Development of Software Workflow for the Rapid Detection of Cross-Linked Dipeptides

Detection and characterization of cross-linked peptides of unknown chemical nature and location is challenging. An analytical workflow based on the use of ¹⁸O-labeling tryptic digestion ( Anal. Chem. 2013, 85, 5900-5908) was previously utilized to identify reduction-resistant scrambled disulfide dipeptides within an IgG that was exposed to light under forced degradation conditions ( Mol. Pharmaceutics 2018, 15, 1598-1606). The analytical workflow denoted as XChem-Finder, while effective, is cumbersome and requires extensive manual effort for detection of ¹⁸O-incorporated peptides and subsequent de novo sequencing of partial peptide sequences to aid in the identification of cross-linked peptides. Here, we provide an automatic workflow using Byos (Protein Metrics Inc.) to facilitate the detection of cross-linked peptides. The LC-MS/MS data files that were subjected to the XChem-Finder workflow that identified the scrambled disulfides were utilized as the test-case data set for the automated ¹⁸O-labeling workflow in Byos. The new workflow resulted in the detection of a photoinduced cross-linked dipeptide with unknown linker chemistry, which was subsequently identified as a cross-linked dipeptide with a novel cysteine-tryptophan (thioether) linkage. This work demonstrates that combining ¹⁸O-labeling tryptic digestion with the Byos workflow enables rapid detection of cross-linked dipeptides.

A Novel UPLC-MS/MS Method Identifies Organ-Specific Dipeptide Profiles

BACKGROUND

Amino acids have a central role in cell metabolism, and intracellular changes contribute to the pathogenesis of various diseases, while the role and specific organ distribution of dipeptides is largely unknown.

METHOD

We established a sensitive, rapid and reliable UPLC-MS/MS method for quantification of 36 dipeptides. Dipeptide patterns were analyzed in brown and white adipose tissues, brain, eye, heart, kidney, liver, lung, muscle, sciatic nerve, pancreas, spleen and thymus, serum and urine of C57BL/6N wildtype mice and related to the corresponding amino acid profiles.

RESULTS

A total of 30 out of the 36 investigated dipeptides were detected with organ-specific distribution patterns. Carnosine and anserine were most abundant in all organs, with the highest concentrations in muscles. In liver, Asp-Gln and Ala-Gln concentrations were high, in the spleen and thymus, Glu-Ser and Gly-Asp. In serum, dipeptide concentrations were several magnitudes lower than in organ tissues. In all organs, dipeptides with C-terminal proline (Gly-Pro and Leu-Pro) were present at higher concentrations than dipeptides with N-terminal proline (Pro-Gly and Pro-Leu). Organ-specific amino acid profiles were related to the dipeptide profile with several amino acid concentrations being related to the isomeric form of the dipeptides. Aspartate, histidine, proline and serine tissue concentrations correlated with dipeptide concentrations, when the amino acids were present at the C- but not at the N-terminus.

CONCLUSION

Our multi-dipeptide quantification approach demonstrates organ-specific dipeptide distribution. This method allows us to understand more about the dipeptide metabolism in disease or in healthy state.

Novel univariate spectrophotometric determination of the recently released solid dosage form comprising dapagliflozin and saxagliptin via factorized response spectra: Assessment of the average content and dosage unit uniformity of tablets

Dapagliflozin (DPF) and saxagliptin (SXG) are currently co-formulated in a tablet dosage form which is prescribed to improve glycemic control. The absorption spectra of DPF and SXG were highly overlapped which completely hindered their simultaneous estimation at their λ_max 224 nm and 209 nm, respectively. Thus, in this work three smart and simple univariate spectrophotometric methods were originally established and validated for the first time in order to quantitatively estimate DPF and SXG in bulk forms and in combined pharmaceutical formulation without the requirement for any initial separation or treatment. These methods are; factorized zero order method (FZM), factorized derivative method (FDM) and factorized ratio difference method (FRM). These methods were capable of determining DPF and SXG over the range of 2.5-50.0 μg/mL and 2.5-60.0 μg/mL, respectively. All the developed methods are based on a novel and unique approach for the spectral recovery of unresolved spectra named; factorized response spectrum (FRS). The exclusivity of the FRS originates from its ability to completely resolve the cited drugs in the mixture and retrieve their original spectra. Selectivity of all proposed methods was assessed by comparing the obtained results of the mixture analysis with those of the pure powdered drugs. Validation of the newly developed methods was applied as recommended by the ICH demonstrating acceptable accuracy and precision. In general, these methods could be effectively employed for the routine quality control investigation of bulk materials and available market formulations.

UV-vis sensor array combining with chemometric methods for quantitative analysis of binary dipeptide mixture (Gly-Gly/Ala-Gln)

Many endogenous peptides are circulating in bodily fluids at micromole level, and accurate analysis of endogenous peptides at such low level is important. In this study, we presented an extensible, facile and sensitive sensor array based on UV-Vis spectroscopy of the AuNPs combined with chemometric methods for quantitative analysis of binary peptide mixture (Gly-Gly/Ala-Gln) using UV-Vis spectroscopy. High concentration arginine (Arg) and Cr³⁺ can induce aggregation of the AuNPs and DNA-AuNPs. However, the glycylglycine (Gly-Gly) and alanyl-glutamine (Ala-Gln) can prevent the AuNPs from aggregation. We investigated the prevention of AuNPs aggregation by using Gly-Gly and Ala-Gln mixtures and constructed sensor arrays for quantitative analyses of Gly-Gly and Ala-Gln mixtures. The color change of the solution is relevant to the dose of the target, and it can be visualized by the naked eyes or monitored by UV-Vis spectrometry. Results showed that the concentrations of Arg and Cr³⁺ are the key factors affecting the sensitivity of the sensor array. Whereas when Gly-Gly and Ala-Gln have to be analyzed simultaneously, concentrations of Arg and Cr³⁺ both for Gly-Gly and Ala-Gln are difficult to be optimized. Taking the advantages of multivariate analysis and data fusion, PLS models and backward interval PLS (BiPLS) models were built for fused dataset constructed by UV-Vis data obtained at different concentrations of Arg and Cr³⁺. The best results were obtained from the PLS models. The proposed method can be extended to analysis of other peptides in more complex mixture systems.

Family-wide Annotation of Enzymatic Pathways by Parallel In Vivo Metabolomics

Enzymes catalyze fundamental biochemical reactions that control cellular and organismal homeostasis. Here we present an approach for de novo biochemical pathway discovery across entire mammalian enzyme families using parallel viral transduction in mice and untargeted liquid chromatography-mass spectrometry. Applying this method to the M20 peptidases uncovers both known pathways of amino acid metabolism as well as a previously unknown CNDP2-regulated pathway for threonyl dipeptide catabolism. Ablation of CNDP2 in mice elevates threonyl dipeptides across multiple tissues, establishing the physiologic relevance of our biochemical assignments. Taken together, these data underscore the utility of parallel in vivo metabolomics for the family-wide discovery of enzymatic pathways.

Nitrogen-Doped Hollow Copolymer Tube via Template-Free Asynchronous Polymerization with Highly Selective Separation of Hydrophilic Dipeptide for Enhancing Inhibitory Activity of Angiotensin Converting Enzyme

A N-doped hollow copolymer tube (NHCT) was fabricated via template-free one-pot asynchronous polymerization strategy. Discrepancies of monomer polymerization speed and their hydrophilic-hydrophobic interaction resulted in the assembly of a hollow tube having inner diameter and double wall thickness of ∼230 and 40 nm, respectively. The formation and growth mechanism of NHCT analyzed via advanced characterization revealed that the unique growth processes tuned a demarcating surface layer between inner (hydrophilic) and outer (hydrophobic) layers. The screening and recognition ability of NHCT were determined for two specific dipeptides (WW and RR) possessing great discrepancies in hydrophilicity and angiotensin converting enzyme inhibitory (ACE-I) activity. NHCT realized high adsorption capacity (1.57 mmol/g) and selectivity (∼1274) for hydrophilic dipeptide RR (low ACE-I activity) from the mixture of RR/WW. As a result, ACE-I activity for residual solution were enhanced about 4.1 times as compared to original solution from natural silkworm pupae protein hydrolysate. Awarding to these results and its facile and discerning ability, NHCT can be envisioned to be of great value for the separation of small functional peptides from a natural edible source.

Quantification of Multifunctional Dipeptide YA from Oyster Hydrolysate for Quality Control and Efficacy Evaluation

YA is an angiotensin-I-converting enzyme- (ACE-) inhibitory peptide from oyster hydrolysate with antihypertensive activity. Its antioxidant and anti-inflammatory activity were investigated in this study. YA can dose-dependently quench DPPH and ABTS radical and inhibit lipopolysaccharide-induced nitric oxide in RAW 264.7 cells. YA is a multifunctional peptide and was selected as an indicator for quality control and efficacy evaluation of oyster hydrolysate. A practical HPLC/UV assay for YA quantification was developed and validated. It was proved to be accurate and reliable, according to parameters such as specificity, linearity, precision, and accuracy. The quantity results of YA showed that the stage of enzymatic hydrolysis was a critical control point for quality control; the efficacy of oyster hydrolysate can be enhanced after digested in the gastrointestinal tract due to the release of YA by brush border peptidases. Therefore, YA from oyster hydrolysate is a potential bioactive ingredient for functional foods to combat hypertension.

Roasted Barley Extract (Mugi-cha) Containing Cyclo(d-Phe-l-Pro) Prevents Lowering of the Cutaneous Blood Flow and Skin Temperature under Air Conditioning: A Randomized, Double-Blind, Placebo-Controlled, Crossover Study

Roasted barley extract (RBE), also known as mugi-cha, is a well-known healthy non-caffeinated beverage, and its health functionality has been widely reported. Our previous clinical study showed that RBE affects the cutaneous blood flow and skin temperature after cold-water immersion and that cyclo(d-Phe-l-Pro) is responsible for its effect. In this study, we investigated whether cyclo(d-Phe-l-Pro)-containing RBE prevents the decrease in the cutaneous blood flow and skin temperature. Subjects remained in the air-conditioned room while ingesting RBE or a placebo. We measured the cutaneous blood flow and skin temperature. We evaluated the effect of RBE administration by two-way repeated measures analysis of variance. A total of 15 subjects were enrolled. The change in cutaneous blood flow in the RBE and placebo groups was -0.79 ± 0.38 and -2.03 ± 0.35 mL min^-1 100 g^-1, respectively ( p value of 0.041). The change in the skin temperature in the RBE and placebo groups was -1.85 ± 0.35 and -3.02 ± 0.30 °C, respectively ( p value of <0.001). We also did subclass analysis with cold-feeling subjects. For the seven subjects who had cold sensation, the change in the cutaneous blood flow in the RBE and placebo groups was -0.48 ± 0.58 and -2.56 ± 0.48 mL min^-1 100 g^-1, respectively ( p value of 0.008). The change in the skin temperature in the RBE and placebo groups was -1.46 ± 0.74 and -2.89 ± 0.39 °C, respectively ( p value of 0.009). Thus, RBE containing cyclo(d-Phe-l-Pro) prevents the decrease in the cutaneous blood flow and skin temperature under air conditioning.

Comparison of Kinetic Characteristics of Amino Acid-Based and Dipeptide-Based Peritoneal Dialysis Solutions

A mixture of dipeptides (DP) has been proposed as alternatives (to glucose and amino acids, (AA)) osmotic agent in peritoneal dialysis (PD) solutions. DP based solutions may have metabolic and nutritional advantages compared to AA based solutions, as some sources of AA (such as tyrosine) are poorly soluble in water. In a previous study, we compared the kinetic characteristics of DP and AA based solutions; however, the amount of AA differed substantially. The aim of the present study was to compare solutions with almost equal amounts of AA.

Methods

The following solutions were used: (1) amino acid (AA) solution containing leucine, valine, lysine, isoleucine, threonine, phenylalanine and histidine (tyrosine was omitted because of its poor solubility), (2) dipeptide (DP) solution containing leucyl-valine, lysyl-isoleucine, threonyl-phenylalanine and histidyl-tyrosine. Sixteen Sprague-Dawley rats were divided in two groups and were subjected to intraperitoneal injection of either 25 mL of AA (n=8) or DP solution. Dialysate and blood samples were taken frequently postinfusion for measurement of AA and DP concentrations as well as AA from DP.

Results

Kinetic models were developed for estimation of diffusive mass transport coefficient between peritoneal cavity and blood (KBD), DP hydrolysis rate coefficient (KH) and AA clearance in the body (KC). Calculations showed that KH is about ten times lower than KBD. Thus, hydrolysis rate in peritoneal cavity is much lower than the diffusive transport rate of DP. KBD for AA appeared to be similar to KBD for dipeptides. KC was much higher than KBD for AA. This finding explains the rapid clearance of amino acids from blood. Nevertheless, the AA-based solution resulted in much higher peak concentrations of AA in blood after 120 min of the dwell than AA concentrations achieved following the use of the DP-based solution.

Conclusions

Peritoneal transport characteristics of AA and DP were similar; however their kinetics in blood differs substantially. The DP solution resulted in a less pronounced increase in AA concentrations in blood, suggesting that DP solution could provide AA in a more physiological way.

RAFP-Pred: Robust Prediction of Antifreeze Proteins Using Localized Analysis of n-Peptide Compositions

In extreme cold weather, living organisms produce Antifreeze Proteins (AFPs) to counter the otherwise lethal intracellular formation of ice. Structures and sequences of various AFPs exhibit a high degree of heterogeneity, consequently the prediction of the AFPs is considered to be a challenging task. In this research, we propose to handle this arduous manifold learning task using the notion of localized processing. In particular, an AFP sequence is segmented into two sub-segments each of which is analyzed for amino acid and di-peptide compositions. We propose to use only the most significant features using the concept of information gain (IG) followed by a random forest classification approach. The proposed RAFP-Pred achieved an excellent performance on a number of standard datasets. We report a high Youden's index (sensitivity+specificity-1) value of 0.75 on the standard independent test data set outperforming the AFP-PseAAC, AFP_PSSM, AFP-Pred, and iAFP by a margin of 0.05, 0.06, 0.14, and 0.68, respectively. The verification rate on the UniProKB dataset is found to be 83.19 percent which is substantially superior to the 57.18 percent reported for the iAFP method.

Quantification of hydroxycinnamic derivatives in wines by UHPLC-MRM-MS

A UHPLC-MS/MS method was developed for the quantification of the main compounds involved in oxidation reactions occurring in white musts and wines such as hydroxycinnamic acids, their glutathione and cysteinylglycine adducts (GRP, GRP2, 5-(S-glutathionyl)-trans-caftaric acid, 2-(S-cysteinylglycyl)-trans-caftaric acid, and 2-(S-glutathionyl)-trans-caffeic acid), and reduced and oxidized glutathione (GSH, GSSG) in wine. Since oxidation is the main concern in white wine-making, directly affecting its quality, the developed method was then applied in a series of white wines made with different pre-fermentation treatments to limit oxidation at must stage. The glucose esters and/or glucosides of hydroxycinnamic acids were quantified as glucogallin equivalent. The developed method led to an overall improvement in the limits of detection (LODs) and quantification (LOQs) for all the compounds studied in comparison to other methods such as high-performance liquid chromatography with fluorescence detection (HPLC-FLD) or diode array UV detection (HPLC-DAD). LOD values ranged from 0.0002 to 0.0140 mg/L and LOQs from 0.0005 to 0.0470 mg/L. The recoveries ranged between 80 and 110% in wines, and the relative standard deviation (RSD) for precision intra- and inter-day was below 15%. The accuracy and intra- and inter-day precision met the acceptance criteria of the AOAC international norms. As far as we know, this study is the first report of quantification of GRP, 2-(S-cysteinylglycyl)-trans-caftaric acid, and 2-(S-glutathionyl)-trans-caffeic acid using these non-commercially available compounds as external standards. Those compounds represent a significant proportion of hydroxycinnamic acid derivatives in wines. The methodology described is suitable for the analysis of hydroxycinnamic derivatives in wines.

Piriformospora indica Stimulates Root Metabolism of Arabidopsis thaliana

Piriformospora indica is a root-colonizing fungus, which interacts with a variety of plants including Arabidopsis thaliana. This interaction has been considered as mutualistic leading to growth promotion of the host. So far, only indolic glucosinolates and phytohormones have been identified as key players. In a comprehensive non-targeted metabolite profiling study, we analyzed Arabidopsis thaliana’s roots, root exudates, and leaves of inoculated and non-inoculated plants by ultra performance liquid chromatography/electrospray ionization quadrupole-time-of-flight mass spectrometry (UPLC/(ESI)-QTOFMS) and gas chromatography/electron ionization quadrupole mass spectrometry (GC/EI-QMS), and identified further biomarkers. Among them, the concentration of nucleosides, dipeptides, oligolignols, and glucosinolate degradation products was affected in the exudates. In the root profiles, nearly all metabolite levels increased upon co-cultivation, like carbohydrates, organic acids, amino acids, glucosinolates, oligolignols, and flavonoids. In the leaf profiles, we detected by far less significant changes. We only observed an increased concentration of organic acids, carbohydrates, ascorbate, glucosinolates and hydroxycinnamic acids, and a decreased concentration of nitrogen-rich amino acids in inoculated plants. These findings contribute to the understanding of symbiotic interactions between plant roots and fungi of the order of Sebacinales and are a valid source for follow-up mechanistic studies, because these symbioses are particular and clearly different from interactions of roots with mycorrhizal fungi or dark septate endophytes

Electrospray ionization tandem mass spectrometric study of protonated and alkali- cationized α/ε-hybrid peptides: differentiation of a pair of dipeptide positional isomers

A new class of Boc-N-protected hybrid peptides derived from L- Ala and ε⁶-Caa (L-Ala = L-Alanine, Caa = C-linked carboamino acid derived from D-xylose) have been studied by positive ion electrospray ionization (ESI) ion-trap tandem mass spectrometry (MS/MS). MSⁿ spectra of protonated and alkali-cationized hybrid peptides produce characteristic fragmentation involving the peptide backbone, the tert-butyloxycarbonyl (Boc) group, and the side chain. The dipeptide positional isomers are differentiated by the collision-induced dissociation (CID) of the protonated and alkali-cationized peptides. The CID of [M + H]⁺ ion of Boc-NH-L-Ala-ε-Caa- OCH₃ (1) shows a prominent [M + H - C₄H₈]⁺ ion, which is totally absent for its positional isomer Boc-NH-ε-Caa-L-Ala-OCH₃ (6), which instead shows significant loss of t-butanol. The formation of the [M + Cat - C₄H₈]⁺ ion is totally absent and [M + Cat - Boc + H]⁺ is prominent in the CID of the [M + Cat]⁺ ion of Boc-NH-L-Ala-ε-Caa- OCH₃ (1), whereas the former is highly abundant and the latter is of low abundance for its positional isomer Boc-NH-ε-Caa-L-Ala-OCH₃ (6). It is observed that 'b' ions are abundant when oxazolone structures are formed through a five-membered cyclic transition state in tetra-, penta-, and hexapeptides and the cyclization process for larger 'b' ions led to an insignificant abundance. However, the significant 'b' ion is formed in ε,α-dipeptide, which may have a seven-membered substituted 2-oxoazepanium ion structure. The MSⁿ spectra of [M + Cat - Boc + H]⁺ ions of these peptides are found to be significantly different to those of [M + H - Boc + H]⁺ ions. The CID spectra of [M + Cat - Boc + H]⁺ ions of peptide acids containing L-Ala at the C-terminus show an abundant N-terminal rearrangement ion, [bⁿ + 17 + Cat]⁺, which is absent for the peptide acids containing ε-Caa at the C-terminus. Thus, the results of these hybrid peptides provide sequencing information, the structure of the cyclic intermediate involved in the formation of the rearrangement ion, and distinguish a pair of dipeptide positional isomers.

Quantitative mass spectrometric analysis of dipeptides in protein hydrolysate by a TNBS derivatization-aided standard addition method

The aim of this study was to establish, through a standard addition method, a convenient quantification assay for dipeptides (GY, YG, SY, YS, and IY) in soybean hydrolysate using 2,4,6-trinitrobenzene sulfonate (TNBS) derivatization-aided LC-TOF-MS. Soybean hydrolysate samples (25.0 mg mL(-1)) spiked with target standards were subjected to TNBS derivatization. Under the optimal LC-MS conditions, five target dipeptides derivatized with TNBS were successfully detected. Examination of the standard addition curves, with a correlation coefficient of r(2) > 0.979, provided a reliable quantification of the target dipeptides, GY, YG, SY, YS, and IY, in soybean hydrolysate to be 424 ± 20, 184 ± 9, 2188 ± 199, 327 ± 16, and 2211 ± 133 μg g(-1) of hydrolysate, respectively. The proposed LC-MS assay is a reliable and convenient assay method, with no interference from matrix effects in hydrolysate, and with no requirement for the use of an isotope labeled internal standard.

Identification of chemical markers in Cordyceps sinensis by HPLC-MS/MS

Authentication and quality assessment of Cordyceps sinensis, a precious and pricey natural product that offers a variety of health benefits, is highly significant. To identify effective chemical markers, authentic C. sinensis was thoroughly screened by using HPLC-MS/MS. In addition to many previously reported ingredients, two glycosides, i.e., cyclo-Ala-Leu-rhamnose and Phe-o-glucose, were detected for the first time in this material. Six ingredients detected, including cordycepin, D-mannitol, Phe, Phe-o-glucose, cyclo-Gly-Pro, and cyclo-Ala-Leu-rhamnose, were selected as a collection of chemical markers. An HPLC-MS/MS method was developed to simultaneously quantify them with sensitivity and specificity. The method had limits of detection ranging from 0.008 μg mL(-1) for cordycepin to 0.75 μg mL(-1) for cyclo-Gly-Pro. Recovery was found between 96 and 103 % in all tests. To evaluate the effectiveness of the marker collection proposed, five authentic C. sinensis samples and five samples of its substitutes were analyzed. Cordycepin, D-mannitol, and Phe were found present in all samples. The contents ranged from 0.0076 to 0.029 % (w/w) for cordycepin, 0.33 to 18.9 % for mannitol, and 0.0013 to 0.642 % for Phe. Interestingly, the two glycosides, Phe-o-glucose and cyclo-Ala-Leu-rhamnose, were detected only in authentic C. sinensis samples. These results indicated that the proposed protocol based on HPLC-MS/MS quantification of the markers might have a great potential in authentication and quality assessment of C. sinensis. Graphical abstract Chemical markers of C. sinensis identified in this work.

[Chemical Constituents from Periplaneta americana]

OBJECTIVE

To study the chemical constituents in Periplaneta americana.

METHODS

The chemical constituents were separated and purified by chromatographic methods after solvent extraction and identified by spectroscopic analyses.

RESULTS

Ten compounds were isolated from Periplaneta americana and identified as following: 8-hydroxy-3,4-dihydroquinolin-2 (1H)-one (1), cyclo-( L-Phe-L-Pro) (2), cyclo-(Pro-Ile) (3), cyclo-(L-Pro-D-Leu) (4), brevianamide F (5), cyclo-(Ile-Ala) (6), cyclo-( L-Val-L-Pro) (7), cyclo-(L-Pro-L-Tyr) (8), cyclo-(Trp-Val)-dipeptide (9), and (-)-(1S, 3S)-1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (10).

CONCLUSION

Compounds 2 - 9 are isolated from Periplaneta americana for the first time.

The distribution of glutathione and homoglutathione in leaf, root and seed tissue of 73 species across the three sub-families of the Leguminosae

Homoglutathione (γ-glutamyl-cysteinyl-β-alanine) is a homologue of glutathione (γ-glutamyl-cysteinyl-glycine), which is a ubiquitous and indispensable tripeptide in eukaryotes with multi-facetted functions, many of which relate to cellular redox regulation. Homoglutathione is unique to the Leguminosae family, but studies of its occurrence have been restricted to the Papilionoideae subfamily, and almost exclusively to crop species. To determine whether the distribution of homoglutathione in the Leguminosae has a phylogenetic basis the occurrence of homoglutathione was investigated in the leaves, roots and seeds of 73 wild species of Leguminosae, representing 30 tribes across the Caesalpinioideae, Mimosoideae and Papilionoideae subfamilies. Homoglutathione was found only in the Papilionoideae, and was generally restricted to the 'Old World Clade'. It is proposed that homoglutathione may have arisen following a whole genome duplication event after the divergence of the Old World Clade. Homoglutathione is believed to fulfil the same functional roles as glutathione, but this study showed that homoglutathione and glutathione have different tissue-specific distribution patterns. Homoglutathione tended to occur more frequently in root tissue, and higher concentrations were found in leaves and roots, whereas glutathione tended to be present at the highest concentrations in seeds. This may reflect a distinct role for homoglutathione, particularly in roots, or an inability of homoglutathione to functionally replace glutathione in reproductive tissues. However, no relationships with environmental factors or nodulation were observed. Greater understanding of the factors that influence homoglutathione distribution may help to elucidate its unique function in some legume species.

Formation of a(1) ions directly from oxazolone b(2) ions: an energy-resolved and computational study

It is well-known that oxazolone b2 ions fragment extensively by elimination of CO to form a2 ions, which often fragment further to form a1 ions. Less well-known is that some oxazolone b2 ions may fragment directly to form a1 ions. The present study uses energy-resolved collision-induced dissociation experiments to explore the occurrence of the direct b2→a1 fragmentation reaction. The experimental results show that the direct b2→a1 reaction is generally observed when Gly is the C-terminal residue of the oxazolone. When the C-terminal residue is more complex, it is able to provide increased stability of the a2 product in the b2→a2 fragmentation pathway. Our computational studies of the relative critical reaction energies for the b2→a2 reaction compared with those for the b2→a1 reaction provide support that the critical reaction energies are similar for the two pathways when the C-terminal residue of the oxazolone is Gly. By contrast, when the nitrogen of the oxazolone ring in the b2 ion does not bear a hydrogen, as in the Ala-Sar and Tyr-Sar (Sar = N-methylglycine) oxazolone b2 ions, a1 ions are not formed but rather neutral imine elimination from the N-terminus of the b2 ion becomes a dominant fragmentation reaction. The M06-2X/6-31+G(d,p) density functional theory calculations are in general agreement with the experimental data for both types of reaction. In contrast, the B3LYP/6-31+G(d,p) model systematically underestimates the barriers of these SN2-like b2→a1 reaction. The difference between the two methods of barrier calculation are highly significant (P < 0.001) for the b2→a1 reaction, but only marginally significant (P = 0.05) for the b2→a2 reaction. The computations provide further evidence of the limitations of the B3LYP functional when describing SN2-like reactions.

Compatible validated spectrofluorimetric and spectrophotometric methods for determination of vildagliptin and saxagliptin by factorial design experiments

Simple, selective and reproducible spectrofluorimetric and spectrophotometric methods have been developed for the determination of vildagliptin and saxagliptin in bulk and their pharmaceutical dosage forms. The first proposed spectrofluorimetric method is based on the dansylation reaction of the amino group of vildagliptin with dansyl chloride to form a highly fluorescent product. The formed product was measured spectrofluorimetrically at 455 nm after excitation at 345 nm. Beer's law was obeyed in a concentration range of 100-600 μg ml(-1). The second proposed spectrophotometric method is based on the charge transfer complex of saxagliptin with tetrachloro-1,4-benzoquinone (p-chloranil). The formed charge transfer complex was measured spectrophotometrically at 530 nm. Beer's law was obeyed in a concentration range of 100-850 μg ml(-1). The third proposed spectrophotometric method is based on the condensation reaction of the primary amino group of saxagliptin with formaldehyde and acetyl acetone to form a yellow colored product known as Hantzsch reaction, measured at 342.5 nm. Beer's law was obeyed in a concentration range of 50-300 μg ml(-1). All the variables were studied to optimize the reactions' conditions using factorial design. The developed methods were validated and proved to be specific and accurate for quality control of vildagliptin and saxagliptin in their pharmaceutical dosage forms.

Cuprizone-induced demyelination and demyelination-associated inflammation result in different proton magnetic resonance metabolite spectra

Conventional MRI is frequently used during the diagnosis of multiple sclerosis but provides only little additional pathological information. Proton MRS ((1) H-MRS), however, provides biochemical information on the lesion pathology by visualization of a spectrum of metabolites. In this study we aimed to better understand the changes in metabolite concentrations following demyelination of the white matter. Therefore, we used the cuprizone model, a well-established mouse model to mimic type III human multiple sclerosis demyelinating lesions. First, we identified CX3 CL1/CX3 CR1 signaling as a major regulator of microglial activity in the cuprizone mouse model. Compared with control groups (heterozygous CX3 CR1(+/-) C57BL/6 mice and wild type CX3 CR1(+/+) C57BL/6 mice), microgliosis, astrogliosis, oligodendrocyte cell death and demyelination were shown to be highly reduced or absent in CX3 CR1(-/-) C57BL/6 mice. Second, we show that (1) H-MRS metabolite spectra are different when comparing cuprizone-treated CX3 CR1(-/-) mice showing mild demyelination with cuprizone-treated CX3 CR1(+/+) mice showing severe demyelination and demyelination-associated inflammation. Following cuprizone treatment, CX3 CR1(+/+) mice show a decrease in the Glu, tCho and tNAA concentrations as well as an increased Tau concentration. In contrast, following cuprizone treatment CX3 CR1(-/-) mice only showed a decrease in tCho and tNAA concentrations. Therefore, (1) H-MRS might possibly allow us to discriminate demyelination from demyelination-associated inflammation via changes in Tau and Glu concentration. In addition, the observed decrease in tCho concentration in cuprizone-induced demyelinating lesions should be further explored as a possible diagnostic tool for the early identification of human MS type III lesions.

Differential laser-induced perturbation Raman spectroscopy: a comparison with Raman spectroscopy for analysis and classification of amino acids and dipeptides

Differential-laser induced perturbation spectroscopy (DLIPS) is a new spectral analysis technique for classification and identification, with key potential applications for analysis of complex biomolecular systems. DLIPS takes advantage of the complex ultraviolet (UV) laser–material interactions based on difference spectroscopy by coupling low intensity UV laser perturbation with a traditional spectroscopy probe. Here, we quantify the DLIPS performance using a Raman scattering probe in classification of basic constituents of collagenous tissues, namely, the amino acids glycine, L-proline, and L-alanine, and the dipeptides glycine–glycine, glycine–alanine and glycine–proline and compare the performance to a traditional Raman spectroscopy probe via several multivariate analyses. We find that the DLIPS approach yields an ~40% improvement in discrimination among these tissue building blocks. The effects of the 193-nm perturbation laser are further examined by assessing the photodestruction of targeted material molecular bonds. The DLIPS method with a Raman probe holds promise for future tissue diagnosis, either as a stand-alone technique or as part of an orthogonal biosensing scheme.

Analyzing a dipeptide library to identify human dipeptidyl peptidase IV inhibitor

Human dipeptidyl peptidase IV (hDPPIV) inhibitors provide an effective strategy for the treatment of type 2 diabetes. Because certain peptides are known to act as hDPPIV inhibitors, a dataset of possible peptides with their inhibition intensities will facilitate the development of functional food for type 2 diabetes. In this study, we examined a total of 337 dipeptides with respect to their hDPPIV inhibitory effects. Amino acid residues at N-termini dominated their inhibition intensities. Particularly highly inhibitory dipeptides discovered included the following novel dipeptides: Thr-His, Asn-His, Val-Leu, Met-Leu, and Met-Met. Using our dataset, prime candidates contributing to the hDPPIV inhibitory effect of soy protein hydrolyzates were successfully identified. Possible dietary proteins potentially able to produce particularly highly hDPPIV inhibitory peptides are also discussed on the basis of the dataset.

ALLocator: an interactive web platform for the analysis of metabolomic LC-ESI-MS datasets, enabling semi-automated, user-revised compound annotation and mass isotopomer ratio analysis

Adduct formation, fragmentation events and matrix effects impose special challenges to the identification and quantitation of metabolites in LC-ESI-MS datasets. An important step in compound identification is the deconvolution of mass signals. During this processing step, peaks representing adducts, fragments, and isotopologues of the same analyte are allocated to a distinct group, in order to separate peaks from coeluting compounds. From these peak groups, neutral masses and pseudo spectra are derived and used for metabolite identification via mass decomposition and database matching. Quantitation of metabolites is hampered by matrix effects and nonlinear responses in LC-ESI-MS measurements. A common approach to correct for these effects is the addition of a U-¹³C-labeled internal standard and the calculation of mass isotopomer ratios for each metabolite. Here we present a new web-platform for the analysis of LC-ESI-MS experiments. ALLocator covers the workflow from raw data processing to metabolite identification and mass isotopomer ratio analysis. The integrated processing pipeline for spectra deconvolution “ALLocatorSD” generates pseudo spectra and automatically identifies peaks emerging from the U-¹³C-labeled internal standard. Information from the latter improves mass decomposition and annotation of neutral losses. ALLocator provides an interactive and dynamic interface to explore and enhance the results in depth. Pseudo spectra of identified metabolites can be stored in user- and method-specific reference lists that can be applied on succeeding datasets. The potential of the software is exemplified in an experiment, in which abundance fold-changes of metabolites of the l-arginine biosynthesis in C. glutamicum type strain ATCC 13032 and l-arginine producing strain ATCC 21831 are compared. Furthermore, the capability for detection and annotation of uncommon large neutral losses is shown by the identification of (γ-)glutamyl dipeptides in the same strains. ALLocator is available online at: https://allocator.cebitec.uni-bielefeld.de. A login is required, but freely available.

Measurement of regional variation of GABA in the human brain by optimized point-resolved spectroscopy at 7 T in vivo

The (1)H resonances of γ-aminobutyric acid (GABA) in the human brain in vivo are extensively overlapped with the neighboring abundant resonances of other metabolites and remain indiscernible in short-TE MRS at 7 T. Here we report that the GABA resonance at 2.28 ppm can be fully resolved by means of echo time optimization of a point-resolved spectroscopy (PRESS) scheme. Following numerical simulations and phantom validation, the subecho times of PRESS were optimized at (TE, TE2) = (31, 61) ms for detection of GABA, glutamate (Glu), glutamine (Gln), and glutathione (GSH). The in vivo feasibility of the method was tested in several brain regions in nine healthy subjects. Spectra were acquired from the medial prefrontal, left frontal, medial occipital, and left occipital brain and analyzed with LCModel. Following the gray and white matter (GM and WM) segmentation of T1 -weighted images, linear regression of metabolite estimates was performed against the fractional GM contents. The GABA concentration was estimated to be about seven times higher in GM than in WM. GABA was overall higher in frontal than in occipital brain. Glu was about twice as high in GM as in WM in both frontal and occipital brain. Gln was significantly different between frontal GM and WM while being similar between occipital GM and WM. GSH did not show significant dependence on tissue content. The signals from N-acetylaspartylglutamate were clearly resolved, giving the concentration more than 10 times higher in WM than in GM. Our data indicate that the PRESS TE = 92 ms method provides an effective means for measuring GABA and several challenging J-coupled spin metabolites in human brain at 7 T.

Simultaneous determination of glutathione, cysteine, homocysteine, and cysteinylglycine in biological fluids by ion-pairing high-performance liquid chromatography coupled with precolumn derivatization

Biologically active low-molecular-mass thiols, mainly including glutathione (GSH), cysteine (Cys), homocysteine (Hcy), and cysteinylglycine (Cys-Gly), are important physiological components in biological fluids, and their analytical methods have gained continuous attention over recent years. We developed and validated a novel HPLC method for the quantification of GSH, Cys, Hcy, and Cys-Gly in human plasma, urine, and saliva using 4-chloro-3,5-dinitrobenzotrifluoride as the derivatization reagent. Analyses were linear from 0.15 to 500 μM with the coefficient regression range of 0.9987-0.9994. Detection limits ranged from 0.04 to 0.08 μM (S/N=3). The developed method was applied to quantification of four thiols in human biological fluids collected from five donors with the concentration range of 2.50-124.25 μM, 0-72.81 μM, and 0-4.25 μM for plasma, urine, and saliva, respectively. The present method seemed to be an attractive choice for the determination of thiols in plasma, urine, and saliva.

Cryogenically cooled octupole ion trap for spectroscopy of biomolecular ions

We present here the design of a linear octupole ion trap, suitable for collisional cryogenic cooling and spectroscopy of large ions. The performance of this trap has been assessed using ultraviolet (UV) photofragmentation spectroscopy of protonated dipeptides. At the trap temperature of 6.1 K, the vibrational temperature of the ions reaches 9.1 K, although their estimated translational temperature is ~150 K. This observation suggests that, despite the significant translational heating by radio-frequency electrical field, vibrational cooling of heavy ions in the octupole is at least as efficient as in the 22-pole ion traps previously used in our laboratory. In contrast to the 22-pole traps, excellent radial confinement of ions in the octupole makes it convenient for laser spectroscopy and boosts the dissociation yield of the stored ions to 30%. Overlap of the entire ion cloud by the laser beam in the octupole also allows for efficient UV depletion spectroscopy of ion-He clusters. The measured electronic spectra of the dipeptides and the clusters differ drastically, complicating a use of UV tagging spectroscopy for structural determination of large species.

Identification, characterization, and quantification of an anti-pyridoxine factor from flaxseed using ultrahigh-performance liquid chromatography-mass spectrometry

In the present study, the anti-pyridoxine compounds linatine (1-[(n-γ-L-glutamyl)amino]-D-proline) and 1-amino-D-proline (1ADP) were quantified following extraction from defatted flaxseed using aqueous isopropanol as a solvent, with extraction variables including time, temperature, and the solid/solvent ratio. Both linatine and 1ADP were identified, characterized, and quantified via UPLC/ESI-MS using authentic standards. To optimize the extraction conditions for these anti-pyridoxine compounds, a response surface methodology was applied using a second-order polynomial to describe the experimental data. The predicted model for the optimal extraction was significant (P < 0.05) with a R(2) of 0.82. A varietal analysis showed that the amount of anti-pyridoxine present in flaxseed ranged from 177 to 437 μg 1ADPE/g of whole seed. The current study establishes the content of specific anti-pyridoxine factors in flaxseed and positions the data for use in subsequent risk assessment modeling.

Identification of pyroglutamyl peptides in Japanese rice wine (sake): presence of hepatoprotective pyroGlu-Leu

Japanese rice wine, sake, is made from steamed rice, water, and lactic acid by "multiple parallel fermentation" with mold (Aspergillus oryzae) and yeast (Saccharomyces cerevisiae). Nineteen pyroglutamyl peptides were identified in commercially available sake. Among them, pyroGlu-Leu and pyroGlu-Gln were the major constituents. PyroGlu-Leu has been demonstrated to attenuate hepatitis and colitis in animal models. Commercial products (n = 5) contained pyroGlu-Leu at concentrations ranging from 40 to 60 μM (10-15 mg/L). The pyroGlu-Leu content in sake mash increased during the fermentation processes. However, no pyroGlu-Leu was produced by yeast inoculated into preheated mash. Furthermore, addition of (13)C-Leu to the mash did not increase the ratio of pyroGlu-(13)C-Leu to pyroGlu-(12)C-Leu. On the other hand, digestion of steamed rice with A. oryzae proteases increased the pyroGlu-Leu content. These results indicate that pyroGlu-Leu in sake is produced from rice proteins by digestion with A. oryzae proteases.

Determination of neotame in non-alcoholic beverage by capillary zone electrophoresis

BACKGROUND

Neotame (NEO) is a new artificial sweetener approved as a food additive in many countries. The present method for the determination of NEO in various foodstuffs is high-performance liquid chromatography (HPLC). There are no reports on the determination of NEO in foods by capillary zone electrophoresis (CZE). Therefore a simple and rapid method to determine NEO is desired for quality control.

RESULTS

A CZE method combined with solid phase extraction was developed for the determination of NEO in non-alcoholic beverage. The optimum separation conditions obtained were 20 mmol L(-1) sodium borate buffer, pH 8, 25 kV applied voltage, 5 s hydrodynamic injection at 30 mbar and ultraviolet detection at 191 nm. The calibration curve showed good linearity (R(2) = 1.000) in the range 0.5-100 µg mL(-1) , and the limit of detection was 0.118 µg mL(-1) . The method was successfully applied to the determination of NEO in two kinds of beverage with migration time less than 5 min, relative standard deviation (n = 3) less than 2% and recoveries ranging from 90 to 95%.

CONCLUSION

The proposed CZE method has the advantages of shorter analysis time and lower cost compared with HPLC, indicating that it may be a good alternative to the HPLC method.

Identification of antioxidants from sequence information using naïve Bayes

Antioxidant proteins are substances that protect cells from the damage caused by free radicals. Accurate identification of new antioxidant proteins is important in understanding their roles in delaying aging. Therefore, it is highly desirable to develop computational methods to identify antioxidant proteins. In this study, a Naïve Bayes-based method was proposed to predict antioxidant proteins using amino acid compositions and dipeptide compositions. In order to remove redundant information, a novel feature selection technique was employed to single out optimized features. In the jackknife test, the proposed method achieved an accuracy of 66.88% for the discrimination between antioxidant and nonantioxidant proteins, which is superior to that of other state-of-the-art classifiers. These results suggest that the proposed method could be an effective and promising high-throughput method for antioxidant protein identification.

Capillary electrophoresis-mass spectrometry for Peptide analysis: target-based approaches and proteomics/peptidomics strategies

In this chapter, the potential of capillary electrophoresis-mass spectrometry (CE-MS) for peptide analysis is demonstrated by the presentation of two different strategies typically followed in analysis of these biomolecules by CE-MS. The first one is a target-based approach and it is used to detect a toxic oligopeptide in a complex matrix. Namely, CE-MS using an ion trap MS analyzer is applied to detect and quantify γ-glutamyl-S-ethenyl-cysteine (GEC) bioactive dipeptide in a legume plant. The second one is a shotgun-like methodology used for proteomic analysis. Particularly, CE-MS using a time-of-flight MS analyzer is employed to investigate the substantial equivalence between a genetically modified (GM) variety of soybean and its conventional isogenic counterpart. These generic methods have broad applications for the analysis of peptides in a large variety of matrices, including applications in the area of proteomics and peptidomics.

Characterization of brevetoxin metabolism in Karenia brevis bloom-exposed clams (Mercenaria sp.) by LC-MS/MS

Brevetoxin metabolites were identified and characterized in the hard clam (Mercenaria sp.) after natural exposure to Karenia brevis blooms by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Principal brevetoxins BTX-1 and BTX-2 produced by K. brevis were not detectable in clams. Metabolites of these brevetoxins found in clams included products of oxidation, reduction, hydrolysis and amino acid/fatty acid conjugation. Of highest abundance were cysteine and taurine conjugates. We also found glutathione, glycine-cysteine, and γ-glutamyl-cysteine conjugates. A series of fatty acid derivatives of cysteine-brevetoxin conjugates were also identified.

[Simultaneous determination of aspartame and alitame in jellies and preserved fruits by HPLC]

OBJECTIVE

To establish a determination method for aspartame and alitame in jellies and preserved fruits.

METHODS

Aspartame and alitame in jellies were extracted with 80% methanol at 70 degrees C. Preserved fruits were homogenized with water and then were extracted with 50% methanol. A chromatographic column Zorbax SB-C18 was used; the mobile phase was methanol/water (40 + 60, volume ratio), and a diode array detector was used for the detection at wavelength 200 nm.

RESULTS

The limits of quantification of aspartame and alitame were both 8 mg/kg for jellies and both 20 mg/kg for preserved fruits; the calibration curves were linear in the range of tested concentration. The correlation coefficients were better than 0.9996. The average recovery rates were in the range of 98.1% -101.2%, the relative standard deviations were 2.21% - 4.10%.

CONCLUSION

The method is simple, practical, accurate, reliable and successful in the determination of aspartame and alitame in jellies and preserved fruits from various brands on markets.

Discovery of salt taste enhancing arginyl dipeptides in protein digests and fermented fish sauces by means of a sensomics approach

As enzymatic digests of fish proteins were recently reported to enhance salt taste, the fish protein protamine was digested by chymotrypsin and trypsin and subsequently screened for candidate salt taste modulating (STM) peptides. To achieve this, first, a two-step sensory assay was developed and demonstrated to be a rather suitable tool for the detection of salt taste enhancers and the "quantitation" of their salt taste enhancing activity on the basis of isointensities with reference solutions. By means of activity-guided fractionation using ultrafiltration, gel permeation chromatography, and hydrophilic liquid interaction chromatography in combination with the sensory assay for STM activity assessment, a series of arginyl dipeptides, with RP, RA, AR, RG, RS, RV, VR, and RM being the most active, as well as l-arginine were found as salt taste enhancing molecules in fish protamine digests. For the first time, HPLC-MS/MS analysis on a PFP and a HILIC stationary phase, respectively, enabled the quantitative analysis of the arginyl peptides in a series of commercial and laboratory-made protein hydrolysates as well as fermented fish sauces.

Identification and quantitation of 3-S-cysteinylglycinehexan-1-ol (Cysgly-3-MH) in Sauvignon blanc grape juice by HPLC-MS/MS

Precursors to varietal wine thiols are a key area of grape and wine research. Several such precursors, in the form of odorless conjugates, have been closely studied in recent years. A new conjugate has now been identified as 3-S-cysteinylglycinehexan-1-ol (Cysgly-3-MH), being the dipeptide intermediate between cysteine and glutathione precursors of tropical thiol 3-mercaptohexan-1-ol (3-MH). Authentic Cysgly-3-MH was produced via enzymatic transformation of the glutathione conjugate and used to verify the presence of both diastereomers of Cysgly-3-MH in Sauvignon blanc juice extracts. Cysgly-3-MH was added into our HPLC-MS/MS precursor method, and the validated method was used to quantify this new analyte in a selection of Sauvignon blanc juice extracts. Cysgly-3-MH was found in the highest concentrations (10-28.5 μg/L combined diastereomer total) in extracts from berries that had been machine-harvested and transported for 800 km in 12 h. This dipeptide conjugate was much less abundant than the glutathione and cysteine conjugates in the samples studied. On the basis of the results, the new cysteinylglycine conjugate of 3-MH seemingly has a short existence as an intermediate precursor, which may explain why it has not been identified as a natural juice component until now.

Identification of arginine residues in peptides by 2D-IR echo spectroscopy

The CN stretching vibrations of the guanidyl group in the arginine dipeptide side chain are examined by two-dimensional infrared spectroscopy. In D(2)O, the spectra display two distinct diagonal peaks. These nearly degenerate modes undergo ultrafast energy transfer. The energy-transfer rate was determined directly from the 2D-IR spectra to be 1/2.1 ps(-1). The cross peaks in 2D-IR arising from the energy transfer provide a definitive identification of arginine in larger proteins. An example of arginine in the transmembrane protein M2, found in influenza viruses, is given.

Immunomodulatory effects of secondary metabolites from thermophilic Anoxybacillus kamchatkensis XA-1 on carp, Cyprinus carpio

A bacterial strain with putative immunomodulatory properties was isolated from Xi'an hot springs in China. Comparison of 16S rRNA gene revealed a 97% similarity between the tested strain (designated XA-1) and Anoxybacillus kamchatkensis. Two compounds isolated from the secondary metabolites of XA-1 were identified by spectral data (infrared, nuclear magnetic resonance and mass spectrometry) as: (1) cyclo (Gly-L-Pro) and (2) cyclo (L-Ala-4-hydroxyl-L-Pro). Two cyclic dipeptides showed stimulatory properties towards a range of parameters when a dose of 20mg kg(-1) body weight was intraperitoneally injected in naive common carp, Cyprinus carpio. Innate immune parameters (serum SOD, lysozyme and bactericidal activity, and phagocytic activity by peripheral blood leucocytes) along with the expression of two immune-related genes (IL-1β and iNOS) in blood were examined after 7, 14, 21, and 28 days of injection. In the absence of infection, immunomodulators should ideally not affect normal physiology and immunity of the host; possible negative outcomes of activated immune responses in the naive state are discussed. Protection by two bacterial dipeptides was assessed in an intraperitoneal injection challenge trial with live Aeromonas hydrophila. Both compounds reduced mortality, with the highest survival rate observed in the group that received compound 2 (80%) followed by the group that received compound 1 (65%) while control group scored the worse (15%). Elucidation of the involved protective mechanisms in carp requires future studies.

1H-HRMAS NMR study of smoked Atlantic salmon (Salmo salar)

High-resolution magic angle spinning (HRMAS) NMR spectroscopic data of smoked Atlantic salmon (Salmo salar) were fully assigned by combination of one- and two-dimensional-HRMAS experiments. Complete representative spectra, obtained after few minutes of analysis time, revealed a large number of minor and major compounds in the sample. The methodology is limited by the low sensitivity of NMR, and therefore HRMAS only enables the determination of the most relevant components. These were fatty acids (FAs), carbohydrates, nucleoside derivatives, osmolytes, amino acids, dipeptides and organic acids. For the first time, spectra were resolved sufficiently to allow semiquantitative determination in intact muscle of the highly polyunsaturated FA 22:6 omega-3. Additionally, the feasibility of (1)H-HRMAS NMR metabolite profiling was tested to identify some bioactive compounds during storage. This profiling was carried out by the non-destructive and direct analysis (i.e. without requiring sample preparation and multiple step procedures) of intact salmon muscle. The proposed procedure can be applied to a large number of samples with high throughput due to the short time of analysis and quick evaluation of the data.

[Chemical constituents of Gekko swinhonis]

OBJECTIVE

To study the chemical constituents of Gekko swinhonis.

METHOD

The compounds were isolated and purified by several column chromatographic methods with silica gel, ODS, Sephadex LH-20 and preparative HPLC, Their structures were identified by physicochemical properties and spectral data.

RESULT

Thirteen compounds were isolated and elucidated as cyclo-(Pro-Leu) (1), cyclo-(Ala-Pro) (2),cyclo-(Gly-Pro) (3),cyclo-(Ala-Val) (4),6-amino-9-beta-D-ribofuranosyl-9H-purine (5), uridine (6), thymidine (7),hypoxanthine-9-beta-D-ribofuranosid (8),L-phenylalanine (9),5alpha-cholest-3,6-dione (10),cholesterol (11), 1-O-hexadecanolenin (12),octadecanoic acid (13),respectively.

CONCLUSION

All compounds were isolated from G. swinhonis for the first time.

Over-expression of bacterial gamma-glutamylcysteine synthetase (GSH1) in plastids affects photosynthesis, growth and sulphur metabolism in poplar (Populus tremula x Populus alba) dependent on the resulting gamma-glutamylcysteine and glutathione levels

We compared three transgenic poplar lines over-expressing the bacterial gamma-glutamylcysteine synthetase (GSH1) targeted to plastids. Lines Lggs6 and Lggs12 have two copies, while line Lggs20 has three copies of the transgene. The three lines differ in their expression levels of the transgene and in the accumulation of gamma-glutamylcysteine (gamma-EC) and glutathione (GSH) in leaves, roots and phloem exudates. The lowest transgene expression level was observed in line Lggs6 which showed an increased growth, an enhanced rate of photosynthesis and a decreased excitation pressure (1-qP). The latter typically represents a lower reduction state of the plastoquinone pool, and thereby facilitates electron flow along the electron transport chain. Line Lggs12 showed the highest transgene expression level, highest gamma-EC accumulation in leaves and highest GSH enrichment in phloem exudates and roots. This line also exhibited a reduced growth, and after a prolonged growth of 4.5 months, symptoms of leaf injury. Decreased maximum quantum yield (F(v)/F(m)) indicated down-regulation of photosystem II reaction centre (PSII RC), which correlates with decreased PSII RC protein D1 (PsbA) and diminished light-harvesting complex (Lhcb1). Potential effects of changes in chloroplastic and cytosolic GSH contents on photosynthesis, growth and the whole-plant sulphur nutrition are discussed for each line.

Effects of dietary protein level in the early fattening period on free amino acids and dipeptides in the blood and Longissimus thoracis muscle in Japanese Black steers

The effects of crude protein (CP) concentration in feed using soybean meal as its source in the early fattening period on the levels of free amino acids (FAAs) and dipeptides in the blood, and the levels in the M. longissimus thoracis after slaughter were studied in Japanese Black steers. Sixteen steers were divided into four groups and given feed with a CP content of 12, 14, 16, or 18% of dry matter (DM) from 10 to 20 months old, and they were fed with the same level of CP (13.5-13.9% of DM) until slaughter at 30 months of age. There was no significant difference in the weight gain, carcass weight or marbling score between the groups. Concerning the serum FAA and dipeptide contents at 20 months of age, the alanine, tyrosine and tryptophan levels decreased, while the carnosine (Car) level increased, with increases in the CP level in the feed. Although there were no significant differences in the FAA contents of the Longissimus thoracis muscle between the groups, the Car content decreased with increases in the feed protein level.

Detection of in vivo matrix metalloproteinase activity using microdialysis sampling and liquid chromatography/mass spectrometry

Matrix metalloproteinases (MMPs) are a family of endoproteases that break down extracellular matrix and whose upregulation contributes to several diseases. A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed to quantify MMP-1 and MMP-9 substrates and their N-terminal peptide products in samples obtained from implanted microdialysis sampling probes. In vitro studies with purified human MMP-1 and MMP-9 were used to optimize the assay and determine the effectiveness of the local delivery of a broad-spectrum MMP inhibitor, GM 6001. Localized delivery of GM 6001 at 10 microM was sufficient to completely inhibit product formation in vitro. In vivo studies in male Sprague-Dawley rats were performed with microdialysis probes implanted into the subcutaneous tissue. Directly after microdialysis probe implantation, infusions of the MMP-1 and MMP-9 substrates (50 microM each) resulted in recovered product concentrations of approximately 2 microM. During a 50 microM GM 6001 coinfusion with the substrates, a 30% and 25% reduction in product formation for the MMP-1 and MMP-9 substrates was obtained, respectively. Blank dialysates were negative for enzymatic activity that could cleave the MMP substrates. This method allowed for the activity of different MMPs surrounding the microdialysis probe to be observed during in vivo sampling.

The fate of amino acids during simulated meteoritic impact

Delivery of prebiotic molecules, such as amino acids and peptides, in meteoritic/micrometeoritic materials to early Earth during the first 500 million years is considered to be one of the main processes by which the building blocks of life arrived on Earth. In this context, we present a study in which the effects of impact shock on amino acids and a peptide in artificial meteorites composed of saponite clay were investigated. The samples were subjected to pressures ranging from 12-28.9 GPa, which simulated impact velocities of 2.4-5.8 km/s for typical silicate-silicate impacts on Earth. Volatilization was determined by weight loss measurement, and the amino acid and peptide response was analyzed by gas chromatography-mass spectrometry. For all compounds, degradation increased with peak pressure. At the highest shock pressures, amino acids with an alkyl side chain were more resistant than those with functional side chains. The peptide cleaved into its two primary amino acids. Some chiral amino acids experienced partial racemization during the course of the experiment. Our data indicate that impact shock may act as a selective filter to the delivery of extraterrestrial amino acids via carbonaceous chondrites.

Sensory-directed identification of beta-alanyl dipeptides as contributors to the thick-sour and white-meaty orosensation induced by chicken broth

Sensory-directed fractionation of a double-boiled chicken broth using ultrafiltration, gel permeation chromatography, PFPP-HPLC, and HILIC combined with analytical sensory techniques led to the identification of beta-alanyl-N-methyl-l-histidine, beta-alanyl-l-histidine, and the previously unreported beta-alanylglycine as the key contributors to the thick-sour orosensation and typical white-meaty character of chicken broth. Quantitative analysis, followed by taste recombination and omission experiments, revealed for the first time that, when present together with l-glutamic acid and sodium and/or potassium ions, subthreshold concentrations of these beta-alanyl peptides enhance the typical thick-sour orosensation and white-meaty character known for poultry meat, although these taste-modulatory peptides exhibited only a faint sour and slightly astringent intrinsic taste when tasted individually.

Bio-detection of dipeptides by the ZrO2/PVA/Cyt.c multilayer film

The adsorption mechanism of dipeptides namely Gly-Glu, Asp-Glu with protein layer was successfully examined on cytochrome c (Cyt.c) surface probing by fluorescent dye molecule. Molecularly thin Cyt.c layer was immobilized on poly(vinyl alcohol) (PVA) coated zirconium oxide (ZrO2) gel films by electrostatic interaction. Denaturation of Cyt.c was minimized on sol-gel derived ZrO2-gel film by PVA. The conformation of immobilized protein was verified by FTIR-ATR measurements. The fluorescent dye molecule was easily bound on the Cyt.c layer. The dye adsorbed protein thin film was soaked in two different dipeptides solution with various concentrations. The adsorption of dipeptides on Cyt.c thin film and consequent desorption of fluorescent dye from Cyt.c layer in dipeptide solutions was monitored by UV-vis absorption, fluorescence spectroscopy and quartz crystal microbalance method. The ion exchange mechanism on protein surface between fluorescent dye and dipeptides is thought to be responsible for dye desorption and formation of relatively strong electrostatic bonding between dipeptides with protein. The adsorption behavior curve of dipeptides was analyzed by Hill equation. The number of functional group together with size of dipeptides play an important role for different adsorption parameters obtained from this model.

Kokumi-active glutamyl peptides in cheeses and their biogeneration by Penicillium roquefortii

Recently, a group of gamma-glutamyl dipeptides, but not the alpha-glutamyl dipeptides, were found to induce the attractive kokumi flavor of matured Gouda cheese. In the present investigation, the spatial distribution of alpha- and gamma-glutamyl dipeptides in Gouda cheese wheels and the concentration of these peptides in other cheese types were determined by means of HPLC-MS/MS. Among all cheeses investigated, by far the highest gamma-glutamyl peptide concentration (3590 mumol/kg) was found for Blue Shropshire, a blue-veined cheese. To check whether the gamma-glutamyl transferase (GGT) from Penicillium roquefortii is involved in gamma-glutamyl peptide production in this cheese, the GGT activity was measured and gamma-glutamyl peptides were analyzed in liquid cultures of mold isolated from Blue Shropshire as well as single P. roquefortiii strains incubated with the gamma-glutamyl donor l-glutamine and the candidate substrates l-glutamic acid, l-histidine, l-leucine, and l-methionine. Being well in line with the GGT activity found in Blue Shropshire, P. roquefortii was found for the first time to produce and secrete gamma-glutamyl peptides. Among the amino acids tested, l-methionine was found as a preferred gamma-glutamyl acceptor; for example, gamma-Glu-Met was produced in yields of about 50 mmol/mol and [(2)H(3)]-gamma-Glu-Met was obtained when [(2)H(3)]-l-methionine was used as substrate amino acid.

A series of kokumi peptides impart the long-lasting mouthfulness of matured Gouda cheese

Comparative sensory analysis revealed that a 44-week-matured Gouda cheese (GC44) exhibited a much more pronounced mouthfulness and long-lasting taste complexity when compared to a young Gouda cheese ripened for only 4 weeks (GC4). To identify the molecules underlying that so-called kokumi sensation, a sensomics approach was applied on the water-soluble extract (WSE44) of GC44 by combining gel permeation chromatography (GPC) with analytical sensory tools. HPLC-MS/MS experiments on GPC fractions inducing a kokumi sensation when tasted in an aqueous biomimetic taste recombinant solution (rWSE44) enabled the identification of 8 alpha-L-glutamyl and 10 gamma-L-glutamyl dipeptides as candidate kokumi-enhancing molecules. Among those, only the gamma-L-glutamyl dipeptides were found to impart an enhanced kokumi sensation to the matured cheese, whereas none of the alpha-glutamyl peptides were found to be active. Among the gamma-L-glutamyl peptides, the candidates gamma-Glu-Glu, gamma-Glu-Gly, gamma-Glu-Gln, gamma-Glu-Met, gamma-Glu-Leu, and gamma-Glu-His, present in GC44 in concentrations between 4.11 and 17.66 micromol/kg, were identified for the first time as the key kokumi molecules enhancing mouthfulness and complex taste continuity of the matured cheese.

Conformational studies on cyclic dipeptides

An analysis of 11 crystal structures of cyclic dipeptides so far reported in the literature is made, with main reference to the internal parameters of these molecules. Preferred conformations of the side chains of cyclic dipeptides with different alpha-amino acid residues have been studied by classical energy calculations. The possible conformations of the DKP ring are also studied. The significance of the non-bonded interaction in deciding the pathway for conformational change has also been investigated. The agreement between theoretical results and experimental observations is quite good, both with respect to the conformation of these molecules as well as the enthalpy difference as estimated from n.m.r. studies between different conformers.

Characterization of structural variations in the peptidoglycan of vancomycin-susceptible Enterococcus faecium: understanding glycopeptide-antibiotic binding sites using mass spectrometry

Enterococcus faecium, an opportunistic pathogen that causes a significant number of hospital-acquired infections each year, presents a serious clinical challenge because an increasing number of infections are resistant to the so-called antibiotic of last resort, vancomycin. Vancomycin and other new glycopeptide derivatives target the bacterial cell wall, thereby perturbing its biosynthesis. To help determine the modes of action of glycopeptide antibiotics, we have developed a bottom-up mass spectrometry approach complemented by solid-state nuclear magnetic resonance (NMR) to elucidate important structural characteristics of vancomycin-susceptible E. faecium peptidoglycan. Using accurate-mass measurements and integrating ion-current chromatographic peaks of digested peptidoglycan, we identified individual muropeptide species and approximated the relative amount of each. Even though the organism investigated is susceptible to vancomycin, only 3% of the digested peptidoglycan has the well-known D-Ala-D-Ala vancomycin-binding site. The data are consistent with a previously proposed template model of cell-wall biosynthesis where D-Ala-D-Ala stems that are not cross-linked are cleaved in mature peptidoglycan. Additionally, our mass-spectrometry approach allowed differentiation and quantification of muropeptide species seen as unresolved chromatographic peaks. Our method provides an estimate of the extent of muropeptides containing O-acetylation, amidation, hydroxylation, and the number of species forming cyclic imides. The varieties of muropeptides on which the modifications are detected suggest that significant processing occurs in mature peptidoglycan where several enzymes are active in editing cell-wall structure.