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PubMed2006

Methylglyoxal is an intermediate in the biosynthesis of 6-deoxy-5-ketofructose-1-phosphate: a precursor for aromatic amino acid biosynthesis in Methanocaldococcus jannaschii.

A biosynthetic pathway is proposed for creating 6-deoxy-5-ketofructose-1-phosphate (DKFP), a precursor sugar for aromatic amino acid biosynthesis in Methanocaldococcus jannaschii. First, two possible routes were investigated to determine if a modified, established biosynthetic pathway could be responsible for generating 6-deoxyhexoses in M. jannaschii. Both the nucleoside diphosphate mannose pathway and a pathway involving nucleoside diphosphate derivatives of fructose-1-P, fructose-2-P, or fructose-1,6-bisP were tested and eliminated. The established pathways did not produce the expected intermediates nor did the anticipated enzymes have the predicted enzymatic activities. Because neither anticipated pathway could produce DKFP, M. jannaschii glucose-6-P metabolism was studied in detail to establish exactly how glucose-6-P is converted into DKFP. This detailed analysis showed that methylglyoxal and a fructose-1-P- or fructose-1,6-bisP-derived dihydroxyacetone-P fragment are key intermediates in DKFP production. Glucose-6-P readily converts to fructose-6-P, which in turn converts to fructose-1,6-bisP. Fructose-6-P and fructose-1,6-bisP convert into glyceraldehyde-3-P (Ga-P-3), which converts into methylglyoxal by a 2,3-elimination of phosphate. The MJ1585-derived enzyme catalyzes the condensation of methylglyoxal with a dihydroxyacetone-P fragment, which is derived from fructose-1-P and/or fructose-1,6-bisP, generating DKFP. The elimination of phosphate from Ga-P-3 proceeds by both enzymatic and chemical routes in cell extracts, producing sufficient concentrations of methylglyoxal to support the reaction. This work is the first report of methylglyoxal functioning in central metabolism.

Fructosephosphates↗
PubMed2006

Site-selective modifications of arginine residues in human hemoglobin induced by methylglyoxal.

Methylglyoxal (MG) is an important glycating agent produced under physiological conditions. MG could react with DNA and proteins to generate advanced glycation end products. Human hemoglobin, the most abundant protein in blood cells, has not been systematically investigated as the target protein for methylglyoxal modification. Here we examined carefully, by using HPLC coupled with tandem mass spectrometry (LC-MS/MS), the covalent modifications of human hemoglobin induced by methylglyoxal. Our results revealed that hemoglobin could be modified by methylglyoxal, and the major form of modification was found to be the hydroimidazolone derivative of arginine residues. In addition, Arg-92 and Arg-141 in the alpha chain as well as Arg-40 and Arg-104 in the beta chain were modified, whereas two other arginine residues, that is, Arg-31 in the alpha chain and Arg-30 in the beta chain, were not modified. Semiquantitative measurement for adduct formation, together with the analysis of the X-ray structure of hemoglobin, showed that the extents of arginine modification were highly correlated with the solvent accessibilities of these residues. The facile formation of hydroimidazolone derivatives of arginine residues in hemoglobin by methylglyoxal at physiologically relevant concentrations suggested that this type of modification might occur in vivo. The unambiguous determination of the sites and extents of methylglyoxal modifications of arginines in hemoglobin provided a basis for understanding the implications of these modifications and for employing this type of hemoglobin modification as molecular biomarkers for clinical applications.

Amino Acid Sequence↗
PubMed2003

OH radical-initiated reaction of 3-hexene-2,5-dione: formation of methylglyoxal.

3-Hexene-2,5-dione [CH3C(O)CH=CHC(O)CH3] and other unsaturated 1,4-dicarbonyls are formed from the atmospheric photooxidations of aromatic hydrocarbons. We have reinvestigated the formation of methylglyoxal from the gas-phase reaction of OH radicals with 3-hexene-2,5-dione in the presence of NO at room temperature and atmospheric pressure of air using in situ Fourier transform infrared spectroscopy. No evidence for the formation of methylglyoxal was obtained, with the IR spectra showing that methylglyoxal is, at most, a minor reaction product with a molar formation yield of <10% (and more likely <1%). This confirms our earlier study (Tuazon et al. Environ. Sci. Technol. 1985, 19, 265) and suggests that the CH3C(O)CH(OH)CHO and CH3C(O)CH(OH)CH(ONO2)C(O)CH3 observed by Bethel et al. (Environ. Sci. Technol. 2001, 35, 4477) are the major first-generation reaction products.

Air Pollutants↗
PubMed2005

Gas-phase chemistry of (alpha-terpineol with ozone and OH radical: rate constants and products.

A bimolecular rate constant, kOH+alpha-terpineol, of (1.9 +/- 0.5) x 10(-10) cm3 molecule(-1) s(-1) was measured using gas chromatography/mass spectrometry and the relative rate technique for the reaction of the hydroxyl radical (OH) with alpha-terpineol (1-methyl-4-isopropyl-1-cyclohexen-8-ol) at (297 +/- 3) K and 1 atm total pressure. Additionally, a bimolecular rate constant, kO3+alpha-terpineol, of (3.0 +/- 0.2) x 10(-16) cm3 molecule(-1) s(-1) was measured by monitoring the first order decrease in ozone concentration as a function of excess alpha-terpineol. To better understand alpha-terpineol's gas-phase transformation in the indoor environment, the products of the alpha-terpineol + OH and alpha-terpineol + 03 reactions were also investigated. The positively identified alpha-terpineol/OH reaction products were acetone, ethanedial (glyoxal, HC(=O)C(=O)H), and 2-oxopropanal (methyl glyoxal, CH3C(=O)C(=O)H). The positively identified alpha-terpineol/O3 reaction product was 2-oxopropanal (methyl glyoxal, CH3C(=O)C(=O)H). The use of derivatizing agents O-(2,3,4,5,6-pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible alpha-terpineol/OH and alpha-terpineol/O3 reaction mechanisms based on previously published volatile organic compound/ OH and volatile organic compound/O3 gas-phase reaction mechanisms.

Air Pollutants↗
PubMed2006

Outside-in trimming of humic substances during ozonation in a membrane contactor.

This paper addresses the change of molecular size distribution of humic substances (HS) during ozonation in a membrane contactor. It focuses on the characterization and identification of some small ozonation products. The membrane contactor setup allows very precise control of ozone transfer into the solution as well as precise sampling of the products in time. The molecular size distribution was followed by gel permeation chromatography (GPC). Characterization and identification of small ozonation products was performed by membrane nanofiltration and high-performance liquid chromatography (HPLC). Measurements on molecular size distribution indicate that during the ozonation process the size of the HS molecules decreases slowly and only small highly oxidated compounds are being split off the larger molecules. Pyruvic acid, formic acid, methylglyoxal, and acetaldehyde could be identified by substantial peaks. Glyoxilic acid and glyoxal were identified to a lesser extent. This suggests that HS molecules consist of a relatively stable backbone network structure and that the HS molecule degrades according to an outside-in trimming mechanism.

Acetaldehyde↗
PubMed2025

Decoding Arginine Dimethylation Isomers via pH-Tuned Reactivity with Methylglyoxal: A Chemical Approach for Functional Proteomics.

Arginine dimethylation, encompassing asymmetric and symmetric configurations, represents a fundamental post-translational modification. Despite sharing identical chemical formulas, the two arginine dimethylation isomers exhibit different or even opposite biological effects. Therefore, it is necessary to determine their specific structure before conducting a further biological investigation. However, current methods for arginine dimethylation analysis face great challenges in efficient isomer differentiation, preventing the functional investigation of arginine dimethylation. To overcome this obstacle, herein, we introduce a novel chemical strategy leveraging pH-tuned reactivity with methylglyoxal (MGO) to decode these dimethylation isomers. By utilizing molecular dynamics simulation analysis, we revealed the different chemical reactivities of asymmetrically and symmetrically dimethylated arginine when reacted with MGO at different pH conditions. This property enabled the development of a pH-tuned chemical strategy by combining the MGO reaction with boronate affinity enrichment to simultaneously enrich and differentiate the dimethylation isomers. This strategy can effectively distinguish dimethylated arginine isomers in complex cell samples, and the good feasibility of this strategy was verified by orthogonal validation with the neutral loss. Of the obtained data set, this strategy identified sDMA at R112 of SNRPN, which is confirmed to be modified by PRMT5. Further functional analysis reveals its crucial role in maintaining protein stability and in regulating spliceosome assembly. Overall, by transforming the inherent pH sensitivity of MGO reactions into a powerful analytical tool, our work establishes the first chemical platform for functional proteomic dissection of arginine dimethylation isomers, which paves the way for further regulating mechanism investigations of protein methylation.

Pyruvaldehyde↗
PubMed2001

N(delta)-(5-hydroxy-4,6-dimethylpyrimidine-2-yl)-l-ornithine, a novel methylglyoxal-arginine modification in beer.

N(delta)-(5-Hydroxy-4,6-dimethylpyrimidine-2-yl)-L-ornithine, or Argpyrimidine, was identified and quantified in beer by high-performance liquid chromatography (HPLC) and coupled gas chromatography-mass spectrometry (HRGC-MS). This novel fluorescent arginine Maillard modification represents the first amino acid modification reported in beer retaining the full backbone of the original amino acid. Two mechanisms of formation could be verified: the major pathway via methylglyoxal and the minor pathway via 5-deoxypentoses. Argpyrimidine concentrations, determined in 35 lager-type beer varieties, reached up to 27 nmol/L and could be positively correlated to beer color and wort content. Within this context, 5-deoxy-D-ribose was identified as a novel intermediate of the Maillard reaction of maltose by HRGC-MS and independent synthesis.

Acetone↗
PubMed2002

Qualitative determination of specific protein glycation products by matrix-assisted laser desorption/ionization mass spectrometry Peptide mapping.

The nonenzymatic reaction between reducing sugars and proteins, known as the Maillard reaction, has received increased recognition from nutritional science and medical research. The development of new analytical techniques for the detection of protein-bound Maillard products is therefore crucial. In this study, we applied peptide mapping by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to investigate the formation of structurally specific Maillard products on glycated lysozyme (AGE-lysozyme), produced upon incubation with D-glucose. In parallel, we synthesized N(epsilon)-(carboxymethyl)lysine-modified lysozyme (CML-lysozyme) and N(epsilon)-(carboxyethyl)lysine-modified lysozyme, two well-described glycation products, as model substances. 3-Deoxyglucosone-modified lysozyme and methylglyoxal-modified lysozyme were prepared as examples of glycation products incubated with dicarbonyl compounds. We were able to detect specific modifications on AGE-lysozyme, which were assigned to CML, imidazolone A, and the Amadori product.

Deoxyglucose↗
PubMed2003

Improved superoxide-generating system suitable for the assessment of the superoxide-scavenging ability of aqueous extracts of food constituents using ultraweak chemiluminescence.

In the interest of developing a simple and rapid ultraweak chemiluminescence assay for assessing the superoxide (O(2)(-))-scavenging activities of various aqueous extracts of food constituents, a specific and stable O(2)(-)-generating system was sought. Reported herein is the obtainment for the first time of a specific and stable O(2)(-)-generating system consisting of methylglyoxal (MG), a reactive 2-oxo aldehyde and arginine, which has been shown to produce much steadier lucigenin-based chemiluminesence (LBCL) than the conventional xanthine/xanthine oxidase system running in parallel and monitoring by an ultraweak chemiluminescence analyzer. Upon mixing of MG and arginine in a phosphate-buffered saline solution, pH 7.4, steady, time-dependent increments of LBCL can be visually observed. The plateau of LBCL can be reached in approximately 10 min and retained in a steadily stable state thereafter without fluctuation for the next 15 min. The lucigenin-based LBCL generation was shown to be specific since it could be effectively inhibited by active bovine SOD, but not by heat-inactivated enzyme or catalase. Conversely, the xanthine/xanthine oxidase system can merely produce a LBCL peak rapidly but decay instantaneously. To illustrate the application of the proposed method for assessing the O(2)(-)-scavenging ability of various food extracts, namely, Prunus mume (A), Lilum lancifolium (B), Creataegus pinnatifida (C), Tremella fuciformis (D), Fortunella margarita (E), and Scutellaria baicalensis (F), we used the following protocol: 12 min after monitoring of LBCL, 1 mg/mL of each of the test compounds was added to the assay system and various degrees of sudden drop of LBCL values were observed, indicating differences in O(2)(-)-scavenging abilities exerted by these food extracts that can be visually compared. Consequently, the percentages of inhibition of LBCL versus the concentrations of a test compound can be constructed. It follows that the concentration needed to inhibit 50% of LBCL (IC(50)) of a test compound can be extrapolated from the curve. Using this approach, we were able to obtain the IC(50) values of various compounds to be tested and the order of inhibitory efficiency of the above-mentioned food extracts was ranked, being A > B > C > D > E > F, respectively.

Acridines↗
PubMed2002

Possible mechanism for involvement of cysteine in aroma production in wine.

Under conditions close to those of wine, that is, low pH, aqueous medium, and low temperatures, this work describes N-(2-sulfanylethyl)-2-oxopropanamide (1), a new intermediate in the formation of 2-acetylthiazole from methylglyoxal and cysteine. 1 was characterized by MS, derivatization MS, and (1)H and (13)C NMR and was synthesized from 2-sulfanylethanamine and ethyl pyruvate. A formation pathway for 2-acetylthiazole from methylglyoxal and cysteine is proposed, in which 1 is a new intermediate in Maillard-type reactions in systems under mild conditions.

Cysteine↗
PubMed2004

Determination of methylglyoxal in ruminal fluid by high-performance liquid chromatography using fluorometric detection.

There is no reported method for the quantification of methylglyoxal in ruminal fluid. The method reported here is based on the conversion of methylglyoxal to 6-methylpterin, followed by quantification of the resulting pteridinic compound by fluormetric detection using liquid chromatography. Ruminal fluid was collected and preserved with 1 M HCl at -20 degrees C. Cation exchange prior to derivatization was used to eliminate possible interfering peaks. The detection limit of 0.125 microg/mL was calculated. The recoveries were >80%, and the coefficients of variation were <15%. This method has proven to be rugged and accurate for the detection of methylglyoxal concentration in ruminal fluid collected from cows fed diets deficient in degradable intake protein as a marker. Methylglyoxal is produced by ruminal bacteria in response to low nitrogen levels in the rumen. The ruminal methylglyoxal concentration has the potential to be a useful marker to assess ruminal nitrogen status to aid in more accurate diet formulation.

Animals↗
PubMed2006

Epicatechin carbonyl-trapping reactions in aqueous maillard systems: Identification and structural elucidation.

Recently, our group reported via labeling experiments that epicatechin in Maillard reaction aqueous glucose-glycine model systems formed adduct reaction products with C2, C3, and C4 sugar fragments. In the current study, we investigated the identity of the sugar fragment precursors responsible for adduct generation by directly comparing the liquid chromatography-mass spectrometry properties of these reported epicatechin (EC)-sugar fragments adducts with those generated from reactions consisting of only EC and well-known Maillard-generated glucose fragments (i.e., glyoxal, glycolaldehyde, methylglyoxal, glyceraldehyde, etc.). The structural properties of an EC-methylglyoxal adduct reaction product were also analyzed by NMR. The most likely precursors for the C2, C3, and C4 sugar moiety of the EC-sugar fragment adducts were identified as glyoxal, hydroxyacetone, and erythrose, respectively. 1H NMR analysis of the EC-methylglyoxal indicated that the analyte underwent rapid conformational/constitutional exchange. Using cold temperature (-25 degrees C) two-dimensional NMR analyses (heteronuclear multiple bond coherence, heteronuclear multiple quantum coherence, and 1H-(1)H correlation spectroscopy), the structure of one of the isomers was reported to consist of a covalent linkage between the C1 position of the methylglyoxal and either the C6 or the C8 position of the EC A ring, presumably generated by hydroxyalkylation and aromatic substitution reactions.

Carbon↗
PubMed2006

Investigations on the promoting effect of ammonium hydrogencarbonate on the formation of acrylamide in model systems.

NH4HCO3 is known to promote acrylamide formation in sweet bakery products. This effect was investigated with respect to sugar fragmentation and formation of acrylamide from asparagine and sugar fragments in model systems under mild conditions. The presence of NH4HCO3 led to increases in acrylamide and alpha-dicarbonyls from glucose and fructose, respectively. As compared to glucose or fructose, sugar fragments such as glyoxal, hydroxyethanal, and glyceraldehyde formed much higher amounts of acrylamide in reaction with asparagine. The enhancing effect of NH4HCO3 is explained by (1) the action of NH3 as base in the retro-aldol reactions leading to sugar fragments, (2) facilitated retro-aldol-type reactions of imines in their protonated forms leading to sugar fragments, and (3) oxidation of the enaminols whereby glyoxal and other reactive sugar fragments are formed. These alpha-dicarbonyl and alpha-hydroxy carbonyl compounds may play a key role in acrylamide formation, especially under mild conditions.

Acrylamide↗
PubMed1975

Growth inhibitory properties of aromatic alpha-ketoaldehydes toward bacteria and yeast. Comparison of inhibition and glyoxalase I activity.

The alpha-ketoaldehydes methylglyoxal and substituted phenylglyoxals are similar in their abilities to inhibit the growth of Escherichia coli and yeast. When logarithmically growing cells are added to media containing 0.3-1 mM alpha-ketoaldehyde, growth stops for several hours, after which normal growth resumes. The period of growth inhibition does not appear to show any correlation with the ability of glyoxalase I to detoxify these alpha-ketoaldehydes. E. coli and yeast glyoxalase I show markedly different substrate specificities. For example, although both enzymes show broad specificity for both aliphatic and aromatic alpha-ketoaldehydes, 2,4,6-trimethylphenylglyoxal is a substrate for the E. coli enzyme but not for the yeast enzyme. Nevertheless, this alpha-ketoaldehyde inhibits the growth of both E. coli and yeast, similar to the other alpha-ketoaldehydes. Enzymes other than glyoxalase I must play a major role in the metabolism of these alpha-ketoaldehydes during the period of growth inhibition.

Aldehydes↗