We realize that this is an extreme situation and the crucial question is, of course, whether or not effects of this kind are likely to play a significant role also in proteins. The overall concentration of a given aminoacid may vary considerably between different protein species (see e.g. Table II) but only rarely exceeds 10%. Locally, however, the concentration may be much higher. Glutamic acid, e. g. has a high probability to be located in a-helical regions — it is in fact the strongest a-helix “former” following the terminology of Chou and Fasman  — while some other amino acids are “forbidden” there. Such clustering might well increase the sensitivity relative to situations where the mean distance between the glutamic acid residues is larger. In myoglobin, which is predominantly a-helical, a clustering of glutamic acid residues is in fact observed  and this could explain the significantly increased sensitivity of this aminoacid in myoglobin (Fig. 1). This sensitivity is more adequately reflected by the increase in a- aminobutyric acid content, the main transformation product (Table I) of glutamic acid (see below), than by the decrease in glutamic acid-glutamine content.
The marine diatoms Bellerochea yucatanensis and Thalassiosira rotula were grown at different salinities (20/25, 35, and 40/45 %o salinity (S), respectively) under normal air (0.035 vol.% C 0 2). No significant variations in the percentage of gross photosynthetic products (e.g. total amino acids, sugar phosphates) were found as a function of salinity during growth. The bulk of the soluble 14 C-radioactivity was detected in amino acids. 14 C-labelling of glutamine increased mark edly with salinity. Low salt — grown algae are characterized by enhanced aminoacid pools, mainly of aspartic acid, asparagine and glutamine. It was found that the tested amino acids are not involved in osmoregulation.
The data presented here indicate the existence o f a control mechanism regulating the uptake o f amino acids into the liver cells which is expressed upon extended preincubation o f liver slices. Three lines of evidence suggest that the enhancement o f transport which is based on a reduction o f the aminoacid concentration for half-maximal transport velocity, can be attributed to a stimulation o f the A system: this is demonstrated by the inhibiting effect o f the omission of N a + during AIB uptake, by the inhi biting effect o f adding excess MeAIB to the medium in which AIB uptake was measured, and, further more, by the finding that the uptake o f cysteine, a specific substrate for system ASC in hepatocytes , is not affected by the prolonged preincubation period.
secretome of transformed cells, including melanoma. We have therefore investigated acetate, pyruvate and the aminoacid composition of the secretome of human melanoma cells representing the early slow (WM35, WM278, WM793b and VM21) and metastatic fast (A375, 518a2, 6F and WM8) growth phase in order to identify possible signalling components within these profiles. Proliferation assays and a principle component analysis revealed a stringent difference between the fast and slow growing melanoma cells. Moreover, upon inhibition of the mevalonate pathway, glutamic acid and alanine were identified as the central difference in the conditional media. A supplementation of the media with glutamic acid and the combination with alanine significantly accelerated the proliferation, migration and invasion of early stage melanoma cells, but not metastatic cells. Finally, the inhibition of the mevalonate pathway abolished the growth advantage of the melanoma cells in a time dependent manner. Taken together, these data corroborate a stage specific response in growth and aggressiveness to extracellular glutamic acid and alanine, indicative for microenvironmental signalling of individual amino acids.
Amino acids in proteins are generally assumed to occur as L-enantiomers. However certain mirror images (enantiomers, or epimers if several chiral centers are concerned) of the protein L-amino acids, named D-amino acids, do also occur in foods. Conversion of L-amino acids (L-AA) into the respective D-enantiomers (D-AA) in food protein might occur in food processing such as heating and roasting, especially under alkaline or acidic conditions; this would drastically alter the enzymic degradation in the digestive tract and lead to a significant loss of nutritional value. A variety of evidence studies have demonstrated that there are two main sources of D-aminoacid enrichment in diverse food. First, racemization by special treatment during food processing and, second, D-aminoacid formation due to bacterial activity during fermentation processes (Friedman, 1999). As a result of exposure of food proteins to heat and or strongly alkaline or acid condition will lead to two major chemical changes: considerable D-amino acids formation of food proteins (racemization or epimerization), and concurrent formation of cross-linked aminoacid. The possible consequence of aminoacid racemization has been reviewed in detail (Friedman, 1999).
After publication of this supplement [ 1 ], it was brought to our attention that abstract A333 contains a serious error.
The error is that in one of the formulas to calculate aminoacid absorption, the authors reported significant aminoacid adsorption to the filter membrane. However,
Structure 4 can be excluded from the discussion o f the chrom ophore o f the dye o f the ninhydrin- aminoacid color reaction. This com pound should absorb in the UV spectral region (see Table I) be cause the conjugated system is interrupted, and the five-membered rings have no anti-aromatic char acter.
In case of pyrimidine metabolism, it was shown that pyrimidine homeostasis is accomplished by directed overflow metabolism. Increased pyrimidine pathway flux triggers degradation of the intermediate uridine monophosphate and allows homeostasis of pyrimidine triphosphates at the expense of uracil excretion (Reaves et al., 2013). It is unclear if cells use a similar strategy for maintenance of aminoacid homeostasis. It is known that E. coli is subject to degradation pathways for 12 of the 20 amino acids, which might be potential routes for a mechanism similar to pyrimidine overflow metabolism (Biocyc, RegulonDB). Generally aminoacid degradation pathways are considered as sources for nitrogen, carbon and energy (Reitzer, 2005). A well described example is the arginine degradation pathway (AST-pathway), which converts one molecule arginine to two molecules of ammonia and glutamate and can provide E. coli’s total nitrogen requirement (Schneider, Kiupakis and Reitzer, 1998). The AST-pathway consists of five enzymes whose genes are organized in an operon under positive control of the arginine repressor ArgR (Kiupakis and Reitzer, 2002). ArgR activates expression of the AST-operon in response to increased arginine level. Deletion of ast-genes (astB and astC) only caused a growth phenotype when arginine was used as the only nitrogen source, indicating that the prior role of the AST-pathway consists in nitrogen supply. However, it is unclear if degradation pathways like the AST-pathway could also be important in end-product maintenance, especially under such conditions of intra-cellular arginine excess.
On the contrary, the cerebral uptake of radiolabeled amino acids is low while it is typically increased in brain tumors, resulting in an enhanced tumor-to-background contrast [ 4 , 5 ]. Importantly, the uptake of aminoacid tracers is independent of the blood-brain barrier integrity, allowing the evaluation of aminoacid uptake in non-enhancing gliomas [ 1 , 6 ]. Additionally, aminoacid PET has demonstrated its usefulness for the differentiation of tumor progression from treatment-related changes [ 7 – 12 ] and for various other indications, e.g., treatment monitoring, prognostication or tumor grading [ 4 – 6 , 13 – 17 ]. Among aminoacid tracers labelled with carbon-11 used for PET imaging in neuro-oncology, [ 11 C]-methyl-L-methionine (MET) is currently best evaluated [ 18 , 19 ]. However, the short half-life of carbon-11 (20 min) limits its use to centers with an on-site cyclotron. To overcome such logistical limitations, aminoacid tracers have been labeled with fluorine-18, which has a longer half-life of 110 min [ 4 , 6 ]. For that reason, O-(2-[ 18 F]-fluoroethyl)-L-tyrosine (FET) has replaced MET in many neuro-oncological centers. Subsequently, FET has become the most widely used radiotracer for brain tumor diagnostics, especially in Western Europe. Another fluorine-18 labeled aminoacid tracer is 3,4-dihydroxy-6-[ 18 F]-fluoro-L-phenylalanine (FDOPA), originally developed to evaluate the dopamine synthesis in the basal ganglia, which also shows increased uptake in brain tumors [ 20 , 21 ]. Although brain tumors distant to the striatum are depicted with high contrast, the high striatal uptake of FDOPA limits its usefulness for tumor delineation especially near the basal ganglia [ 22 , 23 ]. The Response Assessment in Neuro-Oncology (RANO) working group considers the additional value of aminoacid PET for brain tumor diagnostics as highly relevant and recommends its use at every stage of brain tumor management [ 24 ].
The reactions of benzoyl isothiocyanate with aminoacid ethyl esters (N-butyl glycine ethyl ester, (S)-(-)-proline ethyl ester) give N-benzoylthiocarbamoyl aminoacid ethyl esters. Apart from the expected N-benzoylthiocarbamoyl (S)-(-)-proline ethyl ester the racemic N-benzoyl thiocarbamoyl (/?)/(S)-proline ethyl ester is formed because of base catalyzed racemization of the educt (5')-(-)-proline ethyl ester during the reaction of (S)-(-)-proline ethyl ester hy drochloride with triethylamine. The structures of both compounds were established by X-ray crystal structure analysis and specific optical rotation measurements. The ligands yield neutral 2:1 chelates with Ni , Cu11, Pd 11 and Pt11. The carboxylic oxygen atoms are not involved in
about 20 minutes and highest intensities were observed in the perinuclear region of the cells. The unselective inhibitor of EAATs, DL-TBOA, seems to decelerate uptake at low concentrations but paradoxically increases uptake at higher concentration of dansylproline. Similarly, spiking of the probes with molecular excess of unlabelled proline had a similar effect on the uptake of dansylproline. In the presence of 10 mM proline, dansylproline uptake was enhanced in all concentrations. The increased uptake of dansylproline when an excess of proline is present may be to two relevant transporters, one with high affinity but low capacity and another with low affinity but high capacity. Unfortunately, the quantification of these uptake data revealed no statistical significance so further experiments are needed. In addition, usage of other inhibitors than DL-TBOA and cellular systems with only a single aminoacid transporter expressed may guide future experiments and studies and shed light onto the exact mechanism of proline uptake.
Although wort contains a wide range of 30 distinct nitrogen sources, not all of them support the growth of yeast to the same extent. For this reason, the uptake of amino acids in yeast is a highly regulated process through various aminoacid permeases whose transcriptional control takes place either by nitrogen catabolite repression (NCR) or by SPS plasma membrane aminoacid sensor system (Ssy1p-Ptr3p-Ssy5) (Crépin, 2012). Through these mechanisms, yeasts select preferred nitrogen compounds that support fast growth with doubling times of 2 h (asparagine, glutamine, and ammonium) or minor preferred ones leading to doubling times < 3 h (aspartate, alanine, serine, arginine, glutamate, phenylalanine and valine) over non-preferred ones that support slower growth with doubling time > 4 h (leucine, isoleucine, methionine, threonine, tryptophan, and tyrosine) (Godard, 2007). Those amino acids that support fast growth are consumed early compared to specific permeases under SPS mediated control mechanism. On the other hand, those aminoacid sources that support slow growth are consumed at a later stage under the control of NCR mechanism.
Dietary concentrations of proximate nutrients were analysed according to the VDLUFA official methods. CP was calculated as N × 6.25. Aminoacid analysis followed standard procedures (Naumann and Bassler, 1976) and was described in details by Rodehutscord et al. (2004). In brief, 250 mg of sample was weighed (equivalent to 10 mg N) and oxidised in an ice bath for 24 hours after addition of 5 mL freshly prepared performic acid reagent [mix of 0.5 mL hydrogen peroxide, 4.5 mL 88 % phenol formic acid solution (889 g formic acid, 111 g water, 4.73 g phenol) and 25 mg phenol]. Performic acid was decomposed thereafter with sodium metabisulphite (~ 0.9 g). Samples were then hydrolysed for 24 h at 110 ºC after the addition of 50 mL hydrochloric acid solution (6 M, containing 1 g phenol ⁄ l). After cooling to room temperature, citrate buffer (0.2 M, pH 2.20) was added and pH of samples was adjusted with hydrochloric acid and sodium hydroxide solution to 2.20. After mixing, samples were filtered through sintered glass membrane filters (0.20 µm). The pH was controlled again and adjusted with hydrochloric acid and sodium hydroxide solution to pH 2.20 if necessary. Norleucine was used as the external standard. After this sample treatment, the determination of histidine, tryptophan and tyrosine is not possible. AAs were separated and detected using an AA Analyser (Eppendorf LC3000), using different buffer solutions, and ninhydrin. Extinction was determined at 570 nm, with the exception of proline, which was measured at 440 nm.
Enhancement of the absorption rate or absorption efficiency is higher for those solvents with bigger heats of absorption. These solvents possess a higher capacity of absorbed carbon dioxide per cycle and require smaller equipment sizing to meet low pressure gas specifications. Alkanolamines are the state of the art solvents for carbon dioxide removal in petroleum refining, coal gasification and hydrogen production. The increase in interest of flue gas scrubbing to reduce carbon dioxide emissions has increased the interest back to aminoacid salt solvents due to their ionic nature. Chemical solvents with kinetic-limited operation conditions, either because of molecular structure or the loading range in the absorber may be promoted by adding absorption rate promoters. Fast-reacting alkanolamines are well known promoters. However, some may result unstable under post-combustion operation conditions. Weak oxyacids are proven to act as carbon dioxide hydration catalysts (Rou38). Their use in systems that operate close to equilibrium has been reported to be beneficial. The activation of aminoacid solvents has not been fully investigated yet.
Proso millets, just like other cereals, are dependent on the nutrients from the soil it grows on. Hence, the soil greatly influences nutritive properties of the harvested grains. To combat this, some samples were harvested in two consecu- tive years, to investigate if the aminoacid profiles change from one year to another. Samples were grown in the same fields with the same soil in both years. The fields were located in Italy and Austria and had varying growing condi- tions. Some fields were located close to the sea, others in the Alps. Some fields were in a valley, others on a hillside. This way, a realistic experimental set-up was ensured, as on the European market proso millet is always only available as a mixture from a variety of fields. As already mentioned in Sect. 3.1 , the samples harvested in the first year have a slightly higher amount of amino acids than the samples from the second year. However, this is not due to an increase of a specific aminoacid but related to an overall increase of aminoacid concentrations. Consequently, the soil influenced the amount of total amino acids (see Fig. 1 ), but did not change the profile (see Fig. 3 ). This indicates that the overall growing conditions were better in the second year, which promoted higher aminoacid abundances.
Both protection and sensitization of Mice C57BL against 60Co y-rays by sulfur-containing aminoacid derivatives — S-alkyl-L-cysteines, S-alkyl-2-methyl-DL-cysteines and their hydantoin deriva tives, and sulfoxides o f these compounds — were examined. DL-5-Allylthiomethyl-5-methylhydan- toin (150 mg/kg body weight) had a remarkable radioprotective effect. The survival ratio was 4.33 or above two times as much as that o f L-cysteine. On the other hand, its sulfoxide had a radiosensitizing effects; survival ratio, 0.333.
Typical performance testing and quality control protocols are based on analysis of periodic calibration check and/or reference samples or synthetic mixes. However, this cannot confirm the actual and real value of an unknown sample. A technique that can determine the quality of analytical results for each analyte is achieved by using qualifier ion monitoring as a fast and specific quality check. The advantage of this concept lies in monitoring the coelution-free, unbiased quantification in every single sample. Our method applies this concept to one of the first for bioanalytical LC-MS/MS for endogenous and small samples. Especially aminoacid butyl esters are well suited for the qualifier ion monitoring. The optimization of Q1 and Q3 masses established at least 2 MRM transitions for one analyte. The MRM transitions with the highest intensity were used for quantification, second and/or third transition were used as qualifier ions. Harder et al. show the MRM transitions of all analytes and internal standards (23). Due to butylation small molecules like alanine and glycine confirm a second MRM transition. Without butylation only one transition exists.
phases prior to the Protein World, especially when these are based on the analysis of the genetically encoded proteins. A typical example is the Thioester World hypothesis , which suggests formation of peptides before their ribosomal synthesis. Perhaps, the thioester world should be functionally similar to present day non-ribosomal peptide syntheses, which is performed by relatively large and cumbersome protein complexes . To criticize this view, we would like to note that the Thioester World hypothesis is primarily based on side reactivity modes of aminoacyl-tRNA synthetases (aaRSs) and analysis of existing protein sequences . However, it was never explained how these proteins could exist before they were encoded by an mRNA. Indeed, many believe that aaRSs and other ribosomal proteins are among the oldest proteins, and their analysis can deliver valuable information about evolutionary past, for example, on how some principles of the protein fold and reactivity were developing [13,14]. However, if a hypothesis suggests existence of aaRSs before the Protein World (before they were coded by the mRNA), this means that the information somehow reverted from protein to nucleic acid. At the same time, there is no mechanism by which any hypothetical pre-ribosomal protein could encode itself into a nucleic acid, as such an event is directly forbidden by the Central Dogma . Any suggestion that proteins existed before coding, and then these ‘somehow’ ended up in the mRNA generates a severe logical contradiction: why do we accept the RNA World hypothesis from the Central Dogma, but neglect that the Central Dogma literally forbids any protein-to-RNA and protein-to-protein information flow? The question is of course rhetoric. For that reason, we believe that current phylogenetic analyses have rather limited significance in understanding of the phases prior the mature Protein World, before the genes received their complete protein meanings via the aminoacid assignment. Thus, speculations based on chemical logic can be much more informative than formal and rather speculative positivistic analyses of existent genes or protein sequences.