Oxidation Of Methylglyoxal Research Articles

Oxidation of methylglyoxal to CO2 by cultured A-10 vascular smooth muscle cells

The uptake of [2-14C]-methylglyoxal, a glucose metabolite, and its possible oxidation to carbon dioxide (CO2) were investigated in cultured A-10 vascular smooth muscle cells. A-10 cells bound and took up [2-14C]-methylglyoxal in a concentration-dependent manner. The uptake of [2-14C]-methylglyoxal was a rapid process, it was already detectable in the cells after 5 min of incubation, reaching a plateau by 30 min of incubation. The presence of fetal bovine serum in the incubation medium hampered the uptake of [2-14C]-methylglyoxal, suggesting an interaction between proteins and the α-oxoaldehyde. After an incubation longer than 60 min a loss of cell bound radioacticvity was detected which, as it turned out in separate experiments, was mainly due to CO2 formation from the α-oxoaldehyde. These results suggest that the generation of CO2 from methylglyoxal may be substantial in cultured cells and that methylglyoxal may contribute to the energy production below intracellular concentrations under a certain limit. In A-10 cells, this limit proved to be 300 μM, since above this concentration of methylglyoxal cell damage occurred.

Chemical insights, explicit chemistry, and yields of secondary organic aerosol from OH radical oxidation of methylglyoxal and glyoxal in the aqueous phase

Abstract. Atmospherically abundant, volatile water-soluble organic compounds formed through gas-phase chemistry (e.g., glyoxal (C2), methylglyoxal (C3), and acetic acid) have great potential to form secondary organic aerosol (SOA) via aqueous chemistry in clouds, fogs, and wet aerosols. This paper (1) provides chemical insights into aqueous-phase OH-radical-initiated reactions leading to SOA formation from methylglyoxal and (2) uses this and a previously published glyoxal mechanism (Lim et al., 2010) to provide SOA yields for use in chemical transport models. Detailed reaction mechanisms including peroxy radical chemistry and a full kinetic model for aqueous photochemistry of acetic acid and methylglyoxal are developed and validated by comparing simulations with the experimental results from previous studies (Tan et al., 2010, 2012). This new methylglyoxal model is then combined with the previous glyoxal model (Lim et al., 2010), and is used to simulate the profiles of products and to estimate SOA yields. At cloud-relevant concentrations (~ 10−6 − ~ 10−3 M; Munger et al., 1995) of glyoxal and methylglyoxal, the major photooxidation products are oxalic acid and pyruvic acid, and simulated SOA yields (by mass) are ~ 120% for glyoxal and ~ 80% for methylglyoxal. During droplet evaporation oligomerization of unreacted methylglyoxal/glyoxal that did not undergo aqueous photooxidation could enhance yields. In wet aerosols, where total dissolved organics are present at much higher concentrations (~ 10 M), the major oxidation products are oligomers formed via organic radical–radical reactions, and simulated SOA yields (by mass) are ~ 90% for both glyoxal and methylglyoxal. Non-radical reactions (e.g., with ammonium) could enhance yields.

Modelling multiphase chemistry in deliquescent aerosols and clouds using CAPRAM3.0i

Modelling studies were performed with the multiphase mechanism RACM-MIM2ext/CAPRAM 3.0i to investigate the tropospheric multiphase chemistry in deliquesced particles and non-precipitating clouds using the SPACCIM model framework. Simulations using a non-permanent cloud scenario were carried out for two different environmental conditions focusing on the multiphase chemistry of oxidants and other linked chemical subsystems. Model results were analysed by time-resolved reaction flux analyses allowing advanced interpretations. The model shows significant effects of multiphase chemical interactions on the tropospheric budget of gas-phase oxidants and organic compounds. In-cloud gas-phase OH radical concentration reductions of about 90 % and 75 % were modelled for urban and remote conditions, respectively. The reduced in-cloud gas-phase oxidation budget increases the tropospheric residence time of organic trace gases by up to about 30 %. Aqueous-phase oxidations of methylglyoxal and 1,4-butenedial were identified as important OH radical sinks under polluted conditions. The model revealed that the organic C3 and C4 chemistry contributes with about 38 %/48 % and 8 %/9 % considerably to the urban and remote cloud / aqueous particle OH sinks. Furthermore, the simulations clearly implicate the potential role of deliquescent particles to operate as a reactive chemical medium due to an efficient TMI/HOx,y chemical processing including e.g. an effective in-situ formation of OH radicals. Considerable chemical differences between deliquescent particles and cloud droplets, e.g. a circa 2 times more efficient daytime iron processing in the urban deliquescent particles, were identified. The in-cloud oxidation of methylglyoxal and its oxidation products is identified as efficient sink for NO3 radicals in the aqueous phase.

Mechanisms leading to oligomers and SOA through aqueous photooxidation: insights from OH radical oxidation of acetic acid and methylglyoxal

Abstract. Previous experiments have demonstrated that the aqueous OH radical oxidation of methylglyoxal produces low volatility products including pyruvate, oxalate and oligomers. These products are found predominantly in the particle phase in the atmosphere, suggesting that methylglyoxal is a precursor of secondary organic aerosol (SOA). Acetic acid plays a central role in the aqueous oxidation of methylglyoxal and it is a ubiquitous product of gas phase photochemistry, making it a potential "aqueous" SOA precursor in its own right. However, the fate of acetic acid upon aqueous-phase oxidation is not well understood. In this research, acetic acid (20 μM–10 mM) was oxidized by OH radicals, and pyruvic acid and methylglyoxal experimental samples were analyzed using new analytical methods, in order to better understand the formation of SOA from acetic acid and methylglyoxal. Glyoxylic, glycolic, and oxalic acids formed from acetic acid and OH radicals. In contrast to the aqueous OH radical oxidation of methylglyoxal, the aqueous OH radical oxidation of acetic acid did not produce succinic acid and oligomers. This suggests that the methylgloxal-derived oligomers do not form through the acid catalyzed esterification pathway proposed previously. Using results from these experiments, radical mechanisms responsible for oligomer formation from methylglyoxal oxidation in clouds and wet aerosols are proposed. The importance of acetic acid/acetate as an SOA precursor is also discussed. We hypothesize that this and similar chemistry is central to the daytime formation of oligomers in wet aerosols.

Size distributions and chemical characterization of water‐soluble organic aerosols over the western North Pacific in summer

Size‐segregated aerosol samples were collected over the western North Pacific in summer 2008 to investigate marine biological contribution to organic aerosols. The samples were analyzed for organic carbon (OC), water‐soluble organic carbon (WSOC), and water‐soluble organic compounds including diacids (C2–C9), ω‐oxocarboxylic acids, and α‐dicarbonyls as well as methanesulfonic acid (MSA). The average concentrations of OC and oxalic acid (C2) were approximately two to three times larger in marine biologically more influenced aerosols, defined by the concentrations of MSA and azelaic acid (C9), than in less influenced aerosols. WSOC, which showed a statistically significant correlation with MSA, accounted for 15–21% of total mass of the components determined in the submicrometer range of biologically more influenced aerosols. These values are comparable to those of water‐insoluble organic carbon (WIOC) (∼14–23%), suggesting that organic aerosols in this region are enriched in secondary organic aerosols (SOA) linked to oceanic biological activity. In these aerosols, substantial fractions of C2–C4 diacids were found in the submicrometer size range. Positive correlations of oxalic acid with C3–C5 diacids and glyoxylic acid suggest that secondary production of oxalic acid occurs possibly in the aqueous aerosol phase via the oxidation of longer‐chain diacids and glyoxylic acid in the oceanic region with higher biological productivity. We found similar concentration levels and size distributions of methylglyoxal between the two types of aerosols, suggesting that formation of oxalic acid via the oxidation of methylglyoxal from marine isoprene is insignificant in the study region.

SOA from methylglyoxal in clouds and wet aerosols: Measurement and prediction of key products

Abstract Aqueous OH radical oxidation of methylglyoxal in clouds and wet aerosols is a potentially important global and regional source of secondary organic aerosol (SOA). We quantify organic acid products of the aqueous reaction of methylglyoxal (30–3000 μM) and OH radical (approx. 4 × 10 −12 M), model their formation in the reaction vessel and investigate how the starting concentrations of precursors and the presence of acidic sulfate (0–840 μM) affect product formation. Predicted products were observed. The predicted temporal evolution of oxalic acid, pyruvic acid and total organic carbon matched observations at cloud relevant concentrations (30 μM), validating this methylglyoxal cloud chemistry, which is currently being implemented in some atmospheric models of SOA formation. The addition of sulfuric acid at cloud relevant concentrations had little effect on oxalic acid yields. At higher concentrations (3000 μM), predictions deviate from observations. Larger carboxylic acids (≥C 4 ) and other high molecular weight products become increasingly important as concentration increases, suggesting that small carboxylic acids are the major products in clouds while larger carboxylic acids and oligomers are important products in wet aerosols.

Methylglyoxal as substrate and inhibitor of human aldehyde dehydrogenase: Comparison of kinetic properties among the three isozymes

Methylglyoxal was demonstrated to be a substrate for the isozymes E1, E2 and E3 of human aldehyde dehydrogenase. Pyruvate was the product from the oxidation of methylglyoxal by the three isozymes. At pH 7.4 and 25 oC, the major and minor components of the E3 isozyme catalyzed the reaction with V max of 1.1 and 0.8 μmol NADH min −1 mg −1 protein, respectively, compared to 0.067 and 0.060 μmol NADH min −1 mg −1 protein for the E1 and E2 isozymes, respectively. The E2 isozyme had a K m for methylglyoxal of 8.6 μM, the lowest compared to 46 μM for E1 and 586 and 552 μM for the major and minor components of the E3 isozyme, respectively. Both components of the E3 isozyme showed substrate inhibition by methylglyoxal, with K i values of 2.0 mM for the major component and 12 mM for the minor component at pH 9.0. Substrate inhibition by methylglyoxal was not observed with the E1 and E2 isozymes. Methylglyoxal strongly inhibited the glycolaldehyde activity of the E1 and E2 isozymes. Mixed-type models of inhibition were employed as an approach to calculate the inhibition constants, 44 and 10.6 μM for E1 and E2 isozymes, respectively.

The UV‐visible absorption spectrum and photolysis quantum yields of methylglyoxal

Laboratory studies have been conducted to determine the rate and mechanism of methylglyoxal (MGLY, CH3COCHO) photolysis under tropospheric conditions. The UV/visible absorption cross sections of MGLY as a function of wavelength have been measured at three different temperatures, 248 K, 273 K, and 298 K. The absorption cross sections show only small variations (≤10%) over this temperature range. The results at 298 K are in agreement with the values published by Meller et al. (1991) and differ by almost a factor of 2 from earlier work published by Plum et al. (1983). The quantum yields and products of the photolysis are reported for various wavelength bands between 240 and 480 nm. The dominant pathway for photolysis at wavelengths relevant to the troposphere produces two radicals, CH3COCHO + hν → CH3CO + HCO. The measured absorption cross sections and quantum yields are used to determine a methylglyoxal lifetime for photolysis of (2.7±0.7) hours, for a solar zenith angle of 0–60°. The kinetics and mechanism for reaction of HO2 with methylglyoxal were also determined. Although this reaction is unimportant for the atmospheric oxidation of methylglyoxal, the results were used in the interpretation of the quantum yield experiments.

FTIR study of the Cl‐atom initiated oxidation of methylglyoxal

AbstractThe kinetics and mechanism of Cl‐atom initiated reactions of CH3C(O)CHO were studied using the FTIR detection method in the photolysis (λ < 300 nm) of Cl2CH3C(O)CHO mixtures in 700 torr of N2O2 diluent at 298 ± 2 K. The observed product distribution over the O2 pressure range from 0–700 torr, combined with relative rate measurements, provided evidence that: (1) the primary step is Cl + CH3C(O)CHO → HCl + CH3C(O)CO with a rate constant of (4.8 ± 1.1) × 10−11 cm3 molecule−1 s−1; and (2) the predominant fate of the primary radical CH3C(O)CO under atmospheric conditions is unimolecular dissociation to CH3C(O) radicals and CO, rather than O2‐addition to yield the corresponding carbonylperoxy radical CH3C(O)C(O)OO.

Glyoxal oxidase of Phanerochaete chrysosporium: its characterization and activation by lignin peroxidase.

Glyoxal oxidase (GLOX) is an extracellular H2O2-generating enzyme produced by ligninolytic cultures of Phanerochaete chrysosporium. The production, purification, and partial characterization of GLOX from agitated cultures are described here. High-oxygen levels are critical for GLOX production as for lignin peroxidase. GLOX purified by anion-exchange chromatography appears homogeneous by NaDod-SO4/PAGE (molecular mass = 68 kDa). However, analysis by isoelectric focusing indicates two major bands (pI 4.7 and 4.9) that stain as glycoproteins as well as for H2O2-producing activity in the presence of methylglyoxal. Purified GLOX shows a marked stimulation in activity when incubated with Cu2+; full activation takes more than 1 hr with 1 mM CuSO4 at pH 6. The steady-state kinetic parameters for the GLOX oxidation of methylglyoxal, glyceraldehyde, dihydroxyacetone, glycolaldehyde, acetaldehyde, glyoxal, glyoxylic acid, and formaldehyde, were determined by using a lignin peroxidase coupled-assay at pH 4.5. Of these substrates, the best is the extracellular metabolite methylglyoxal with a Km of 0.64 mM an apparent rate of catalysis, kcat, of 198 s1 under air-saturated conditions. The Km for oxygen is greater than the concentration of oxygen possible at ambient pressure--i.e., >1.3 mM at 25 degrees C. Importantly, oxygen-uptake experiments show that purified GLOX is inactive unless coupled to the peroxidase reaction. With this coupled reaction, for each mol of methylglyoxal, veratryl alcohol (a lignin peroxidase substrate), and oxygen consumed, 1 mol each of pyruvate and veratraldehyde is produced. The importance of these results is discussed in relation to the physiology of lignin biodegradation and possible extracellular regulatory mechanisms for the control of oxidase and peroxidase activities.

The oxidation of methylglyoxal by mammalian pyruvate dehydrogenase

Mammalian pyruvate dehydrogenase actively catalyzed the oxidation of methylglyoxal to acetyl-CoA. The reaction was fully enzymatic with an estimated K m of 1.89 m m. On the other hand, methylglyoxal was a competitive inhibitor of the enzyme for pyruvate, the K i being in the 1 m m range. The reaction was inhibited in the presence of HgCl 2. The reaction products were quantitatively identified as acetyl-CoA and formic acid. A mechanism for the reaction is proposed.

Glucose formation from methylglyoxal in rat hepatocytes

Metliylglyoxal metabolism is important because changes in the concentration of methylglyoxal may affect cell growth (Szent-Gyorgyi, 1967). Methylglyoxal is known t o be catabolized in liver via the glyoxalase system (glyoxalase I and I I ) (Racker, 195 I ) ; this leads t o the formation of D-lactate, which is poorly metabolized by the hepatocytes. However, the presence of akctoaldehyde dehydrogenase, which catalyses the direct oxidation of methylglyoxal to pyruvate in liver, has been shown (Monder, 1967; Ray & Ray, 1982). We undertook this work to test the possible physiological significance of the degradation of niethylglyoxal through the a-ketoaldehyde dehydrogenase pathway. ttepatocytes from 48-11-starved rats were isolated by the simplified procedure of Rotnero & Vifia (1983). Metabolites were determined by standard enzymic methods, as described in Bernt & Bergnieyer (1974). Hepatocytes readily degrade methylglyoxal. The rate of disappearance of methylglyoxal from 4 nil of a 2 mM solution in the presence of approx. 80 m g of hepatocytes (fresh wt.) was 28.8 f 1.9pmol/min per g (four observations) in the first 2 min of incubation. The amount of niethylglyoxal metabolized through the a-ketoaldehyde dehydrogenases was estiniated as the proportion of mcthylglyoxal converted to L-lactate plus glucose. whereas the contribution of the glyoxalase pathway was estiiiiatcd by the formation of D-lactate. When 0.5 mM-tiiethylglyoxal was used, 40% of i t appeared as L lactate plus glucose. Similar values were found with 0.25 iiiM-methylglyoxal. h w e v e r , when higher concentrations were used the proportion of methylglyoxal converted to L-lactate plus glucose was lower. Indeed, with 2 nib1 -methylglyoxal only 20% was converted to glucose plus L-lactate. The addition of 2 mM-methylglyoxal together with 10 niM -ethanol, which inhibits glyconeogenesis from lactate by shifting the NAD'/NADH + H ratio (Krebs et al.. 1969). proiiioted a decrease in the rate o f gluconeogenesis and an accuiiiulation of L-lactate. This suggests that glucose formation from methyglyoxal proceeds via the a-keto aldehyde dchydrogenase, which yields pyruvatc. When Fisiologia, Facultad de ethanol is present pyruvate is converted to L-lactate rather than to glucose. The rate of glucose formation from 2 mM-iilethylglyoxal measured in the first 2 niin of incubation, i.e. before methylglyoxal was used up, was 0.68 t 0.17 pinol/min per g (four observations). This value niay be of physiological interest since the cells formed 0.99 f 0.79 pmol/niin per g (three observations) when a classical gluconcogcnic precursor, L-lactate, was added at the sanie concentration. The aniount of niethylglyoxal metabolized through the glyoxalase system, which yields D-lactate, was maximal in the first S niin and remained constant even after 30 tnin of the incubation (see Table 1). We did not observe changes in the amount of methyl glyoxal converted t o L-lactate plus glucose when the cells were depleted of their reduced glutathione content by treatment with diethylnialeate (Boyland & Chasseaud. 1968). This is not surprising because only catalytic concentrations of reduced glutathione are required for the functioning of the glyoxalase system. The possible role of methylglyoxal in carbohydrate metabolism was proposed as early as 1913 (Dakin & Dudley, 1913 a,b; Neuberg, 1913). The discovery that the glyoxalases give rise t o D-lactate (Lohmann, 1032; Rackcr, 195 1) suggested that niethylglyoxal played little role on the carbohydrate metabolism in liver. Recently, Sato ct al. (1980) showed that the forniation of niethylglyoxal in rat liver cells is a metabolic process. Here, we show that the conversion of methylglyoxal to pyruvate (evidenced as L-lactate plus glucose formation) is an active metabolic process, the rate of glucose fortnation from niethylglyoxal being 70% of that from L-lactate. The physiological important of the shunt dihydroxyacetone phosphate + methylglyoxal -+ pyruvate in glycolysis and glyconeogenesis is being studied in this laboratory. The fact that niethylglyoxal has been implicated in the control of cell division adds further interest to these studies.

Purification and characterization of NAD and NADP-linked alpha-ketoaldehyde dehydrogenases involved in catalyzing the oxidation of methylglyoxal to pyruvate.

Two alpha-ketoaldehyde dehydrogenases, one catalyzing the oxidation of methylglyoxal to pyruvate with NAD and the other with NADP, were isolated from goat liver and happened to be co-purified. Both the enzymes had been extensively purified to the point where only these two enzymes were present. By affinity chromatography on a thiol-Sepharose column, the two enzymes were separated. Molecular weight of both the enzymes was found to be 42,000 by gel filtration in a Sephadex G-200 column. Electrophoresis on sodium dodecyl sulfate-polyacrylamide gel revealed that the enzymes are composed of single subunits. Interaction with mercurials indicated the presence of SH group(s) in the active site of the NAD-linked enzyme only.

On the interaction of nucleotides and glycolytic intermediates with NAD-linked alpha-ketoaldehyde dehydrogenase.

The effect of different nucleotides and glycolytic intermediates was tested on the NAD-linked and NADP-linked alpha-ketoaldehyde dehydrogenases involved in the oxidation of methylglyoxal to pyruvate. ATP, GTP, and ADP strongly inhibit the NAD-linked enzyme whereas activity of the NADP-linked enzyme remained unaltered. NADP at a concentration much below its catalytic concentration strongly inhibited the NAD-linked enzyme. This NADP inhibition decreased with decreasing of the pH of the incubation medium. Fructose 1,6-bisphosphate stimulated and glyceraldehyde 3-phosphate inhibited the activity of the NAD-linked enzyme whereas dihydroxyacetone phosphate inhibited NADP-linked activity. The stimulatory effect of fructose 1,6-bisphosphate diminished with lowering of the pH value. The various effects by several key metabolites of the glycolytic pathway indicate a possible physiological role for these enzymes.

Some observations on the NADP+-linked oxidation of methylglyoxal catalysed by 2-Oxoaldehyde dehydrogenase.

In the oxidation of methylglyoxal by 2-oxoaldehyde dehydrogenase, the apparent Km value for NADP+ was about 2.5 times lower than the corresponding Km for NAD+; the apparent Km values for methylglyoxal and for the amine activator L-2-aminopropan-1-ol, with NADP+ as cofactor, were also different from those obtained with NAD+. In the presence of NADP+, the enzyme was not activated by P1, in contrast with the activation of the enzyme when NAD+ was used. The significance of the results is discussed.

α-Keto Aldehyde Dehydrogenase, An Enzyme That Catalyzes the Enzymic Oxidation of Methylglyoxal to Pyruvate

An enzyme which catalyzes the oxidation of methylglyoxal to pyruvic acid was partially purified from aqueous extracts of sheep liver acetone powders. NAD+ or NADP+ was necessary for the oxidation. Changes in methylglyoxal, pyruvate, and pyridine nucleotide were stoichiometrically equivalent. Of various carbonyl-containing compounds tested, only α-keto aldehydes were substrates. Enzyme activity was found only in the supernatant fraction of liver cells. Evidence is presented that the conversion of methylglyoxal to pyruvate was direct and did not involve its preliminary conversion to lactate. Activity increased up to pH 10.4 with no indication of a pH optimum. Km values for methylglyoxal with respect to NADP+ were smaller than with respect to NAD+. The ratio of rates of NAD+ to NADP+ reduction varied with the nature of the substrate and type of inhibitor. The name α-keto aldehyde dehydrogenase is suggested. The possible function of this new enzyme activity is discussed in relation to the suggested origins and physiological functions of methylglyoxal.

Oxidation of methylglyoxal to pyruvic acid by a sheep-liver enzyme

Oxidation of methylglyoxal to pyruvic acid by a sheep-liver enzyme