New isoxazolinone amino acids from Lathyrus odoratus seedlings

In addition to β-(isoxazolin-5-one-2-yl)-alanine (I) and β-(2-β-D-glucopyranosyl-isoxazolin-5-one-4-yl)-alanine (III), previously found in Pisum sativum seedlings, two new amino acids and an amine containing the same heterocyclic ring have been isolated from Lathyrus odoratus seedlings. Their structures were determined as α-amino-γ-(isoxazolin-5-one-2-yl)-butyric acid (VI), 2-aminoethyl-isoxazolin-5-one (VII) and the γ-glutamyl derivative of the latter (V).     

Free amino acids from pollens

Pollens from Pinus canariensis, P. nigra, P. pinaster, P. pinea, Castanea sativa, Magnolia grandiflora, Olea sativa cv frantoio, cv itrana, cv pisciottana were examined for their free amino acid composition. A large amount of proline was found in all species; pollens of Olea also contain a large amount of serine.     

New triterpene saponins from the roots of Acacia macrostachya (Mimosaceae)

Four new oleanane-type saponins, macrostachyaosides A, B, C, and D (1–4) were isolated from the roots of Acacia macrostachya. Their structures were elucidated on the basis of extensive 1D- and 2D-NMR data and HR-ESI-MS analyses. At concentrations of 100 μM of each compounds, none of the tested compounds caused a significant growth reduction against HL60 cells.     

Biosynthesis of amino acids from hydrocarbons

Optimum conditions for the growth ofPseudomonas arvilla, a hydrocarbon utiliser, have been studied. The microorganism produced economic cell yield at pH 5.7 and 4% kerosene concentration. C₁₀-C₁₆ hydrocarbons were utilised by the strain. The growth was maximum on n-decane. Supplementation of the hydrocarbon medium with 0.5% glucose stimulated the growth. Glutamic acid 16.0 mg; leucine 9.0 mg; valine 10.0 mg; methionine 2.5 mg; arginine 2.5 mg; histidine 1.0 mg were present in 100 ml of the broth. Cell protein contained leucine 13.69%, isoleucine 4.9%, histidine 4.37%, tryptophan 2.33%, methionine 1.8% and arginine 2.70%.     

Mycosporine-like amino acids from coral dinoflagellates

Coral reefs are one of the most important marine ecosystems, providing habitat for approximately a quarter of all marine organisms. Within the foundation of this ecosystem, reef-building corals form mutualistic symbioses with unicellular photosynthetic dinoflagellates of the genus Symbiodinium. Exposure to UV radiation (UVR) (280 to 400 nm) especially when combined with thermal stress has been recognized as an important abiotic factor leading to the loss of algal symbionts from coral tissue and/or a reduction in their pigment concentration and coral bleaching. UVR may damage biological macromolecules, increase the level of mutagenesis in cells, and destabilize the symbiosis between the coral host and their dinoflagellate symbionts. In nature, corals and other marine organisms are protected from harmful UVR through several important photoprotective mechanisms that include the synthesis of UV-absorbing compounds such as mycosporine-like amino acids (MAAs). MAAs are small (<400-Da), colorless, water-soluble compounds made of a cyclohexenone or cyclohexenimine chromophore that is bound to an amino acid residue or its imino alcohol. These secondary metabolites are natural biological sunscreens characterized by a maximum absorbance in the UVA and UVB ranges of 310 to 362 nm. In addition to their photoprotective role, MAAs act as antioxidants scavenging reactive oxygen species (ROS) and suppressing singlet oxygen-induced damage. It has been proposed that MAAs are synthesized during the first part of the shikimate pathway, and recently, it has been suggested that they are synthesized in the pentose phosphate pathway. The shikimate pathway is not found in animals, but in plants and microbes, it connects the metabolism of carbohydrates to the biosynthesis of aromatic compounds. However, both the complete enzymatic pathway of MAA synthesis and the extent of their regulation by environmental conditions are not known. This minireview discusses the current knowledge of MAA synthesis, illustrates the diversity of MAA functions, and opens new perspectives for future applications of MAAs in biotechnology.     

Endogenous mutagens derived from amino acids

L-Cysteine, glutathione and the therapeutically used L-cysteine precursor, N-acetyl-L-cysteine, induced strong mutagenic effects in Salmonella typhimurium (reversion of the his- strains TA97, TA92 and TA104), when tested in the presence of subcellular kidney preparations. The tyrosine metabolites, levodopa (an ortho-hydroquinone) and homogentisic acid (a para-hydroquinone) reverted various his- strains as well. This mutagenicity did not require the presence of mammalian enzymes, and was relatively weak. The induction of gene mutations was also studied in mammalian cells (V79 Chinese hamster cells), using acquisition of resistance toward 6-thioguanine as the marker. L-Cysteine and N-acetyl-L-cysteine were found to be inactive, levodopa was weakly mutagenic, and homogentisic acid was strongly mutagenic (enhancing the mutation frequency 135-fold above background at an exposure concentration of 50 microM). This finding is striking as the urinary concentration of homogentisic acid is about 1000 times higher in patients with a genetic defect in homogentisic acid 1,2-dioxygenase (alkaptonuria). Genotoxic and carcinogenic effects of other amino acids and metabolites, reported in the literature, are discussed as well.     

l-threo- and l-erythro-2-amino-3-hydroxyhex-4-ynoic acids: New amino acids from Tricholomopsis rutilans

2-Amino-3-hydroxyhex-4-ynoic acid, reported previously from Tricholomopsis rutilans, was shown to be a mixture of its threo- and erythro-forms. They were separated from each other and characterized by elementary analysis, optical rotation, TLC, IR, NMR spectra, catalytic hydrogenation, and by chemical synthesis. Their configurations were determined by the comparison of their hydrogenation products with known threo- and erythro-2-amino-3-hydroxyhexanoic acids.     

Determining important regulatory relations of amino acids from dynamic network analysis of plasma amino acids

The changes in the concentrations of plasma amino acids do not always follow the flow-based metabolic pathway network. We have previously shown that there is a control-based network structure among plasma amino acids besides the metabolic pathway map. Based on this network structure, in this study, we performed dynamic analysis using time-course data of the plasma samples of rats fed single essential amino acid deficient diet. Using S-system model (conceptual mathematical model represented by power-law formalism), we inferred the dynamic network structure which reproduces the actual time-courses within the error allowance of 13.17%. By performing sensitivity analysis, three of the most dominant relations in this network were selected; the control paths from leucine to valine, from methionine to threonine, and from leucine to isoleucine. This result is in good agreement with the biological knowledge regarding branched-chain amino acids, and suggests the biological importance of the effect from methionine to threonine.     

Permeases recycle amino acids resulting from autophagy

Autophagy is a major survival mechanism for eukaryotes to recycle cellular nutrients during stress conditions (such as nutrient limitation, or the accumulation of damaged organelles). We recently revealed a molecular mechanism by which Atg22 recycles amino acids to link the degradative and recycling functions of autophagy. Atg22 is not directly required for autophagic body breakdown, in contrast to previously reported data. Instead, we found that Atg22, Avt3 and Avt4 are partially redundant vacuolar effluxers, which mediate the efflux of leucine and other amino acids resulting from autophagy.     

Locations of amino acids in brain slices from the rat. Tetrodotoxin-sensitive release of amino acids

1. Amino acids, particularly glutamate, gamma-aminobutyrate, aspartate and glycine, were released from rat brain slices on incubation with protoveratrine (especially in a Ca(2+)-deficient medium) or with ouabain or in the absence of glucose. Release was partially or wholly suppressed by tetrodotoxin. 2. Tetrodotoxin did not affect the release of glutamine under various incubation conditions, nor did protoveratrine accelerate it. 3. Protoveratrine caused an increased rate of formation of glutamine in incubated brain slices. 4. Increased K(+) in the incubation medium caused release of gamma-aminobutyrate, the process being partly suppressed by tetrodotoxin. 5. Incubation of brain slices in a glucose-free medium led to increased production of aspartate and to diminished tissue contents of glutamates, glutamine and glycine. 6. Use of tetrodotoxin to suppress the release of amino acids from neurons in slices caused by the joint action of protoveratrine and ouabain (the latter being added to diminish reuptake of amino acids), it was shown that the major pools of glutamate, aspartate, glycine, serine and probably gamma-aminobutyrate are in the neurons. 7. The major pool of glutamine lies not in the neurons but in the glia. 8. The tricarboxylic cycle inhibitors, fluoroacetate and malonate, exerted different effects on amino acid contents in, and on amino acid release from, brain slices incubated in the presence of protoveratrine. Fluoroacetate (3mm) diminished the content of glutamine, increased that of glutamate and gamma-aminobutyrate and did not affect respiration. Malonate (2mm) diminished aspartate and gamma-aminobutyrate content, suppressed respiration and did not affect glutamine content. It is suggested that malonate acts mainly on the neurons, and that fluoroacetate acts mainly on the glia, at the concentrations quoted. 9. Glutamine was more effective than glutamate as a precursor of gamma-aminobutyrate. 10. It is suggested that glutamate released from neurons is partly taken up by glia and converted there into glutamine. This is returned to the neurons where it is hydrolysed and converted into glutamate and gamma-aminobutyrate.     

Extraction of free amino acids from tomato leaves

Conditions for extraction of free amino acids from tomato leaves were examined. Two methods of sample preservation were also tested. Best results were obtained when samples were preserved by lyophilization and extracted by Soxhlet for 6 h at 40°C at a ratio of 1 g plant material/80 mL 80% (v/v) ethanol.     

Absorption of amino acids from the human mouth

Summary Certain amino acids were transported across buccal mucosa in vivo by a carrier-mediated process. Metabolic loss of L-amino acids from the mouth in a 5 min test period was negligible. The buccal mucosal transport process was stereospecific for most L-amino acids tested. The uptake of L-methionine and L-leucine showed a tendency to saturation with increasing substrate concentration. The absorption of L-leucine, L-isoleucine and L-methionine as single amino acids was inhibited in the presence of each other suggesting at least one common transport mechanism. Administration of equimolar amounts of amino acids revealed a specific pattern of absorption that could be classified into fast, intermediate, and slow groups. Absorption of some amino acids was at least partly dependent on the presence of sodium ions in the luminal solution. In conclusion, our studies demonstrate that the human buccal mucosa is permeable to L-amino acids in a selective manner, and may resemble absorption pattern similar to other locations of the gastrointestinal tract.This work was supported by Grant DK39147 from the National Institutes of Diseases and Digestive and Kidney Diseases, National Institutes of Health, United States Public Health Service, and The Lord Dowding Fund for Humane Research, London, U.K.     

Gluconeogenesis from amino acids in neonatal rat liver

1. The utilization of amino acids for gluconeogenesis by rat liver develops in postnatal life, reaching maximum activity at the fifth day. 2. The activity of aspartate transaminase shows a similar trend in postnatal development and the increased activity appears to be due to the soluble enzyme. 3. The activity of alanine transaminase is low in foetal and postnatal rat liver and increases in activity at about the twentieth day. 4. Aspartate, glutamate and alanine make a major contribution to gluconeogenesis in the postnatal rat liver.