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At least 163 records · Page 9Linked to original sources
PubMed2000

Maillard reactions in lens proteins: methylglyoxal-mediated modifications in the rat lens.

The nonenzymatic Maillard reaction is thought to contribute to aging and cataract formation in the lens. As levels of methylglyoxal (MG) and glutathione (GSH) affect the reaction, we examined the relationship of these factors and determined the effect of a glyoxalase I inhibitor on the Maillard reaction. Rat lens cultures were maintained for up to 3 days in TC-199 medium with or without 20 m m glyceraldehyde (GLD) and 250 microm S-[N-hydroxy-N-(4-chlorophenyl) carbamoyl] glutathione diethyl ester (HCCG diester). We measured GSH, MG, D-lactate, glyoxalase I activity, immunoreactive MG-derived advanced glycation endproducts (MG-AGEs) and imidazolysine in organ cultured rat lenses. In vitro experiments with isolated rat lens proteins revealed that HCCG alone inhibited glyoxalase I activity in a dose-dependent manner. In organ cultured rat lens protein, GLD increased MG levels 24-fold, and the addition of HCCG diester further increased it by about two-fold. GSH levels fell sharply in the presence of GLD and this was prevented to some extent by the presence of HCCG diester. D-lactate production in the lens was suppressed by HCCG diester treatment. Dialysed lens proteins retained glyoxalase I activity, indicating that the enzyme was unaltered during incubation. MG-AGEs and imidazolysine levels were significantly higher (P<0.05) in GLD-treated lenses, but a combination of HCCG diester and GLD lowered immunoreactive MG-AGEs and imidazolysine levels compared to GLD alone. HCCG had no significant effect on MG-AGE formation in lens proteins incubated with GLD or MG. We conclude that exogenous GLD enhances MG and MG-AGE levels in the rat lens and that this increase is accompanied by a loss in GSH. In addition, inhibition of glyoxalase I promotes MG accumulation.

Animals↗
PubMed2001

The importance of hinge sequence for loop function and catalytic activity in the reaction catalyzed by triosephosphate isomerase.

We have determined the sequence requirements for the N-terminal protein hinge of the active-site lid of triosephosphate isomerase. The codons for the hinge (PVW) were replaced with a genetic library of all possible 8000 amino acid combinations. The most active of these 8000 mutants were selected using in vivo complementation of a triosephosphate isomerase-deficient strain of Escherichia coli, DF502. Approximately 0.3 % of the mutants complement DF502 with an activity that is between 10 and 70 % of wild-type activity. They all contain Pro at the first position. Furthermore, the sequences of these hinge mutants reveal that hydrophobic packing is very important for efficient formation of the enediol intermediate. However, the reduced catalytic activities observed are not due to increased rates of loop opening. To explore the relationship between the N-terminal and C-terminal hinges, three semi-active mutants from the N-terminal hinge selection experiment (PLH, PHS and PTF), and six active C-terminal hinge mutants from previous work (NSS, LWA, YSL, KTK, NPN, KVA) were combined to form 18 "double-hinge" mutants. The activities of these mutants suggest that the N-terminal and C-terminal hinge structures affect one another. It appears that specific side-chain interactions are important for forming a catalytically active enzyme, but not for preventing release of the unstable enediol intermediate from the active site of the enzyme. The independence of intermediate release on amino acid sequence is consistent with the absence of a "universal" hinge sequence in structurally related enzymes.

Amino Acid Sequence↗
PubMed2001

Accumulation of methylglyoxal in anaerobically grown Escherichia coli and its detoxification by expression of the Pseudomonas putida glyoxalase I gene.

Anaerobic glycerol fermentation by Escherichia coli strains expressing genes from the Klebsiella pneumoniae dha regulon showed that cell growth and 1,3-propanediol (1,3-PD) production are significantly inhibited when 5 g/L or higher of glycerol is initially present. One reason for this inhibition may be methylglyoxal (MG) accumulation. Assays of both intracellular and extracellular MG levels indicated an accumulation of MG in anaerobic glycerol fermentation of transgenic E. coli. Pseudomonas putida glyoxalase I was expressed in the transgenic E. coli to enhance MG detoxification. The activity of glyoxalase I in the transgenic E. coli with the P. putida glyoxalase I under anaerobic conditions was 12-fold higher than that in the control cells. Compared to the control cells, the transgenic cells with the P. putida glyoxalase I displayed a reduction of 35-43% in intracellular MG and a decrease of 30% in extracellular MG. These decreases were statistically significant (P>94). Furthermore, the expression of the P. putida glyoxalase I in the transgenic E. coli markedly improved cell growth and resulted in a 50% increase in 1,3-PD production.

Anaerobiosis↗
PubMed1985

The effects of methylglyoxal on central synaptic transmission in the isolated nerve cord of the cockroach. (Periplaneta americana L).

Methylglyoxal (10(-5) to 1.5 X 10(-4) M) was found to have excitatory effects on synaptic transmission in the isolated 6th abdominal ganglion of the cockroach. There was a concentration-dependent depolarization of the giant interneurones which was accompanied by an increase in the amplitude and duration of electrically evoked excitatory postsynaptic potentials. The frequency of spontaneous activity was also increased.

Aldehydes↗
PubMed1986

Effects of methylglyoxal on central and peripheral cholinergic responses.

Methylglyoxal (MG) has been shown to have a depolarizing effect on the giant interneurones of the isolated 6th abdominal ganglion of the cock-roach. This effect of MG was inhibited by concentrations of nicotine, d-tubocurarine and physostigmine which blocked transmission at the cholinergic cercal nerve-giant interneurone synapse. MG (5 X 10(-5) to 5 X 10(-4) M) produced concentration-dependent contractures of the isolated frog rectus abdominis muscle which were inhibited by d-tubocurarine (10(-4) M) and physostigmine (10(-6) M). MG enhanced the action of acetylcholine and inhibited KCl-evoked contractures whereas it had no effect on the response to carbachol. It is concluded that MG appears to act as a cholinomimetic in both the peripheral and central nervous systems.

Aldehydes↗
PubMed1996

Interaction of aldehydes with glyoxalase I and the status of several aldehyde metabolizing enzymes of Ehrlich ascites carcinoma cells.

The possible effect of several physiologically important aldehydes has been tested on partially purified glyoxalase I of Ehrlich ascites carcinoma (EAC) cells. The results indicate that D, and L-lactaldehyde are strong non-competitive inhibitors of glyoxalase I and the effect with the D-isomer is more pronounced, whereas both D,L-glyceraldehyde and acetaldehyde are moderately inhibitory and the nature of inhibition is strictly competitive. Moreover, D,L-glyceraldehyde strongly inhibits the utilization of methylglyoxal by intact EAC cells. A search for the presence of several aldehyde metabolizing enzymes in EAC cells indicates that non-specific aldehyde reductase, methylglyoxal reductase, aldehyde dehydrogenase and alcohol dehydrogenase are apparently absent in this rapidly growing, highly de-differentiated malignant cell.

Acetaldehyde↗
PubMed1981

Isolation and characterization of cAMP suppressor mutants of Escherichia coli K12.

We have isolated spontaneous and chemically induced revertants of cya mutant strains of Escherichia coli. Three different classes of revertants were obtained. One class consisted of primary site revertants; a second class was pseudorevertants that had phenotypically reverted to wild type but retaining the original cya mutant and the third class of revertants, designated csm, were pseudorevertants hypersensitive to exogenous cAMP. Transductional analysis of the csm mutation indicated the mechanism of suppression in these strains was intergenic. The csm mutation and hypersensitivity to cAMP map in or near the crp gene. Growth of the csm strains on PTS (phosphoenolpyruvate phosphotransferase system) and non-PTS substrates was inhibited by 5 mM cAMP. The csm strains were found to accumulate toxic levels of methylglyoxal when grown on non-PTS substrates in the presence of exogenous cAMP. All csm strains were sensitive to catabolite repression mediated by alpha-methylglucoside. Revertants selected as resistant to cAMP fell into four major classes that could be distinguished by their fermentation patterns in the presence and absence of cAMP as well as by their growth response to streptomycin in the presence of cAMP.

Adenylyl Cyclases↗
PubMed1996

Reduction of methylglyoxal in Escherichia coli K12 by an aldehyde reductase and alcohol dehydrogenase.

Two enzymes, one NADPH-dependent and another NADH-dependent which catalyze the reduction of methylglyoxal to acetol have been isolated and substantially purified from crude extracts of Escherichia coli K12 cells. Substrate specificity and formation of acetol as the reaction product by both the enzymes, reversibility of NADH-dependent enzyme with alcohols as substrates and inhibitor study with NADPH-dependent enzyme indicate that NADPH-dependent and NADH-dependent enzymes are identical with an aldehyde reductase (EC 1.1.1.2) and alcohol dehydrogenase (EC 1.1.1.1) respectively. The K(m) for methylglyoxal have been determined to be 0.77 mM for NADPH-dependent and 3.8 mM for NADH-dependent enzyme. Stoichiometrically equimolar amount of acetol is formed from methylglyoxal by both NADPH- and NADH-dependent enzymes. In phosphate buffer, both the enzymes are active in the pH range of 5.8-6.6 with no sharp pH optimum. Molecular weight of both the enzymes were found to be 100,000 +/- 3,000 by gel filtration on a Sephacryl S-200 column. Both NADPH- and NADH-dependent enzymes are sensitive to sulfhydryl group reagents.

Alcohol Dehydrogenase↗
PubMed1975

Catabolism of D-fructose and D-ribose by Pseudomonas doudoroffii. I. Physiological studies and mutant analysis.

Pseudomonas doudoroffii, a strict aerobe of marine origin, was able to utilize fructose and ribose but not glucose, gluconate, or other hexoses, pentoses, or sugar alcohols as sole sources of carbon and energy. Evidence was presented indicating that in this organism fructose was utilized via an inducible P-enolpyruvate: fructose phosphotransferase system (FPTS) which catalyzed the phosphorylation of fructose in the 1 position. The resulting fructose-1-P (F-1-P) was converted to fructose-1,6-P2 (FDP) by means of an inducible 1-P-fructokinase (1-PFK). The subsequent conversion of FDP to pyruvate involved enzymes of the Embden-Meyerhof pathway (EMP) which, with the exception of glyceraldehyde-3-P dehydrogenase (G3PDH), were constitutive. Two G3PDH activities were detected, one of which was inducible and NAD-dependent while the other was constitutive and NADP-dependent. Cell-free extracts of P. doudoroffii also contained enzymes of the methylglyoxal pathway (MGP) which converted dihydroxyacetone-P to pyruvate. The low specific activities of enzymes of this pathway as compared to the EMP suggested that the major route of FDP catabolism was via the latter pathway. 2. Ribose catabolism appeared to involve an inducible uptake system and an inducible ribokinase, the resulting ribose-5-P being converted to glyceraldehyde-3-P and fructose-6-P (F-6-P) by means of constitutive activities of the pentose-P pathway. The F-6-P formed as a result of these reactions was converted to FDP by means of a constitutive 6-P-fructokinase (6-PFK). Since no activity converting fructose or F-1-P to F-6-P could be detected in cell-free extracts of P. doudoroffii, the results suggested that fructose and ribose were catabolized via 1-PFK and 6-PFK, respectively, the two pathways converging at the level of FDP. Further evidence for this suggestion was obtained from a mutant which lacked an NAD-dependent G3PDH, accumulated FDP from both fructose and ribose, and was not able to grow on either of these compounds. 3. Ribose grown cells had increased amounts of the fructose uptake system and 1-PFK suggesting that a compound (or compounds) common to the catabolism of both fructose and ribose acted as the inducer(s) of these activities. Evidence was presented suggesting that the probable inducer(s) of 1-PFK and FPTS could be FDP, glyceraldehyde-3-P, or dihydroxyacetone-P. 4. A mutant unable to grow on fructose was characterized and found to lack FPTS while retaining 1-PFK and other enzyme activities of the EMP and MGP, indicating that a functional FPTS was essential for growth on fructose and suggesting that all or most of this sugar was catabolized via F-1-P.

Dihydroxyacetone Phosphate↗
PubMed1979

Immunofluorescent serum gliadin antibodies in children with coeliac disease and various malabsorptive disorders. I. Technique, clinical evaluation and diagnostic use of a gliadin antibody assay using pyruvic aldehyde-treated human red cells.

An immunofluorescent gliadin antibody assay is described using pyruvic aldehyde-stabilized human erythrocytes coated with gliadin. Fifty coeliac children all had high serum IgG-antigliadin titres during a normal diet or a challenge with gluten. On a gluten-free diet (30 children), titres were much lower. In patients followed-up for one year on a gluten-free diet, an initial rise in titres was followed by a slow decline. On challenge, IgG-antigliadin titres showed a slow rise or persistence at the same level in most patients. Fifty-two percent of control children with malabosrptive disorders, but without the typical "flat" mucosal lesion on jejunal biopsy, were shown to have positive titres in their sera, as were 6% of normal children and 4% of adult blood donors. The fluorescent antibody technique was compared with methods commonly used to detect wheat-protein antibodies, and was found to be superior to all of them. The immunofluorescent gliadin antibody assay appears to be useful in following-up children with coeliac disease, and in selecting patients for jejunal biopsy, although it does not replace biopsy.

Antibodies↗
PubMed1984

A comparative study on proliferation, macromolecular synthesis and energy metabolism of in vitro-grown Ehrlich ascites tumor cells in the presence of glucosone, galactosone and methylglyoxal.

Proliferation of in vitro grown Ehrlich ascites tumor cells is completely inhibited by 0.2-0.4 mM methylglyoxal and 1-2 mM glucosone or galactosone without severely affecting viability (dye exclusion test); no phase-specific arrest of cell growth is observed. Incorporation of [14C] thymidine into the acid-insoluble fraction of the cells decreases within a few minutes to less than 50% of that in controls in the presence of 0.4 mM methylglyoxal, and 2 mM glucosone or galactosone causes a comparable inhibition of DNA synthesis after 2 h or 4 h, respectively. The action of 0.4 mM methylglyoxal inhibits incorporation of [14C] leucine within a few minutes by more than 70%, while 2 mM glucosone and galactosone are significantly less effective (50%-60% inhibition after 12 h). While methylglyoxal and galactosone do not severely affect lactate production of the cells, 2 mM glucosone reduces glycolysis by 60%-70%; ATP/ADP ratios did not fall below 3.5 in the presence of the inhibitors (controls 4-6). It is suggested that the reaction potentialities of the oxaldehyde function of the inhibitors play an important role in their growth-inhibitory activity, besides exerting a specific effect on hexokinase (glucosone) and UTP-trapping activity.

Adenosine Diphosphate↗
PubMed1982

Oxidation, photosensitized by certain diketones, of enzymes and protection against such oxidation by histidine derivatives.

Bovine milk lactoperoxidase, eel acetylcholinesterase, and Aeromonas aminopeptidase were photooxidized and inactivated in broad-spectrum visible light in the presence of 2,3-butanedione and 1-phenyl-1,2-propanedione. Methylglyoxal caused similar effects at 254 nm. 2-Thiol-L-histidine and 3-methyl-L-histidine protected the enzymes against photoinactivation more effectively then N3-, even at a molar ratio of 2:1 (protector to enzyme). These compounds also delayed the photoinactivation of acetylcholinesterase, induced by ultraviolet light.

Acetylcholinesterase↗
PubMed1984

Methylglyoxal inhibits the translation of natural and chemically decapped mRNAs.

Methylglyoxal was a weak inhibitor of translation in the reticulocyte-lysate cell-free system and it did not display cap-dependent inhibition. A similar inhibition was obtained in a wheat-germ cell-free system that displayed extensive cap-dependent inhibition with the cap analogue 7-methylguanosine phosphate. These results show that the chemical reaction of methylglyoxal with 7-methylguanosine is not the mechanism for the inhibition of protein synthesis by methylglyoxal and that methylglyoxal is a weak general inhibitor of translation.

Aldehydes↗
PubMed1992

D-lactate concentrations in blood, urine and sweat before and after exercise.

The purpose of this study was to investigate changes in the concentrations of D-lactate, L-lactate, pyruvate and methylglyoxal (MG) in body fluids after exercise. Eight untrained male students and five male students who were boat club members engaged in the exercise. Each subject performed runs of short and long duration. Compared to pre-exercise values plasma concentrations of D-lactate, L-lactate and pyruvate increased after running; in trained men by 3.6, 5.0, 3.4 times after short runs and by 1.5, 4.6, 2.0 times after long runs, and in untrained men by 3.0, 12.0, 1.6 times after short runs and 2.5, 5.6, 1.6 times after long runs, respectively. In all cases, the increase of L-lactate was always higher than that of D-lactate after running. The MG contents in red blood cells decreased markedly after running, especially in the untrained students. After short runs the MG concentration had decreased to 13% in the untrained men and 30% in the trained men, and after long runs the concentration had decreased to 41% in the untrained and 60% in the trained men. The MG in plasma and red blood cells appeared to have been utilized during relatively anaerobic exercise, especially by the untrained subjects. The D-lactate and related substances were also determined in urine, but the concentration of these substances showed no relationship to exercise. The D-lactate concentration in sweat samples tripled after short periods of running but the relative concentration to sodium ion concentration was not altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Molecular characteristics of methylglyoxal-modified bovine and human serum albumins. Comparison with glucose-derived advanced glycation endproduct-modified serum albumins.

The amino acid modification, gel filtration chromatographic, and electrophoretic characteristics of bovine and human serum albumins irreversibly modified by methylglyoxal (MG-SA) and by glucose-derived advanced glycation endproducts (AGE-SA) were investigated. Methylglyoxal selectively modified arginine residues at low concentration (1 mM); at high methylglyoxal concentration (100 mM), the extent of arginine modification increased and lysine residues were also modified. Both arginine and lysine residues were modified in AGE-SA. Analytical gel filtration HPLC of serum albumin derivatives suggested that the proportion of dimers and oligomers increased with modification in both low and highly modified MG-SA and AGE-SA derivatives relative to unmodified serum albumins. In SDS-PAGE analysis, dimers and oligomers of low-modified MG-SA were dissociated into monomers, but not in highly modified MG-SA. MG-SA had increased anodic electrophoretic mobility under nondenaturing conditions at pH 8.6, indicating an increased net negative charge, which increased with extent of modification; highly modified MG-SA and AGE-SA had similar high electrophoretic mobilities. MG-SA derivatives were fluorescent: the fluorescence was characteristic of the arginine-derived imidazolone N delta-(5-methyl-4-imidazolon-2-yl)ornithine, but other fluorophores were also present. AGE-SA had similar fluorescence, attributed, in part, to glucose-derived imidazolones. AGE formed from glucose-modified proteins and AGE-like compounds formed from methylglyoxal-modified proteins may both be signals for recognition and degradation of senescent macromolecules.

Animals↗