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Journal: Amino acids


The postprandial rise in essential amino acid (EAA) concentrations modulates the increase in muscle protein synthesis rates after protein ingestion. The EAA content and AA composition of the dietary protein source contribute to the differential muscle protein synthetic response to the ingestion of different proteins. Lower EAA contents and specific lack of sufficient leucine, lysine, and/or methionine may be responsible for the lower anabolic capacity of plant-based compared with animal-based proteins. We compared EAA contents and AA composition of a large selection of plant-based protein sources with animal-based proteins and human skeletal muscle protein. AA composition of oat, lupin, wheat, hemp, microalgae, soy, brown rice, pea, corn, potato, milk, whey, caseinate, casein, egg, and human skeletal muscle protein were assessed using UPLC-MS/MS. EAA contents of plant-based protein isolates such as oat (21%), lupin (21%), and wheat (22%) were lower than animal-based proteins (whey 43%, milk 39%, casein 34%, and egg 32%) and muscle protein (38%). AA profiles largely differed among plant-based proteins with leucine contents ranging from 5.1% for hemp to 13.5% for corn protein, compared to 9.0% for milk, 7.0% for egg, and 7.6% for muscle protein. Methionine and lysine were typically lower in plant-based proteins (1.0 ± 0.3 and 3.6 ± 0.6%) compared with animal-based proteins (2.5 ± 0.1 and 7.0 ± 0.6%) and muscle protein (2.0 and 7.8%, respectively). In conclusion, there are large differences in EAA contents and AA composition between various plant-based protein isolates. Combinations of various plant-based protein isolates or blends of animal and plant-based proteins can provide protein characteristics that closely reflect the typical characteristics of animal-based proteins.


The aim of this study was to determine the effects of a caffeine-containing energy drink on physical performance during a rugby sevens competition. A second purpose was to investigate the post-competition urinary caffeine concentration derived from the energy drink intake. On two non-consecutive days of a friendly tournament, 16 women from the Spanish National rugby sevens Team (mean age and body mass = 23 ± 2 years and 66 ± 7 kg) ingested 3 mg of caffeine per kg of body mass in the form of an energy drink (Fure®, ProEnergetics) or the same drink without caffeine (placebo). After 60 min for caffeine absorption, participants performed a 15-s maximal jump test, a 6 × 30 m sprint test, and then played three rugby sevens games against another national team. Individual running pace and instantaneous speed during the games were assessed using global positioning satellite (GPS) devices. Urine samples were obtained pre and post-competition. In comparison to the placebo, the ingestion of the energy drink increased muscle power output during the jump series (23.5 ± 10.1 vs. 25.6 ± 11.8 kW, P = 0.05), running pace during the games (87.5 ± 8.3 vs. 95.4 ± 12.7 m/min, P < 0.05), and pace at sprint velocity (4.6 ± 3.3 vs. 6.1 ± 3.4 m/min, P < 0.05). However, the energy drink did not affect maximal running speed during the repeated sprint test (25.0 ± 1.5 vs. 25.0 ± 1.7 km/h). The ingestion of the energy drink resulted in a higher post-competition urine caffeine concentration than the placebo (3.3 ± 0.7 vs. 0.2 ± 0.1 μg/mL; P < 0.05). In summary, 3 mg/kg of caffeine in the form of a commercially available energy drink considerably enhanced physical performance during a women's rugby sevens competition.

Concepts: Mass, Caffeine, Running, Speed, Global Positioning System, Sprint, Rugby sevens, Commonwealth Games


Dietary intake of glutamate by postweaning pigs is markedly reduced due to low feed consumption. This study was conducted to determine the safety and efficacy of dietary supplementation with monosodium glutamate (MSG) in postweaning pigs. Piglets were weaned at 21 days of age to a corn and soybean meal-based diet supplemented with 0, 0.5, 1, 2, and 4 % MSG (n = 25/group). MSG was added to the basal diet at the expense of cornstarch. At 42 days of age (21 days after weaning), blood samples (10 mL) were obtained from the jugular vein of 25 pigs/group at 1 and 4 h after feeding for hematological and clinical chemistry tests; thereafter, pigs (n = 6/group) were euthanized to obtain tissues for histopathological examinations. Feed intake was not affected by dietary supplementation with 0-2 % MSG and was 15 % lower in pigs supplemented with 4 % MSG compared with the 0 % MSG group. Compared with the control, dietary supplementation with 1, 2 and 4 % MSG dose-dependently increased plasma concentrations of glutamate, glutamine, and other amino acids (including lysine, methionine, phenylalanine and leucine), daily weight gain, and feed efficiency in postweaning pigs. At day 7 postweaning, dietary supplementation with 1-4 % MSG also increased jejunal villus height, DNA content, and antioxidative capacity. The MSG supplementation dose-dependently reduced the incidence of diarrhea during the first week after weaning. All variables in standard hematology and clinical chemistry tests, as well as gross and microscopic structures, did not differ among the five groups of pigs. These results indicate that dietary supplementation with up to 4 % MSG is safe and improves growth performance in postweaning pigs.

Concepts: Protein, Amino acid, Essential amino acid, Glutamic acid, Excitotoxicity, Monosodium glutamate, Umami, Flavour enhancer


An efficient method for the synthesis of long-chain α,ω-diamino acids, starting from natural α-amino acids, has been developed. The long-chain skeleton has been generated through condensation between a protected aldehyde, derived from L-aspartic acid, and an ylide obtained from an ω-hydroxy-alkyl phosphonium salt. After conversion of the ω-hydroxy group into an amine, catalytic hydrogenation produced the N,N'-protected α,ω-diamino acid. The present route to α,ω-diamino acids allows the modulation of the chain length depending on the length of the ylide used for the Wittig olefination reaction.

Concepts: Amino acid, Acid, Hydrogen, Alkene, Aldehyde, Wittig reaction, Triphenylphosphine, Phosphonium salt


Ghrelin is a 28-residue peptide acylated with an n-octanoyl group on the Ser 3 residue, predominantly produced by the stomach. Ghrelin displays strong growth hormone (GH) releasing activity, which is mediated by the activation of the so-called GH secretagogue receptor type 1a (GHS-R1a). Given the wide spectrum of biological activities of Ghrelin in neuroendocrine and metabolic pathways, many research groups, including our group, developed synthetic peptide, and nonpeptide GHS-R1a ligands, acting as agonists, partial agonists, antagonists, or inverse agonists. In this highlight article, we will focus on the discovery of a GHS-R1a antagonist compound, JMV 2959, which has been extensively studied in different in vitro and in vivo models. We will first describe the peptidomimetic approach that led us to discover this compound. Then we will review the results obtained with this compound in different studies in the fields of food intake and obesity, addictive behaviors, hyperactivity and retinopathy.

Concepts: Protein, Hormone, Receptor, Growth hormone, Receptor antagonist, Agonist, Inverse agonist, Ghrelin


Alyteserin-2a (ILGKLLSTAAGLLSNL.NH(2)) is a cationic, amphipathic α-helical cell-penetrating peptide, first isolated from skin secretions of the midwife toad Alytes obstetricans. Structure-activity relationships were investigated by synthesizing analogs of alyteserin-2a in which amino acids on the hydrophobic face of the helix were replaced by L-tryptophan and amino acids on the hydrophilic face were replaced by one or more L-lysine or D-lysine residues. The Trp-containing peptides display increased cytotoxic activity against non-small cell lung adenocarcinoma A549 cells (up to 11-fold), but hemolytic activity against human erythrocytes increases in parallel. The potency of the N15K analog against A549 cells (LC(50) = 13 μM) increases sixfold relative to alyteserin-2a and the therapeutic index (ratio of LC(50) for erythrocytes and tumor cells) increases twofold. Incorporation of a D-Lys(11) residue into the N15K analog generates a peptide that retains potency against A549 cells (LC(50) = 15 μM) but whose therapeutic index is 13-fold elevated relative to the native peptide. [G11k, N15K] alyteserin-2a is also active against human hepatocarcinoma HepG2 cells (LC(50) = 26 μM), breast adenocarcinoma MDA-MB-231 cells (LC(50) = 20 μM), and colorectal adenocarcinoma HT-29 cells (LC(50) = 28 μM). [G11k, N15K] alyteserin-2a, in concentrations as low as 1 μg/mL, significantly (P < 0.05) inhibits the release of the immune-suppressive cytokines IL-10 and TGF-β from unstimulated and concanavalin A-stimulated peripheral blood mononuclear cells. The data suggest a strategy of increasing the cationicity while reducing the helicity of naturally occurring amphipathic α-helical peptides to generate analogs with improved cytotoxicity against tumor cells but decreased activity against non-neoplastic cells.

Concepts: Protein, Cell, Cancer, Amino acid, Red blood cell, Adenocarcinoma, Cytotoxicity, Frog


The quality of wheat (Triticum aestivum L.) for making bread is largely due to the strength and extensibility of wheat dough, which in turn is due to the properties of polymeric glutenin. Polymeric glutenin consists of high- and low-molecular-weight glutenin protein subunits linked by disulphide bonds between cysteine residues. Glutenin subunits differ in their effects on dough mixing properties. The research presented here investigated the effect of a specific, recently discovered, glutenin subunit on dough mixing properties. This subunit, Bx7.1, is unusual in that it has a cysteine in its repetitive domain. With site-directed mutagenesis of the gene encoding Bx7.1, a guanine in the repetitive domain was replaced by an adenine, to provide a mutant gene encoding a subunit (MutBx7.1) in which the repetitive-domain cysteine was replaced by a tyrosine residue. Bx7.1, MutBx7.1 and other Bx-type glutenin subunits were heterologously expressed in Escherichia coli and purified. This made it possible to incorporate each individual subunit into wheat flour and evaluate the effect of the cysteine residue on dough properties. The Bx7.1 subunit affected dough mixing properties differently from the other subunits. These differences are due to the extra cysteine residue, which may interfere with glutenin polymerisation through cross-linkage within the Bx7.1 subunit, causing this subunit to act as a chain terminator.

Concepts: Protein, Protein structure, Amino acid, Escherichia coli, Wheat, Protein subunit, Bread, Flour


Melanoma is the most malignant type of all skin neoplasms. Its worldwide incidence has steadily increased during the past decades, suggesting a probable melanoma ‘epidemic’. Although current clinical, morphologic, and histopathologic methods provide insights into disease behavior and outcome, melanoma is still an unpredictable disease. Once in an advanced stage, it remains a disastrous affliction with scarce therapeutic options. Therefore, significant efforts need to be made in finding informative biomarkers or surrogate markers that could aid or improve early diagnosis of melanoma, its correct staging, the discrimination of other pathological conditions as well as indicate patients' prognosis or the most appropriate therapeutic regimes. Ideally these markers are secreted into body fluids and easily amenable to the design of non-invasive clinical tests. A critical view on the current debate on serologic protein markers, e.g., lactate dehydrogenase, tyrosinase, and melanoma inhibiting activity, and some selected non-protein markers, e.g., 5-S-cysteinyl-dopa and circulating nucleic acids, will be offered and novel innovative approaches currently being explored will be discussed. Special emphasis is put on the S100 family of calcium binding proteins that is more and more emerging as a potentially important group of both molecular key players and biomarkers in the etiology, progression, manifestation, and therapy of neoplastic disorders, including malignant melanoma. Notably, S100B and, possibly, other S100 proteins like S100A4 are assumed to fulfill requirements which make them strong biomarker candidates in melanoma. Moreover, S100 proteins receive attention as possible targets of therapeutic intervention moving closer to clinical impact.

Concepts: Epidemiology, Cancer, Medical terms, Pathology, Neoplasm, Melanoma, Skin cancer, S-100 protein


PREFACE: This is the third special issue focused on “Transglutaminases” that is now available on this journal and dedicated to one of the pioneers of these enzymes, John Edward Folk, who died December 2010 [see in this issue Beninati et al. 2012a]. The first edition, “Polyamines and Transglutaminases” was published in Amino Acids, vol 26, no. 4, 2004, with the contribution of two prestigious Guest Editors as Alberto Abbruzzese and Mauro Piacentini. This editorial initiative was followed by the second special issue published in occasion of the 50th years of the discovery of transglutaminase. Indeed, “Transglutaminase 2: 50th Anniversary of the Discovery” Amino Acids, vol 36, no. 4, 2009, was published with the valuable collaboration of Carlo Maria Bergamini and Mauro Piacentini (Beninati et al. 2009). To continue with this editorial tradition, on this occasion, an outstanding board of Guest Editors composed by Francesco Facchiano and Mauro Piacentini has also been invited to promote this initiative and recruit a selected panel of Authors, many of who participated in the first and second edition of the Gordon Conference on Transglutaminases: “Transglutaminases in Human Diseases Processes” chaired by Rickard L Eckert and Kapil Mehta on July 18-23, 2010, and by Kapil Mehta and Mauro Piacentini on July 15-20, 2012, held at Davidson College, NC, USA. In this Amino Acids special issue, the manuscripts were selected to reflect the progress and the future perspectives of transglutaminases.

Concepts: Disease, Amino acid, Acid, Amine, Ammonia, Future, 1920, Transglutaminase


Indoleamine 2,3-dioxygenase-2 (IDO2) is one of three enzymes (alongside tryptophan 2,3-dioxygenase and indoleamine 2,3-dioxygenase (IDO1)) that catalyse dioxygenation of L-tryptophan as the first step in the kynurenine pathway. Despite the reported expression of IDO2 in tumours, some fundamental characteristics of the enzyme, such as substrate specificity and inhibition selectivity, are still to be clearly defined. In this study, we report the kinetic and inhibition characteristics of recombinant human IDO2. Choosing from a series of likely IDO2 substrates, we screened 54 tryptophan derivatives and tryptophan-like molecules, and characterised the 8 with which the enzyme was most active. Specificity of IDO2 for the two isomers of 1-methyltryptophan was also evaluated and the findings compared with those obtained in other studies on IDO2 and IDO1. Interestingly, IDO2 demonstrates behaviour distinct from that of IDO1 in terms of substrate specificity and affinity, such that we have identified tryptophan derivatives that are mutually exclusive as substrates for IDO1 and IDO2. Our results support the idea that the antitumour activity of 1-Me-D-Trp is unlikely to be related with competitive inhibition of IDO2, and also imply that there are subtle differences in active site structure in the two enzymes that may be exploited in the development of specific inhibitors of these enzymes, a route which may prove important in defining their role(s) in cancer.

Concepts: Enzyme kinetics, Enzyme, Enzyme substrate, Product, Catalysis, Enzyme inhibitor, Tryptophan, Biomolecules