of different concentration

Experiments were carried out to study the behavioural and metabolic responses of the Antarctic sea star, Odontaster validus, to different concentration of food signals (glutamic acid, aspartic acid, glicyne, alanine, tyrosine and a mixture of 11 amino acids). Stimulus concentration increase caused a rise in both the percentage of reacting animals and in the reaction intensity. At low stimulus concentration, O. validus reaction consisted of tube foot waving, and only high concentrations elicited a complicated sequence of several types of behaviour. The metabolic rate of small O. validus was more sensitive to chemical stimuli than of large individuals, with small sea stars reacting even to low signal concentration. It can be speculated that small body size can be a factor restricting sea star capabilities and influencing its reaction to chemical signals.     

Dietary fatty acids promote sleep through a taste‐independent mechanism

Consumption of foods that are high in fat contribute to obesity and metabolism‐related disorders. Dietary lipids are comprised of triglycerides and fatty acids, and the highly palatable taste of dietary fatty acids promotes food consumption, activates reward centers in mammals and underlies hedonic feeding. Despite the central role of dietary fats in the regulation of food intake and the etiology of metabolic diseases, little is known about how fat consumption regulates sleep. The fruit fly, Drosophila melanogaster, provides a powerful model system for the study of sleep and metabolic traits, and flies potently regulate sleep in accordance with food availability. To investigate the effects of dietary fats on sleep regulation, we have supplemented fatty acids into the diet of Drosophila and measured their effects on sleep and activity. We found that flies fed a diet of hexanoic acid, a medium‐chain fatty acid that is a by‐product of yeast fermentation, slept more than flies starved on an agar diet. To assess whether dietary fatty acids regulate sleep through the taste system, we assessed sleep in flies with a mutation in the hexanoic acid receptor Ionotropic receptor 56D, which is required for fatty acid taste perception. We found that these flies also sleep more than agar‐fed flies when fed a hexanoic acid diet, suggesting the sleep promoting effect of hexanoic acid is not dependent on sensory perception. Taken together, these findings provide a platform to investigate the molecular and neural basis for fatty acid‐dependent modulation of sleep.     

Injection of essential amino acids substitutes for bacterial supply in aposymbiotic pea aphids (Acyrthosiphon pisum)

The symbiotic bacteria Buchnera contribute to the nutrition of pea aphids, Acyrthosiphon pisum, through the provision of essential amino acids which are lacking in the diet. However, chemically defined diets, containing nutritionally adequate amounts of essential amino acids, fail to rescue aposymbiotic aphids, in which the bacteria have been disrupted with antibiotics. In this study the injection of a mixture of essential amino acids into the haemocoel of aposymbiotic aphids was shown to alleviate, at least partially, the impact of symbiont loss. Specifically, the total amino acid content in the tissues of aposymbiotic aphids was reduced by approximately 40% to levels comparable with symbiotic insects, and there was a 1.7-fold increase in the number of embryos, suggesting that the availability of essential amino acids promotes aphid protein synthesis by rejuvenating the free amino acid pool of aposymbiotic aphids. In addition, a similar effect on the total amino acid content was observed when phenylalanine alone, but not glutamine, lysine or tryptophan, was injected into the haemocoel of aposymbiotic aphids, and there was also a significant increase in the number of embryos following injection of phenylalanine or tryptophan alone. The impact of amino acid injection on the embryo complement of aposymbiotic aphids was limited to an increase in the number of embryos, with no increase in basal embryo size. It is proposed that older embryos may rely on their own complement of symbiotic bacteria for essential amino acid provisioning. Taken together, the data highlight the importance of bacterial provisioning of essential amino acids, particularly the aromatic amino acids, in the intact symbiosis.     

Linoleic and oleic acids alter the licking responses to sweet, salt, sour, and bitter tastants in rats

The free fatty acids (FFAs), linoleic and oleic acids, commonly found in dietary fats can be detected by rats on the basis of gustatory cues following conditioned taste aversion pairings. FFAs depolarize the membrane potential of isolated rat taste receptor cells by inhibiting delayed rectifying potassium channels. This study examined the licking response of rats to sweet, salt, sour, and bitter taste solutions when 88 muM linoleic acid, 88 muM oleic acid, or an 88 muM linoleic-oleic acid mixture was added to the solutions. The presence of linoleic, oleic, and the linoleic-oleic acid mixture in sweet solutions produced increases in the licking responses, whereas adding linoleic, oleic, and the linoleic-oleic acid mixture to salt, sour, or bitter taste solutions produced decreases in licking responses when compared with the licking responses to the solutions in the absence of the FFAs. We conclude that FFAs may act in the oral cavity to depolarize taste receptor cells and therefore to increase the perceived intensity of concomitant tastants, thus contributing to the enhanced palatability associated with foods containing high dietary fat.     

Electro-olfactogram and multiunit olfactory receptor responses to complex mixtures of amino acids in the channel catfish, Ictalurus punctatus

In vivo electrophysiological recordings from populations of olfactory receptor neurons in the channel catfish, Ictalurus punctatus, clearly showed that both electro-olfactogram and integrated neural responses of olfactory receptor cells to complex mixtures consisting of up to 10 different amino acids were predictable with knowledge of (a) the responses to the individual components in the mixture and (b) the relative independence of the respective receptor sites for the component stimuli. All amino acid stimuli used to form the various mixtures were initially adjusted in concentration to provide approximately equal response magnitudes. Olfactory receptor responses to both multimixtures and binary mixtures were recorded. Multimixtures were formed by mixing equal aliquots of 3-10 different amino acids. Binary mixtures were formed by mixing equal aliquots of two equally stimulatory solutions. Solution 1 contained either one to nine different neutral amino acids with long side-chains (LCNs) or one to five different neutral amino acids with short side-chains (SCNs). Solution 2, comprising the binary mixture, consisted of only a single stimulus, either a LCN, SCN, basic, or acidic amino acid. The increasing magnitude of the olfactory receptor responses to mixtures consisting of an increasing number of neutral amino acids indicated that multiple receptor site types with highly overlapping specificities exist to these compounds. For both binary mixtures and multimixtures composed of neutral and basic or neutral and acidic amino acids, the receptor responses were significantly enhanced compared with those mixtures consisting of an equal number of only neutral amino acids. These results demonstrate that receptor sites for the basic and acidic amino acids, respectively, are highly independent of those for the neutral amino acids, and suggest that a mechanism for synergism is the simultaneous activation of relatively independent receptor sites by the components in the mixture. In contrast, there was no evidence for the occurrence of mixture suppression.     

Regulation of RNA degradation in cultured rat hepatocytes: Effects of specific amino acids and insulin

The regulation of RNA degradation by specific amino acids and insulin was investigated in cultured rat hepatocytes from fed rats previously injected in vivo with [6-¹⁴C]orotic acid. The effects of three groups of amino acids were compared to those of a complete amino acid mixture. The first one consisted of the eight amino acids (leucine, proline, glutamine, histidine, phenylalanine, tyrosine, methionine, tryptophan) previously found to be particularly effective in the control of proteolysis. The two other groups were defined from our study with single additions of amino acids, one consisting of proline, asparagine, glutamine, alanine, phenylalanine, and leucine and the other including the latter group with serine, histidine, and tyrosine. The results showed that these three groups were able to strongly inhibit deprivation-induced RNA breakdown at one and ten times normal plasma concentrations but to a lower extent than the complete amino acid mixture. Six amino acids (proline, asparagine, glutamine, alanine, phenylalanine, leucine) inhibited individually RNA degradation by more than 20%. However, the deletions of proline, asparagine, glutamine, or alanine from the group of these six amino acids were not followed by a loss of inhibitory effect. On the contrary, an important loss of inhibition was observed when leucine and phenylalanine were deleted. Furthermore, only these two amino acids exhibited an additive inhibitory effect. Thus leucine and phenylalanine could be considered as important inhibitors of RNA breakdown in cultured rat hepatocytes. Finally, insulin which had no significant effect on RNA degradation in the absence of amino acids, was able to potentiate the inhibitory effect of different amino acid groups. © 1993 Wiley-Liss, Inc.     

Taste Responses to Binary Mixtures of Amino Acids in the sea catfish, Arius felis

In vivo electrophysiological recordings in the sea catfish,Arius felis, showed that the magnitude of the integrated facialtaste responses to binary mixtures of amino acids was predictablewith knowledge obtained from previous cross-adaptation studiesof the relative independence of the respective binding sitesof the component stimuli. Each component from which equal aliquotswere drawn to form the mixtures was adjusted in concentrationto provide for approximately equal reponse magnitudes. The magnitudeof the taste responses to binary mixtures whose component aminoacids showed minimal cross-adaptation was significantly greaterthan that to binary mixtures whose components exhibited considerablecross-reactivity. There was no evidence for mixture suppression.The relative magnitude of the taste responses in the sea catfishto stimulus mixtures is similar to that previously reportedfor olfactory receptor responses in the freshwater channel catfishand chorda tympani taste responses in the hamster. Chem. Senses21: 45–53, 1996.     

Specificity of Amino Acid Transport in Trypanosoma equiperdum*

Uptake of [¹⁴C] alanine, arginine, glutamic acid and phenylalanine by Trypanosoma equiperdum occurred by both a mediated mechanism and diffusion. Twenty amino acids were studied as inhibitors of absorption of the above amino acids. Results suggested that at least 4 distinct transport loci are involved in amino acid transport. These 4 loci have overlapping affinities for amino acids and seem to be involved, respectively, in the absorption of (a) arginine and phenylalanine; (b) arginine; (c) alanine, phenylalanine, and glutamic acid; (d) glutamic acid. The data also showed that multiple sites for substrate binding occur on each of 2 transport systems.     

Allelic variation of the Tas1r3 taste receptor gene selectively affects taste responses to sweeteners: evidence from 129.B6-Tas1r3 congenic mice.

The Tas1r3 gene encodes the T1R3 receptor protein, which is involved in sweet taste transduction. To characterize ligand specificity of the T1R3 receptor and the genetic architecture of sweet taste responsiveness, we analyzed taste responses of 129.B6-Tas1r3 congenic mice to a variety of chemically diverse sweeteners and glucose polymers with three different measures: consumption in 48-h two-bottle preference tests, initial licking responses, and responses of the chorda tympani nerve. The results were generally consistent across the three measures. Allelic variation of the Tas1r3 gene influenced taste responsiveness to nonnutritive sweeteners (saccharin, acesulfame-K, sucralose, SC-45647), sugars (sucrose, maltose, glucose, fructose), sugar alcohols (erythritol, sorbitol), and some amino acids (D-tryptophan, D-phenylalanine, L-proline). Tas1r3 genotype did not affect taste responses to several sweet-tasting amino acids (L-glutamine, L-threonine, L-alanine, glycine), glucose polymers (Polycose, maltooligosaccharide), and nonsweet NaCl, HCl, quinine, monosodium glutamate, and inosine 5'-monophosphate. Thus Tas1r3 polymorphisms affect taste responses to many nutritive and nonnutritive sweeteners (all of which must interact with a taste receptor involving T1R3), but not to all carbohydrates and amino acids. In addition, we found that the genetic architecture of sweet taste responsiveness changes depending on the measure of taste response and the intensity of the sweet taste stimulus. Variation in the T1R3 receptor influenced peripheral taste responsiveness over a wide range of sweetener concentrations, but behavioral responses to higher concentrations of some sweeteners increasingly depended on mechanisms that could override input from the peripheral taste system.     

THE EFFECTS OF PHENYLALANINE ON AMINO ACID METABOLISM AND PROTEIN SYNTHESIS IN BRAIN CELLS IN VITRO1

Incubation of brain cell suspensions with 14 mM-phenylalanine resulted in rapid alterations of amino acid metabolism and protein synthesis. Both thc rate of uptake and the final intracellular concentration of several radioactively-labelled amino acids were decreased by high concentrations oi phenylalanine. By prelabelling cells with radioactive amino acids, phenylalanine was also shown to effect a rapid loss of the labelled amino acids from brain cells. Amino acid analysis after the incubation of the cells with phenylalanine indicated that several amino acids were decreased in their intracellular concentrations with effects similar to those measured with radioisotopic experiments (large neutral > small and large basic > small neutral > acidic amino acids). Although amino acid uptake and efflux were altered by the presence of 14 mwphenylalanine, little or no alteration was detected in the resulting specific activity of the intracellular amino acids. High levels of phenylalanine did not significantly altcr cellular catabolism of either alanine, lysine, leucine or isoleucine. As determined by the isolation of labcllcd aminoacyl-tRNA from cells incubated with and without phenylalanine, there was little or no alteration in the level of this precursor for radioactive alanine and lysine. There was, however, a detectable decrease in thc labelling of aminoacyl-tRNA for leucine and isoleucine. Only aftcr correcting for the changes of the specific activity of the precursors and thcir availability to translational events, could the effects of phenylalanine on protein synthesis be established. An inhibition of the incorporation into protein for each amino acid was approximately 20%.     

Gustatory sensation of l- and d-amino acids in humans

Amino acids are known to elicit complex taste, but most human psychophysical studies on the taste of amino acids have focused on a single basic taste, such as umami (savory) taste, sweetness, or bitterness. In this study, we addressed the potential relationship between the structure and the taste properties of amino acids by measuring the human gustatory intensity and quality in response to aqueous solutions of proteogenic amino acids in comparison to d-enantiomers. Trained subjects tasted aqueous solution of each amino acid and evaluated the intensities of total taste and each basic taste using a category-ratio scale. Each basic taste of amino acids showed the dependency on its hydrophobicity, size, charge, functional groups on the side chain, and chirality of the alpha carbon. In addition, the overall taste of amino acid was found to be the combination of basic tastes according to the partial structure. For example, hydrophilic non-charged middle-sized amino acids elicited sweetness, and l-enantiomeric hydrophilic middle-sized structure was necessary for umami taste. For example, l-serine had mainly sweet and minor umami taste, and d-serine was sweet. We further applied Stevens’ psychophysical function to relate the total-taste intensity and the concentration, and found that the slope values depended on the major quality of taste (e.g., bitter large, sour small).     

Taste effects of some amino acids and glutamate compounds in the rat

Behavioral responses to five L-amino acids (Gly, Arg, Leu, Ala,Met) and five related L-glutamate compounds (MSG, MKG, MAG,Gln, GluHCl) were measured using 1-min taste reactivity andstandard 24-h, two-bottle preference tests. Taste reactivitytests measure the immediate pattern of ingestive and aversiveoral motor behavior elicited by direct oral infusion of tastestimuli. By permitting acute observations in non-deprived rats,taste reactivity tests are more sensitive to taste factors thanstandard long-term tests. Three stimulus concentrations of eachcompound were selected by behavioral and electrophysiologicalcriteria. Taste reactivity results often conflicted with standardintake results. In taste reactivity tests both Gly and MSG elicitingestive oral motor responses that increase with stimulus concentrationin the absence of aversive behavior. The opposite responseswere obtained using long-term intake tests; MSG and Gly preferenceratios actually decrease with increasing concentration. Thesedata suggest a reinterpretation of standard, longterm intaketests. Specifically, effects of taste versus post-oral stimulimay be distinguished by contrasting taste reactivity and two-bottlepreference tests. Differences in the pattern of oral motor behaviorselicited by the amino acid and glutamate compounds are alsodiscussed.     

Gustatory sensory cells express a receptor responsive to protein breakdown products (GPR92)

The ingestion of dietary protein is of vital importance for the maintenance of fundamental physiological processes. The taste modality umami, with its prototype stimulus, glutamate, is considered to signal the protein content of food. Umami was thought to be mediated by the heterodimeric amino acid receptor, T1R1 + T1R3. Based on knockout studies, additional umami receptors are likely to exist. In addition to amino acids, certain peptides can also elicit and enhance umami taste suggesting that protein breakdown products may contribute to umami taste. The recently deorphanized peptone receptor, GPR92 (also named GPR93; LPAR5), is expressed in gastric enteroendocrine cells where it responds to protein hydrolysates. Therefore, it was of immediate interest to investigate if the receptor GPR92 is expressed in gustatory sensory cells. Using immunohistochemical approaches we found that a large population of cells in murine taste buds was labeled with an GPR92 antibody. A molecular phenotyping of GPR92 cells revealed that the vast majority of GPR92-immunoreactive cells express PLCβ2 and can therefore be classified as type II cells. More detailed analyses have shown that GPR92 is expressed in the majority of T1R1-positive taste cells. These results indicate that umami cells may respond not only to amino acids but also to peptides in protein hydrolysates.     

Carbohydrate Effects on Amino Acid Transport by Trypanosoma equiperdum*

SYNOPSIS. Uptake of ¹⁴C-labeled alanine, glutamate, lysine, methionine, proline, and phenylalanine by Trypanosoma equiperdum during 2-minute incubations occurred by diffusion and membrane-mediated processes. Amino acid metabolism was not detected by paper chromatography of trypanosome extracts. Most of 18 carbohydrates tested for ability to alter amino acid transport neither changed nor significantly inhibited transport. Glucose, however, stimulated glutamate, lysine and proline transport; fructose stimulated lysine uptake and 2-deoxy-D-glucose increased phenylalanine and methionine absorption. No evidence was found that the carbohydrates acted by binding to amino acid transport “sites.” Glucose inhibition of alanine, phenylalanine, and methionine uptake was linked to glycolysis. The rapid formation of alanine from glucose stimulated alanine release and, when glycolysis was blocked, glucose no longer inhibited alanine transport. Methionine and phenylalanine release was also stimulated by glucose. Glucose changed the ability of lysine, glutamate, and proline to inhibit each others’uptake, indicating that certain amino acids are preferentially absorbed by respiring cells. Analysis of free pool amino acid levels suggested that some amino acid transport systems in T. equiperdum are linked in such a way to glycolysis as to control the cell concentrations of these amino acids.     

Coding of sweet,bitter, and umami tastes: different receptor cells sharing similar signaling pathways

Mammals can taste a wide repertoire of chemosensory stimuli. Two unrelated families of receptors (T1Rs and T2Rs) mediate responses to sweet, amino acids, and bitter compounds. Here, we demonstrate that knockouts of TRPM5, a taste TRP ion channel, or PLCbeta2, a phospholipase C selectively expressed in taste tissue, abolish sweet, amino acid, and bitter taste reception, but do not impact sour or salty tastes. Therefore, despite relying on different receptors, sweet, amino acid, and bitter transduction converge on common signaling molecules. Using PLCbeta2 taste-blind animals, we then examined a fundamental question in taste perception: how taste modalities are encoded at the cellular level. Mice engineered to rescue PLCbeta2 function exclusively in bitter-receptor expressing cells respond normally to bitter tastants but do not taste sweet or amino acid stimuli. Thus, bitter is encoded independently of sweet and amino acids, and taste receptor cells are not broadly tuned across these modalities.     

Inhibition of growth of cells in culture by L-phenylalanine as a model system for the analysis of phenylketonuria. I. Amino acid antagonism and the inhibition of protein synthesis

Phenylalanine in high concentrations inhibits the growth of mouse A9 cells. Protein synthesis is inhibited earlier and more severely than RNA or DNA synthesis. Phenylalanine inhibits the uptake and decreases the intracellular pool of several amino acids. Certain amino acids added in excess reverse the phenylalanine inhibition. The strongest reversing amino acids appear to function by excluding phenylalanine. The phenylalanine inhibition does not appear to be due to a deficiency of any amino acid, but to the high intracellular phenylalanine concentration and/or an amino acid imbalance resulting from the large ratio of phenylalanine to other amino acids.     

Effects of UV radiation on five marine microphytobenthic Wadden sea diatoms,isolated from the Solthörn tidal flat (Lower Saxony,southern North Sea) – Part II: changes in carbohydrate,amino acid and fatty acid composition

Benthic diatoms inhabiting intertidal flats face highly variable environmental conditions, due to changing water levels and exposure during low tide. The present study is the second part of a more extensive study of the adaptive potential of these species in response to varying UV radiations in the Solthörn tidal flat (Lower Saxony, southern North Sea). Five isolates (Achnanthes exigua, Amphora exigua, Cocconeis peltoides, Diploneis littoralis and Navicula digitoradiata), which were found in this area in high cell numbers in summer 2008, were used in semi-continuous cultures to study the physiological effects of UV-radiation (PAR [photosynthetically active radiation], PAR+UV-A, PAR+UV-B, PAR+UV-B+UV-A). For short- and long-term exposures (6 h, 30 days), the composition of intercellular carbohydrates, amino and fatty acids were analysed in exponential-phase cultures grown at a salinity of 30 in a 12?:?12 h light?:?dark cycle at 20?°C. Although all tested species showed distinct differences in their initial carbohydrate, amino and fatty acid compositions and in their responses to the different UV treatments, general response patterns could be identified. Overall physiological responses to short- and long-term UV treatments included the accumulation of proline as well as an increase in total carbohydrates and lipids, whereas significant differences in the composition of carbohydrates, amino and fatty acids occurred after long-term exposure to the UV treatments (P < 0.05). While UV-A exposure led to higher accumulations of phenylalanine, aspartic acid and saturated fatty acids, the response to UV-B long-term exposure included increases of galactose, mannose and unsaturated fatty acids in the cells. In both UV experiments there was a noteworthy accumulation of the amino acid tryptophan in most species. The combined UV-A+UV-B experiment showed a significant (P < 0.05) increase of aspartic acid, phenylalanine, galactose and saturated fatty acids in a majority of species. Overall, the results indicated significant differences in the physiological responses of the five diatom taxa during UV exposure, which suggests species-specific acclimation strategies that may explain the growth insensitivity towards at least short-term UV.