Bioinspired amino acid-functionalized carbon dots nanozymes with enhanced peroxidase-like activity for sensitive detection of GSH in food.

Fractions of basic, neutral and acidic amino acids, and of neutral, phospho- and glyco-lipids were prepared from the amino acid- and the lipid-extracts obtained from the mid-gut gland of squid Todarodes pacificus. The basic amino acid- and the phospholipid-fractions induced a high behavioral feeding attraction activity for juvenile yellowtail Seriola quinqueradiata and the neutral amino acid- and the glycolipid-fractions did bring about a low activity.Of twenty-six authentic L- and DL-amino acids, the activities were found in histidine, arginine, lysine and ornithine among the basic amino acids. Especially, histidine and arginine strikingly induced an attraction behavior in the fish. In the neutral amino acids, glycine, valine, threonine, methionine and cystine were involved in the attraction, specially glycine and threonine showing high activity. In the acidic amino acids, asparatic acid and glutamic acid didn't show an activity, while their amides did. Both L-histidine and L-threonine elicited the attraction in contrast to D-types which showed little effects.Of thirty authentic lipids, the activities were high in many kinds of phospholipids. Among the other lipids, however, only palmitic acid and stearic acid, monostearin, and ceramide were effective.The threshold values were estimated to be 5×10-7 M and 6×10-8 M for L-histidine and egglecithin, respectively.

ABSTRACTThe influence of different pHs, ranging from 5.0 to 9.0, on the formation of pyrazines in the Maillard reaction of L‐ascorbic acid with acidic, basic and neutral amino acids was studied. The results clearly showed that pyrazine formation was favored at higher pH. These findings suggest that the formation of pyrazines is catalyzed by base. However, pH affects the formation of pyrazines at different degrees for neutral, acidic and basic amino acids. The pH has the greatest impact on acidic amino acids and the least impact on basic amino acids and the impact of pH on neutral amino acids is in between. L‐Cysteine behaves similar to acidic amino acids because of its weakly acidic mercapto group. Another finding is that the formation of some pyrazines is independent of the amino acid structure, and the amino acids are solely a nitrogen source and do not provide carbon skeletons. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

The application of neutral or acidic amino acids to oat coleptiles induced transient depolarizations of the membrane potentials. The depolarizations are considered to reflect H(+) -amino acid co-transport, and the spontaneous repolarizations are believed to be caused by subsequent electrogenic H(+) extrusion. The basic amino acids depolarized the cell membrane strongly, but the repolarizations were weak or absent. The depolarizations induced by the basic amino acids were weakly sensitive to manipulations of the extracellular and intracellular pH. The depolarizations induced by the other amino acids, in contrast, were more strongly affected by the pH changes. Several amino acids induced distinct but diminished depolarizations in the presence of 2,4-dinitrophenol or cyanide, but the repolarizations were generally eliminated. These experiments support the co-transport theory but suggest somewhat different mechanisms for the transport of the neutral, acidic, and basic amino acids. We suggest that the neutral amino acids are co-transported with a single H(+) and that accumulation depends upon both the DeltapH and the membrane potential components of the proton motive force. The acidic amino acids appear to be accumulated by a similar mechanism except that the transport of each molecule may be associated with a cation in addition to a single proton. The permanently protonated basic amino acids appear not to be co-transported with an additional proton. Accumulation would depend only on the membrane potential component of the proton motive force.

Subcellular fractionation of rat cerebral cortical slices on sucrose density gradients provides evidence for the existence of a unique synaptosomal fraction (enriched in pinched-off nerve endings) that selectively accumulates glutamic and aspartic acids. The particles in this fraction sediment to a less dense portion of sucrose gradients than do particles that accumulate aromatic, basic, and neutral (large and small) amino acids. Particles that store gamma-aminobutyric acid are even less dense than those that contain exogenous glutamic and aspartic acids. The distribution of endogenous glutamic acid encompasses both that of exogenous glutamic acid and that of the neutral and basic amino acids. These findings provide neurochemical support for the suggestion that glutamic and/or aspartic acid has a specialized synaptic function, perhaps as a neurotransmitter, in the mammalian brain.

The transport of several amino acids with different side-chain characteristics has been investigated in the aquatic liverwort Riccia fluitans. i) The saturation of system I (neutral amino acids) by addition of excess α-aminoisobutyric acid to the external medium completely eliminated the electrical effects which are usually set off by neutral amino acids. Under these conditions arginine and lysine significantly depolarized the plasmalemma. ii) L- and D-lysine/arginine were discriminated against in favour of the L-isomers. iii) Increasing the external proton concentration in the interval pH 9 to 4.5 stimulated plasmalemma depolarization, electrical net current, and uptake of [(14)C]-basic amino acids. iv) Uptake of [(14)C]-glutamic acid took place only at acidic pHs. v) [(14)C]-histidine uptake had an optimum between pH 6 and 5.5. vi) Overlapping of the transport of basic, neutral, and acidic amino acids was common. It is suggested that besides system I, a second system (II), specific for basic amino acids, exists in the plasmalemma of Riccia fluitans. It is concluded that the amino-acid molecule with an uncharged side chain is the substrate for system I, which also binds and transports the neutral species of acidic amino acids, whereas system II is specific for amino acids with a positively charged side chain. The possibility of system II being a proton cotransport is discussed.

Diurnal variations in plasma concentrations of basic and neutral amino acids and in red cell concentrations of aspartate and glutamate: effects of dietary protein intake

Dual-mode colorimetric and fluorescence sensing system for the detection of captopril based on Fe/NC nanozymes and carbon dots

The effects of intravenous infusions of a variety of neutral and acidic amino acids on the plasma concentrations and excretions of naturally occurring amino acids were studied in dogs. Conventional clearance techniques were used, and the amino acid concentrations were determined by ion exchange column chromatography. Infusion of either l-glutamic acid or l-aspartic acid caused a gross increase in the plasma concentration and excretion of the other. Infusions of neutral amino acids including glycine, l-alanine, l-leucine, l-methionine, l-proline, and l-phenylalanine caused some minor changes in the endogenous plasma amino acid concentrations. They produced increases in the excretion of other neutral amino acids and, in some cases, of acidic and basic amino acids as well. In general, amino acids with long side chains were most effective in inhibiting reabsorption while cyclic side-chain compounds were less effective. There appear to be at least three somewhat separable mechanisms for renal tubular reabsorption of amino acids in dogs.

This study successfully developed a colorimetric/SERS dual-mode sensor for determining acrylamide in baked goods based on the excellent peroxidase-like activity and Raman activity of Fe-PHS@Au-Ag-Au Janus NPs. In colorimetricmode, the thiol-ene Michael addition between acrylamide (AA) and glutathione (GSH) efficiently eliminates GSH-induced peroxidase-like activity inhibition. The peroxidase-like activity of Fe-PHS@Au-Ag-Au Janus NPs gradually recovered, and the blue colorof the solution gradually deepened with the increase in AA dosage. In surface-enhanced Raman spectroscopy (SERS), Apt-Fe-PHS@Au-Ag-Au Janus NPs can selectively capture AA and bind specifically, leading to the dissociation of Apt and Fe-PHS@Au-Ag-Au Janus NPs. The Raman activity of Apt-Fe-PHS@Au-Ag-Au Janus NPs decreases due to the dissociation of Apt. The dual-mode sensor was utilized for the determination of acrylamide in the concentrations range from 0.05 to 20µg·L-1 with detection limits of 0.06µg·L-1 (SERS) and 0.01µg·L-1 (colorimetric). The recovery in baked samples was between 91.0 and 108.0%.

Prokineticins are a pair of signal factors involved in many physiological processes by binding to two closely related G-protein-coupled receptors, PKR1 and PKR2. Recently, mutations in prokineticin 2 (PK2) and PKR2 are found to be associated with Kallmann syndrome and/or idiopathic hypogonadotropic hypogonadism, disorders characterized by delayed puberty and infertility. However, little is known how PKRs interact and activate G-proteins to elicit signal transduction. In the present study, we took advantage of one disease-associated mutation (R164Q) located in the second intracellular (IL2) loop of PKR2, to investigate the role of IL2 loop in the cell signaling, G-protein binding and receptor trafficking. R164Q mutant PKR2 showed normal cell surface expression and ligand binding capacity. However, the PKR2 signaling was abolished by R164Q mutation. We demonstrated that R164Q mutation disrupted the interaction of IL2 loop to the Gα(q), Gα(i), and Gα(16)-proteins. A positive-charged amino acid at this position is required for proper function, and the signaling efficacy and potency depend on the net amount of positive charges. We also demonstrated that the interactive partner of Arg-164 may localize in the C-terminal five residues of Gα(q)-protein. A series of mutation analysis indicated that the basic amino acids at the C terminus of IL2 loop may function cooperatively in GPCRs. Furthermore, R164Q mutation also results in minimal ligand-induced endocytosis of PKR2. As many GPCRs share structural homology in the C terminus of IL2 loop, our findings may have general application in understanding structure and function of GPCRs.

Bioinspired carbon dots (CDs) with excellent biocompatibility were prepared from egg white as precursors through a simple hydrothermal method at 200 °C for 4 hours. The obtained CDs exhibited bright blue fluorescence, excellent optical stability, and sensitive response to tetracycline. Under the optimized synthetic conditions, the fluorescence quantum yield is 17.6 %. The fluorescence intensity of CDs at 440 nm could be quenched linearly with the addition of tetracycline in the range of 0.1–200 μmol L −1 due to the internal filtering effect. The proposed detection platform has been applied in the determination of tetracycline in milk samples with good results. The limit of detection is 32.3 nmol L −1 , and the spiked recoveries are in the range of 93–103 %. Additionally, the CDs could also be applied to cell imaging, implying good biocompatibility and low toxicity. As a type of green and effective multi‐functional fluorescence materials, the CDs have potential applications in biochemical sensing and biomedical imaging.

Sites 790 and 791 lie in the eastern half graben of the Sumisu Rift, a backarc graben west of the active Izu-Bonin arc volcanoes Sumisu Jima and Tori Shima, at 30°54.96'N, 139°50.66Ti, in 2223 m water depth and 30°54.97'N, 139°52.20'E, in 2268 m water depth, respectively. A small decrease in the sulfate concentration in the interstitial waters from these sites suggests fairly low microbial activity by sulfate-reducing bacteria. The values of the dissolved free amino acids (DFAA) in the interstitial waters from both sites range from 1.26 to 6.82 µmol/L, with an average of 3.81 µmol/L. The acidic, basic, neutral, aromatic, and sulfur-containing amino acids have average values of 0.32, 0.50, 2.71, 0.15, and 0.09 µmol/L, respectively. The relative abundances of the acidic, basic, neutral, aromatic, and sulfur-containing amino acids average 8, 13,72,4, and 1 mol%, respectively. Glycine, serine, alanine, ornithine, and aspartic acid are major constituent amino acids. The dissolved combined amino acids (DCAA) values range between 1.25 and 44.35 µmol/L, with an average of 10.36 µmol/L. The mean concentrations and relative abundances of the acidic, basic, neutral, aromatic, and sulfur-containing amino acids are 2.29 (22 mol%), 0.60 (6 mol%), 6.70 (65 mol%), 0.09 (1 mol%), and 0.00 µmol/L (0 mol%), respectively. Glycine is the most abundant amino acid residue, followed by glutamic acid, serine, and alanine. The predominance of DCAA over DFAA present in the interstitial waters from Sites 790 and 791 is consistent with previous results from interstitial-water and seawater analyses. The most plausible source for the DCAA is biogenic calcareous debris. A much greater depletion of aspartic acid and the basic fraction, except for ornithine, is found in the DCAA. The decomposition of the basic amino acid fraction or its incorporation to clay minerals would result in a decrease in its relative abundance, whereas ornithine is produced during early diagenesis. The characteristics of the amino acids in the interstitial waters are (1) a greater depletion of the acidic amino acid fraction in the DFAA than in the DCAA and (2) the enrichment of glycine and serine in both. The adsorption or reaction of the amino acids in interstitial waters with biogenic carbonates would be responsible for the lower relative abundance of the acidic fraction of the DFAA. The production of glycine during early diagenesis and its stability in solution would raise its relative abundance in the interstitial waters.

Carbon dot (CD)-based multi-mode sensing has drawn much attention owing to its wider application range and higher availability compared with single-mode sensing. Herein, a simple and green methodology to construct a CD-based dual-mode fluorescent sensor from the waste biomass of flowers of wintersweet (FW-CDs) for parallel and semi-quantitative visual detection of Cr(VI) and Fe3+ was firstly reported. The FW-CD fluorescent probe had a high sensitivity to Cr(VI) and Fe3+ with wide ranges of linearity from 0.1 to 60 µM and 0.05 to 100 µM along with low detection limits (LOD) of 0.07 µM and 0.15 µM, respectively. Accordingly, the FW-CD-based dual-mode sensor had an excellent parallel sensing capacity toward Cr(VI) and Fe3+ with high selectivity and strong anti-interference capability by co-using dual-functional integration and dual-masking strategies. The developed parallel sensing platform was successfully applied to Cr(VI) and Fe3+ quantitative detection in real samples with high precision and good recovery. More importantly, a novel FW-CD-based fluorescent hydrogel sensor was fabricated and first applied in the parallel and semi-quantitative visual detection of Cr(VI) and ferrous ions in industrial effluent and iron supplements, further demonstrating the significant advantage of parallel and visual sensing strategies.

Preparation of carbon dots from succinic acid and glycerol as ferrous ion and hydrogen peroxide dual-mode sensors and for cell imaging

Electrical responses to 17 amino acids, taurine, betaine, acetic acid and HCI were recorded from the ramus buccalis wich innervates pit organs on the snout region of the carp. In the whole merve responses, L-glutamic acid and L-aspartic acid which belong to the group of the acidic amino acid elicited marked excitatory responses. Their threshold was estimated to be between 10-6M and 5×10-6M and was as low as that of HCI or acetic acid. Neutral amino acids except L-proline also induced excitatory responses, while their thresholds were 2-3 log units higher than those of the acidc amino acids. When the stimulus intensity was sufflciently high, the response was composed of two phases, the phasic and tonic phase. The stimulation with basic amino acids caused an inhibition of the spontaneous discharges. The inhibitory effect of L-arginine could be transformed into the excitatory when the pH was modified to 7.0. High dependence of the response uponth the pH was suggested. In twenty-seven fibers, responses to seven amino acids and HCI were recorded. All the fibers responded to all the chemicals tested but no specific fiber was found. High correlation coefficients among the responses to the chemicals were obtained in all the fibers. These results suggest that the pit organs innervated by the r. buccalis can respond to various chemicals, but theylack the function to differentiate the chemicals.