Postprandially, amino acids and di/tripeptides are thought to be primarily absorbed in the proximal small intestine. However, there have been no in vivo demonstrations of regional differences in amino acid transport dynamics between the proximal and distal small intestines. We monitored plasma amino acid responses in the jejunal and ileal mesenteric veins of rats after oral administration of a diet or an amino acid mixture (Expt 1) and in the portal vein after direct administration of the amino acid mixture into the lumen of the jejunum or ileum (Expt 2). In Expt 1, the total and some amino acid concentrations in the jejunal mesenteric vein were slightly higher than those in the ileal mesenteric vein after oral administration of the amino acid mixture, suggesting that the ileum actively transports luminal amino acids to the basolateral side, comparable to the jejunum. In Expt 2, portal amino acid concentrations were elevated to a greater extent after direct administration of the amino acid mixture into the ileal lumen than into the jejunal lumen. These results demonstrate regional differences in amino acid transport dynamics in vivo and suggest that the ileum has a higher capacity for transporting amino acids than the jejunum. Our findings highlight the importance of the ileum in postprandial amino acid absorption and metabolism.

The reaction between the herbicide “Roundup,” (PAH)3G, which is the commercial name of the iso-propylammonium salt of glyphosate (H3G, N-phosphonomethyl glycine), and montmorillonite was studied. The adsorption of the anionic component of Roundup glyphosate anion, G−3, from an ethanol solution is achieved by repeated immersion of the clay film in the alcohol solution followed by drying for 6–12 hr after each immersion. During the adsorption process the surface acidity of the interlayer space must be sufficiently high to protonate the anion. A zwitterion glyphosate is thereby formed in the interlayer space. Association forms are obtained in the interlayer space in which the COOH and the PO3H groups are linked to the exchangeable cations through water bridges. Adsorption of the glyphosate anion from aqueous solution of Roundup occurs when this anion forms a neutrally or positively charged complex with the exchangeable cation. This may occur with Al- and Fe-montmorillonite, when the molar ratio glyphosate:metal is such that a complex with a 1:1 ratio can be formed in the interlayer space. To clarify the reaction mechanism, adsorption of glycine by montmorillonite from ethanol solution was also studied. The associations obtained between glyphosate and exchangeable cations are less variable than those obtained between glycine and exchangeable cations in the interlayer space of montmorillonite. The following species of adsorbed glycine were identified: glycinium cation, zwitterion glycine, glycine complexed with metal cations either as a monodentate or as a bidentate ligand. In the latter case a chelate is formed.

The adsorption of Cu2+ on microcrystalline gibbsite and boehmite from aqueous solutions having 2/1 and 5/1 glycine/Cu ratios has been studied using electron spin resonance (ESR). The presence of glycine inhibited metal adsorption on gibbsite above pH 5, apparently by reducing Cu hydrolysis. The preferred adsorbed species on gibbsite and boehmite, based upon the ESR parameters, were probably Cu(gly)+ and Cu(gly)20, respectively. In both experiments, rigidly-bound ternary complexes formed with Cu2+ simultaneously bonding to the surface and one or more ligands. A large excess of glycine destabilized the ternary complex and caused the desorption of Cu2+. The preferred orientation of the Cu complex on gibbsite suggests that the adsorption occurred at crystal steps and that the glycine molecule hydrogen bonded to hydroxyls of the (001) surface.

The catalytic power of Ca-nontronite (0.2–2 μm) for the polycondensation of phenols and glycine and the associated reactions that involve the ring cleavage of phenols and the decarboxylation and deamination of glycine was studied in systems free of microbial activity. At the end of a 90-hr reaction period, the amount of CO2 released from the Ca-nontronite-glycine-pyrogallol, Ca-nontronite-glycine-eatechol, and Ca-nontronite-glycine-hydroquinone systems were 5.1, 8.7, and 11.6 times higher, respectively, than those from the respective nontronite-free systems, showing the catalytic role of Ca-nontronite in the ring cleavage of phenols and the decarboxylation of glycine. The release of CO2 and NH3 from the Ca-nontronite-glycine system revealed that Ca-nontronite can catalyze decarboxylation and deamination of glycine. The ability of Ca-nontronite to catalyze the deamination of glycine was substantially enhanced by the presence of a phenol. The visible absorbances at both 472 and 664 nm of the supernatants, the total yields of N-containing humic polymers, and the fractions of glycine converted to nitrogenous polymers indicated that polycondensation of glycine and phenol was greatly catalyzed by Ca-nontronite. The total N-containing humic polymers formed in the systems decreased in the order: Ca-nontronite-glycine-pyrogallol > Ca-nontronite-glycine-cateehol > Ca-nontronite-glycine-hydroquinone > glycine-pyrogallol > glycine-hydroquinone > glycine-catechol. The infrared and electron spin resonance spectra of humic acid (HA) and fulvic acid (FA) formed in the supernatants of the reaction systems were quite similar to those of soil HA and FA. The catalytic power of Ca-nontronite in affecting the ring cleavage of phenols, deamination and decarboxylation of amino acids, and formation of humic substances derived from phenols with amino acids in soils and the related environments thus merits attention.

Intracellular levels of glutathione, the major mammalian antioxidant, are reported to decline with age in several species. To understand whether ageing affects circulating glutathione levels in cats, blood was sampled from two age groups, < 3 years and > 9 years. Further, to determine whether dietary supplementation with glutathione precursor glycine (GLY) affects glutathione concentrations in senior cats (> 8 years), a series of free GLY inclusion level dry diets were fed. Subsequently, a 16-week GLY feeding study was conducted in senior cats (> 7 years), measuring glutathione, and markers of oxidative stress. Whole blood and erythrocyte total, oxidised and reduced glutathione levels were significantly decreased in senior cats, compared with their younger counterparts (P ≤ 0·02). The inclusion level study identified 1·5 % free GLY for the subsequent dry diet feeding study. Significant increases in erythrocyte total and reduced glutathione were observed between senior cats fed supplemented and control diets at 4 weeks (P ≤ 0·03; maximum difference of 1·23 µM). Oxidative stress markers were also significantly different between groups at 8 (P = 0·004; difference of 0·68 nG/ml in 8-hydroxy-2'-deoxyguanosine) and 12 weeks (P ≤ 0·049; maximum difference of 0·62 nG/mG Cr in F2-isoprostane PGF2α). Senior cats have lower circulating glutathione levels compared with younger cats. Feeding senior cats a complete and balanced dry diet supplemented with 1·5 % free GLY for 12 weeks elevated initial erythrocyte glutathione and altered markers of oxidative stress. Dietary supplementation with free GLY provides a potential opportunity to restore age-associated reduction in glutathione in cats.

As a consequence of treatments with glycine solutions, glycine molecules enter the interlayer of both Ca- and Cd-rich montmorillonite. Measurements of d value suggest that at low glycine concentration (0.01 and 0.1 M glycine solutions) a “flat” arrangement of the glycine molecules occurs in the interlayer. In contrast, intercalation of more than one monolayer of glycine molecules occurs for the montmorillonite treated with a higher concentration of glycine (1 M glycine solution).

Interlayer complexation of glycine occurs only for the Cd-rich form of montmorillonite, whereas no complexation is observed for Ca-rich montmorillonite. Both nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) results suggest that the adsorbed glycine, which fully protonates in the interlayer of montmorillonite to give the GlyH2− species, interacts with the interlayer Cd2+ to form the CdGlyx complex mainly through the carboxylate group. The interlayer cadmium, present as both Cd2+ and CdCl−, is complexed by the ligand glycine. In contrast, the cadmium adsorbed on the external surfaces of montmorillonite does not interact with the ligand. Complexation of CdCl+ only occurs for large amounts of adsorption of glycine (e.g., for samples treated with 1 M glycine solution).

Low birth weight (LBW) neonates show impaired growth compared with normal birth weight (NBW) neonates. Glutamine (Gln) supplementation benefits growth of weaning piglets, while the effect on neonates is not sufficiently clear. We examined the effect of neonatal Gln supplementation on piglet growth, milk intake and metabolic parameters. Sow-reared pairs of newborn LBW (0·8–1·2 kg) and NBW (1·4–1·8 kg) male piglets received Gln (1 g/kg body mass (BM)/d; Gln-LBW, Gln-NBW; n 24/group) or isonitrogenous alanine (1·22 g/kg BM/d; Ala-LBW; Ala-NBW; n 24/group) supplementation at 1–5 or 1–12 d of age (daily in three equal portions at 07:00, 12:00 and 17:00 by syringe feeding). We measured piglet BM, milk intake (1, 11–12 d), plasma metabolite, insulin, amino acid (AA) and liver TAG concentrations (5, 12 d). The Gln-LBW group had higher BM (+7·5%, 10 d, P = 0·066; 11–12 d, P < 0·05) and milk intake (+14·7%, P = 0·015) than Ala-LBW. At 5 d, Ala-LBW group had higher plasma TAG (+34·7%, P < 0·1) and lower carnosine (–22·5%, P < 0·05) than Ala-NBW and Gln-LBW, and higher liver TAG (+66·9%, P = 0·029) than Ala-NBW. At 12 d, plasma urea was higher (+37·5%, P < 0·05) with Gln than Ala supplementation. Several proteinogenic AA in plasma were lower (P < 0·05) in Ala-NBW v. Gln-NBW. Plasma arginine was higher (P < 0·05) in Gln-NBW v Ala-NBW piglets (5, 12 d). Supplemental Gln moderately improved growth and milk intake and affected lipid metabolism in LBW piglets and AA metabolism in NBW piglets, suggesting effects on intestinal and liver function.

The performance of pigs is affected by the rate of nutrient absorption in the gastrointestinal tract, which depends in turn strongly on the rate of stomach emptying. The 13C breath test provides a non-invasive diagnostic tool to measure gastric emptying patterns. Despite the wide acceptance of this method in human intervention studies, it has not found its way to the domain of animal sciences. In this study, we used the breath test to measure gastric emptying in young growing pigs using [1-13C] octanoic acid to trace digesta solids and [1-13C] glycine to study liquids. Pigs were fed a starch-rich diet, varying in starch source (isolated starch from barley, maize or high-amylose maize) or form (isolated barley starch, ground barley or extruded barley), after which 13CO2 enrichment was frequently measured during 11 h. Outliers in 13CO2 enrichment in the response curve of each pig were identified with a Cookʼs distance outlier test in combination with a leave-one-out analysis. Effects of experimental treatments on breath test parameters were tested using a GLM. In general, pigs were easy to train and the tailor-made mask allowed effortless sampling. Gastric emptying of all pigs followed a biphasic pattern, with a higher 13C recovery during the first peak. The first peak in gastric emptying of solids reached its maximum enrichment within 2 h after feeding in all cases. For digesta liquids, this peak was reached earlier for pigs fed ground barley (2.2 h after feeding), compared to pigs fed diets containing isolated starch (2.8 h after feeding). The second peak in gastric emptying of solids was reached later for pigs fed ground barley (5.9 h after feeding), compared with pigs fed extruded barley (4.5 h after feeding) and pigs fed diets containing isolated barley starch (4.8 h after feeding). In conclusion, the 13C breath test is a convenient, non-invasive tool to gain more insights into the gastric emptying pattern of pigs.

During adaptation to an increase in environmental luminance, retinal signaling adjustments are mediated by the neuromodulator dopamine. Retinal dopamine is released with light and can affect center-surround receptive fields, the coupling state between neurons, and inhibitory pathways through inhibitory receptors and neurotransmitter release. While the inhibitory receptive field surround of bipolar cells becomes narrower and weaker during light adaptation, it is unknown how dopamine affects bipolar cell surrounds. If dopamine and light have similar effects, it would suggest that dopamine could be a mechanism for light-adapted changes. We tested the hypothesis that dopamine D1 receptor activation is sufficient to elicit the magnitude of light-adapted reductions in inhibitory bipolar cell surrounds. Surrounds were measured from OFF bipolar cells in dark-adapted mouse retinas while stimulating D1 receptors, which are located on bipolar, horizontal, and inhibitory amacrine cells. The D1 agonist SKF-38393 narrowed and weakened OFF bipolar cell inhibitory receptive fields but not to the same extent as with light adaptation. However, the receptive field surround reductions differed between the glycinergic and GABAergic components of the receptive field. GABAergic inhibitory strength was reduced only at the edges of the surround, while glycinergic inhibitory strength was reduced across the whole receptive field. These results expand the role of retinal dopamine to include modulation of bipolar cell receptive field surrounds. Additionally, our results suggest that D1 receptor pathways may be a mechanism for the light-adapted weakening of glycinergic surround inputs and the furthest wide-field GABAergic inputs to bipolar cells. However, remaining differences between light-adapted and D1 receptor–activated inhibition demonstrate that non-D1 receptor mechanisms are necessary to elicit the full effect of light adaptation on inhibitory surrounds.

Sarcosine, which is freely sold as a dietary supplement, has pharmacological activity to boost functioning of the glutamatergic N-methyl-d-aspartate receptor (NMDAR) and hence it is a biologically rational treatment for schizophrenia. The small number of studies carried out to date provide some evidence for its efficacy and psychiatrists could consider suggesting its use to their patients.

This work deals with the formation of humic-like compounds, products of the Maillard reaction between glycine and D-glucose, on clay (K+, Ca2+ and Al3+-saturated montmorillonite and kaolinite) and quartz systems in the presence of the same cations. Natural quartz was used as the control while the effect of cation type, mineral substrate and CEC was evaluated. All the systems form humic-like substances that are probably responsible for the decrease in the pH (H2O) after 30 d. The type of cation does not influence the overall production of humic substances, while the amount of cations controls the formation of humic-like material especially in the presence of clays. A mineral surface is necessary to synthesize molecules with this high degree of complexity.

Fulvic-like compounds are produced in great amounts on natural quartz and their formation is hampered by the presence of ‘free’ cations, regardless of their amount. Humic substances do not penetrate the interlayer of montmorillonite.

The interactions between glycine and two Na-, Ca- and Cu-exchanged smectites with different layer-charge location were studied. The sorption of glycine depends on the nature of the interlayer cations (Ca < Na < Cu), and on the type of smectite. Sequential extraction procedures were carried out in order to test the possibility of removing metals and/or glycine from the smectite interlayer. By the end of the treatments, the release of the amino acid from the substrates, with the exception of Cu-rich smectite, was virtually complete. The thermal curves of glycine-smectites confirm the stronger bonding of the amino acid with Cu-exchanged samples, and FTIR spectra indicate that glycine is mainly sorbed in the zwitterionic form. The data obtained suggest that in investigations into mechanisms of the binding of metals by minerals and their subsequent mobilization, amino acids merit close attention.

Prebiotic chemical evolution on the early Earth may have been driven in part by fluctuating environments, for example wet‒dry and temperature cycling in volcanic rock pools. Here, we describe the setup, operating principle and test applications of a newly developed ‘wet‒dry apparatus’ (WDA) designed to simulate such fluctuating environments. The WDA allows adjusting the duration of the cycles, the temperature during the wet and dry phases and the organic and mineral components, which are all key parameters in wet–dry simulations. The WDA's most important features, however, are (i) that it is automated, which means that long-time experiments are possible without the need for an operator and (ii) that the virtual absence of free oxygen in the early Earth's atmosphere at ground level can be simulated. Rigorously oxygen-free conditions were achieved by passing 99.999% nitrogen gas through two alkaline pyrogallol solutions in series, prior to entering the WDA. We used three chemical systems to test the WDA: (i) the amino acid glycine in the presence and absence of clay minerals, (ii) linoleic acid (an oxygen-sensitive amphiphile) with and without the mineral olivine, and (iii) alkaline pyrogallol solution. We observed that clay minerals greatly accelerated the decomposition of glycine under wet‒dry conditions. Glycine peptides were formed as minor products. In the course of the glycine experiments, we developed a reliable gas chromatographic method to quantify the cyclic dipeptide 2,5-diketopiperazine. The decomposition of linoleic acid in wet‒dry cycles was promoted by both air and olivine. And finally, the extremely oxygen-sensitive pyrogallol solution was used as a colour indicator for residual oxygen in the WDA. The simulation facility in our laboratory currently consists of eight identical WDAs and a surrounding infrastructure. It can be made available to others who wish to perform cyclic wet–dry experiments.

Glyphosate [N-(phosphonomethyl)glycine] was separated from its potential metabolites, aminomethylphosphonic acid, glycine, and sarcosine by using 500 μm-thick cellulose plates developed with ethanol:water:15 N NH4OH:trichloroacetic acid (TCA):17 N acetic acid (55:35: 2.5:3.5 g:2, v/v/v/w/v with v in ml). This TLC system separated impurities from the 14C-glyphosate standard and glyphosate from possible metabolites in treated field bindweed (Convolvulus arvensis L.).

During the course of chemical evolution the role of metal oxides may have been very significant in catalysing the polymerization of biomonomers. The peptide bond formation of alanine (ala) and glycine (gly) in the presence of various oxides of manganese were performed for a period of 35 days at three different temperatures 50, 90 and 120°C without applying drying/wetting cycling. The reaction was monitored every week. The products formed were characterized by high-performance liquid chromatography and electrospray ionization–mass spectrometry techniques. Trace amount of oligomers was observed at 50°C. Maximum yield of peptides was found after 35 days at 90°C. It is important to note that very high temperatures of 120°C favoured the formation of diketopiperazine derivatives. Different types of manganese oxides [manganosite (MnO), bixbyite (Mn2O3), hausmannite (Mn3O4) and pyrolusite (MnO2)] were used as catalyst. The MnO catalysed glycine to cyclic (Gly)2, (Gly)2 and (Gly)3, and alanine, to cyclic (Ala)2 and (Ala)2. Mn3O4 also produced the same products but in lesser yield, while Mn2O3 and MnO2 produced cyclic anhydride of glycine and alanine with a trace amount of dimers and trimmers. Manganese of lower oxidation state is much more efficient in propagating the reaction than higher oxidation states. The possible mechanism of these reactions and the relevance of the results for the prebiotic chemistry are discussed.

Amacrine cells are a diverse set of local circuit neurons of the inner retina, and they all release either GABA or glycine, amino acid neurotransmitters that are generally inhibitory. But some types of amacrine cells have another function besides inhibiting other neurons. One glycinergic amacrine cell, the Aii type, excites a subset of bipolar cells via extensive gap junctions while inhibiting others at chemical synapses. Many types of GABAergic amacrine cells also release monoamines, acetylcholine, or neuropeptides. There is now good evidence that another type of amacrine cell releases glycine at some of its synapses and releases the excitatory amino acid glutamate at others. The glutamatergic synapses are made onto a subset of retinal ganglion cells and amacrine cells and have the asymmetric postsynaptic densities characteristic of central excitatory synapses. The glycinergic synapses are made onto other types of ganglion cells and have the symmetric postsynaptic densities characteristic of central inhibitory synapses. These amacrine cells, which contain vesicular glutamate transporter 3, will be the focus of this brief review.

In this work, the molecular interaction of the amino acid glycine and the mineral pyrite was performed to gain insight into the potential role of the mineral as a precursor of chemical complexity in the presence of ultraviolet (UV) radiation. Glycine samples were self-assembled on pyrite with and without exposure to UV radiation and subsequently characterized by scanning electron microscopy, infrared spectroscopy (with the second-derivative method), and AM1 and PM3 semi-empirical molecular computational simulations. In this work, our molecular modelling results suggest that pyrite acts as a template for self-assembly of glycine, and it is a potential catalyst for the glycine dimerization of relevance in interstellar space and ancient Earth conditions. A change in the structural complexity of glycine from the α to its γ polymorph when irradiated with UV radiation can be a condition for chemical evolution towards living forms.

During pregnancy, glycine and serine become more important because they are the primary suppliers of methyl groups for the synthesis of fetal DNA, and more glycine is required for fetal collagen synthesis as pregnancy progresses. In an earlier study, we reported that glycine flux decreased by 39 % from the first to the third trimester in pregnant adolescent girls. As serine is a primary precursor for glycine synthesis, the objective of this study was to measure and compare glycine and serine fluxes and inter-conversions in pregnant adolescent girls and adult women in the first and third trimesters. Measurements were made after an overnight fast by continuous intravenous infusions of 2H2-glycine and 15N-serine in eleven adolescent girls (17·4 (se 0·1) years of age) and in ten adult women (25·8 (se 0·5) years of age) for 4 h. Adolescent girls had significantly slower glycine flux and they made less glycine from serine in the third (P<0·05) than in the first trimester. Baby birth length was significantly shorter of adolescent girls (P=0·04) and was significantly associated with third trimester glycine flux. These findings suggest that the pregnant adolescent cannot maintain glycine flux in late pregnancy compared with early pregnancy because of decreased synthesis from serine. It is possible that the inability to maintain glycine synthesis makes her fetus vulnerable to impaired cartilage synthesis, and thus linear growth.

Receptive fields (RFs) of most retinal ganglion cells (RGCs) consist of an excitatory center and suppressive surround. The RF center arises from the summation of excitatory bipolar cell glutamatergic inputs, whereas the surround arises from lateral inhibitory inputs. In the retina, both gamma amino butyric acid (GABA) and glycine are inhibitory neurotransmitters. A clear role for GABAergic inhibition modulating the RGC RF surround has been demonstrated across species. Glycinergic inhibition is more commonly associated with RF center modulation, although there is some evidence that it may contribute to the RF surround. The synaptic glycinergic chloride channels are formed by three homomeric β and two homomeric α subunits that can be glycine receptor (GlyR) α1, α2, α3, or α4. GlyRα composition is responsible for currents with distinct decay kinetics. Their expression within the inner plexiform laminae and neuronal subtypes also differ. We studied the role of GlyR subunit selective modulation of RGC RF surrounds, using mice lacking GlyRα2 (Glra2−/−), GlyRα3 (Glra3−/−), or both (Glra2/3−/−). We chose this molecular genetic approach instead of pharmacological manipulation because there are no subunit selective antagonists and strychnine blocks all GlyRs. Comparisons of annulus-evoked responses among wild type (WT) and GlyRα knockouts (Glra2−/−, Glra3−/− and Glra2/3−/−) show that GlyRα2 inhibition enhances RF surround suppression and post-stimulus excitation in only WT OFF RGCs. Similarities in the responses in Glra2−/− and Glra2/3−/− RGCs verify these conclusions. Based on previous and current data, we propose that GlyRα2-mediated input uses a crossover inhibitory circuit. Further, we suggest that GlyRα2 modulates the OFF RGC RF center and surround independently. In summary, our results define a selective GlyR subunit-specific control of RF surround suppression in OFF RGCs.

The goals of these experiments were to describe the morphology and synaptic connections of amacrine cells in the baboon retina that contain immunoreactive vesicular glutamate transporter 3 (vGluT3). These amacrine cells had the morphology characteristic of knotty bistratified type 1 cells, and their dendrites formed two plexuses on either side of the center of the inner plexiform layer. The primary dendrites received large synapses from amacrine cells, and the higher-order dendrites were both pre- and postsynaptic to other amacrine cells. Based on light microscopic immunolabeling results, these include AII cells and starburst cells, but not the polyaxonal amacrine cells tracer-coupled to ON parasol ganglion cells. The vGluT3 cells received input from ON bipolar cells at ribbon synapses and made synapses onto OFF bipolar cells, including the diffuse DB3a type. Many synapses from vGluT3 cells onto retinal ganglion cells were observed in both plexuses. At synapses where vGluT3 cells were presynaptic, two types of postsynaptic densities were observed; there were relatively thin ones characteristic of inhibitory synapses and relatively thick ones characteristic of excitatory synapses. In the light microscopic experiments with Neurobiotin-injected ganglion cells, vGluT3 cells made contacts with midget and parasol ganglion cells, including both ON and OFF types. Puncta containing immunoreactive gephyrin, an inhibitory synapse marker, were found at appositions between vGluT3 cells and each of the four types of labeled ganglion cells. The vGluT3 cells did not have detectable levels of immunoreactive γ-aminobutyric acid (GABA) or immunoreactive glycine transporter 1. Thus, the vGluT3 cells would be expected to have ON responses to light and make synapses onto neurons in both the ON and the OFF pathways. Taken with previous results, these findings suggest that vGluT3 cells release glycine at some of their output synapses and glutamate at others.