The tumor promoting phorbol diester, 12-0-tetradecanoylphorbol-13-acetate (TPA) increases glyoxalase I and decreases glyoxalase II activity in human polymorphonuclear leukocytes

Glyoxalase I and II catalyze the formation and breakdown of S-lactoylglutathione respectively. Recent studies have implicated this com-pound as a possible mediator of immune and inflammatory responses. Incubation of human polymorphonuclear leukocytes with the tumor promoter, 12-0-tetradecanoylphorbol-13-acetate has been found to affect the activities of both glyoxalase enzymes in an interrelated manner. The diester either increases the activity of glyoxalase I or decreases the activity of glyoxalase II or has both effects. It is suggested that a subsequent increase in S-lactoylglutathione might mediate some or all of the effects of the phorbol diesters.     

Paclobutrazol mitigates salt stress in <Emphasis Type="Italic">indica</Emphasis> rice seedlings by enhancing glutathione metabolism and glyoxalase system

Stress-induced methylglyoxal (MG) functions as a toxic molecule, inhibiting plant physiological processes such as photosynthesis and antioxidant defense systems. In the present study, an attempt was made to investigate the MG detoxification through glutathione metabolism in indica rice [Oryza sativa L. ssp. indica cv. Pathumthani 1] under salt stress by exogenous foliar application of paclobutrazol (PBZ). Fourteen-day-old rice seedlings were pretreated with 15 mg L^?1 PBZ foliar spray. After 7 days, rice seedlings were subsequently exposed to 0 (control) or 150 mM NaCl (salt stress) for 12 days. Prolonged salt stress enhanced the production of MG molecules and the oxidation of proteins, leading to decreased activity of glyoxalase enzymes, glyoxalase I (Gly I) and glyoxalase II (Gly II). Consequently, the decreased glyoxalase activities were also associated with a decline in reduced glutathione (GSH) content and glutathione reductase (GR) activity. PBZ pretreatment of rice seedlings under salt stress significantly lowered MG production and protein oxidation, and increased the activities of both Gly I and Gly II. PBZ also increased GSH content and GR activity along with the up-regulation of glyoxalase enzymes, under salt stress. In summary, salinity induced a high level of MG and the associated oxidative damage, while PBZ application reduced the MG toxicity by up-regulating glyoxalase and glutathione defense system in rice seedlings.     

Modification of the glyoxalase system during the functional activation of human neutrophils

The glyoxalase system catalyses the metabolism of methylglyoxal to D-lactic acid, via the intermediate S-D-lactoylglutathione. It is present in human neutrophils and undergoes a significant modification during functional activation--induction of chemotaxis, phagocytosis and degranulation. During the activation of neutrophils with serum-opsonised zymosan and the tumour-promoting phorbol diester 12-O-tetradecanoylphorbol 13-acetate, the activity of glyoxalase I increases and the activity of glyoxalase II decreases by 20-40% of their activities in resting cells, in the initial 10 min of the activation period. Determination of the Michaelis constant, Km, and the apparent maximum velocity, Vmax, for these enzymatic reactions indicates that the change in activity is due to a non-competitive activation and inhibition of glyoxalase I and glyoxalase II, respectively. This is consistent with a modification of the glyoxalase enzyme protein during the activation response. This modification occurs under aerobic and anaerobic incubation conditions. The concentration of S-D-lactoylglutathione increases approx. 100% of the resting cell concentration during the initial 10 min of the activation period. The presence of S-D-lactoylglutathione in neutrophils may be related to its ability to stimulate microtubule assembly.     

Proline and glycinebetaine enhance antioxidant defense and methylglyoxal detoxification systems and reduce NaCl-induced damage in cultured tobacco cells

Salt stress impairs reactive oxygen species (ROS) and methylglyoxal (MG) detoxification systems, and causes oxidative damage to plants. Up-regulation of the antioxidant and glyoxalase systems provides protection against NaCl-induced oxidative damage in plants. Thiol–disulfide contents, glutathione content and its associated enzyme activities involved in the antioxidant defense and glyoxalase systems, and protein carbonylation in tobacco Bright Yellow-2 cells grown in suspension culture were investigated to assess the protection offered by proline and glycinebetaine against salt stress. Salt stress increased protein carbonylation, contents of thiol, disulfide, reduced (GSH) and oxidized (GSSG) forms of glutathione, and the activity of glutathione-S-transferase and glyoxalase II enzymes, but decreased redox state of both thiol–disulfide and glutathione, and the activity of glutathione peroxidase and glyoxalase I enzymes involved in the ROS and MG detoxification systems. Exogenous application of proline or glycinebetaine resulted in a reduction of protein carbonylation, and in an increase in glutathione redox state and activity of glutathione peroxidase, glutathione-S-transferase and glyoxalase I under salt stress. Neither proline nor glycinebetaine, however, had any direct protective effect on NaCl-induced GSH-associated enzyme activities. The present study, therefore, suggests that both proline and glycinebetaine provide a protective action against NaCl-induced oxidative damage by reducing protein carbonylation, and enhancing antioxidant defense and MG detoxification systems.     

Trypanothione-dependent glyoxalase I in Trypanosoma cruzi

The glyoxalase system, comprizing glyoxalase I and glyoxalase II, is a ubiquitous pathway that detoxifies highly reactive aldehydes, such as methylglyoxal, using glutathione as a cofactor. Recent studies of Leishmania major glyoxalase I and Trypanosoma brucei glyoxalase II have revealed a unique dependence upon the trypanosomatid thiol trypanothione as a cofactor. This difference suggests that the trypanothione-dependent glyoxalase system may be an attractive target for rational drug design against the trypanosomatid parasites. Here we describe the cloning, expression and kinetic characterization of glyoxalase I from Trypanosoma cruzi. Like L. major glyoxalase I, recombinant T. cruzi glyoxalase I showed a preference for nickel as its metal cofactor. In contrast with the L. major enzyme, T. cruzi glyoxalase I was far less fast-idious in its choice of metal cofactor efficiently utilizing cobalt, manganese and zinc. T. cruzi glyoxalase I isomerized hemithio-acetal adducts of trypanothione more than 2400 times more efficiently than glutathione adducts, with the methylglyoxal adducts 2-3-fold better substrates than the equivalent phenylglyoxal adducts. However, glutathionylspermidine hemithioacetal adducts were most efficiently isomerized and the glutathionylspermidine-based inhibitor S-4-bromobenzylglutathionylspermidine was found to be a potent linear competitive inhibitor of the T. cruzi enzyme with a K(i) of 5.4+/-0.6 microM. Prediction algorithms, combined with subcellular fractionation, suggest that T. cruzi glyoxalase I localizes not only to the cytosol but also the mitochondria of T. cruzi epimastigotes. The contrasting substrate specificities of human and trypanosomatid glyoxalase enzymes, confirmed in the present study, suggest that the glyoxalase system may be an attractive target for anti-trypanosomal chemotherapy.     

Functional properties of a lymphocyte subpopulation responding to low suboptimal doses of concanavalin A

Incubation of human peripheral blood lymphocytes with concanavalin A (Con A), in a low suboptimal dose (0.5 microgram/ml), results in formation of the cells that inhibit proliferation of autologous cells in cultures activated with optimal but not with suboptimal dose of the mitogen. Nevertheless, 50 micrograms/ml Con A-activated cells efficiently suppress proliferation everywhere. Cell preincubation during 18 h before Con A activation leads to a reduction of lymphocyte responses to the mitogen in cultures reactivated with 5 micrograms/ml Con A in a mixture with autologous lymphocytes, containing no mitogen. Activation of T-T helper cells providing suppressor T cells differentiation seems to take place in the presence of a low suboptimal dose of Con A. Besides, 0.5 microgram/ml Con A prevents the preincubation-induced elimination of some lymphocytes responding to an optimal dose of Con A and autologous lymphocytes.     

Exogenous jasmonic acid modulates the physiology,antioxidant defense and glyoxalase systems in imparting drought stress tolerance in different Brassica species

This study examined the ability of jasmonic acid (JA) to enhance drought tolerance in different Brassica species in terms of physiological parameters, antioxidants defense, and glyoxalase system. Ten-day-old seedlings were exposed to drought (15 % polyethylene glycol, PEG-6000) either alone or in combination with 0.5 mM JA. Drought significantly increased lipoxygenase activity and oxidative stress, levels of malondialdehyde and H₂O₂. Drought reduced seedling biomass, chlorophyll (chl) content, and leaf relative water content (RWC). Drought increased proline, oxidized ascorbate (DHA) and glutathione disulfide (GSSG) levels. Drought affected different species differently: in B. napus, catalase (CAT) and glyoxalase II (Gly II) activities were decreased, while glutathione-S-transferase (GST) and glutathione peroxidase (GPX) activities were increased in drought-stressed compared to unstressed plants; in B. campestris, activities of glutathione reductase (GR), glyoxalase I (Gly I), GST, and GPX were increased, monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), CAT and other enzymes were decreased; in B. juncea, activities of ascorbate peroxidase, GR, GPX, Gly I were increased; Gly II activity was decreased and other enzymes did not change. Spraying drought-stressed seedlings with JA increased GR and Gly I activities in B. napus; increased MDHAR activity in B. campestris; and increased DHAR, GR, GPX, Gly I and Gly II activities in B. juncea. JA improved fresh weight, chl, RWC in all species, dry weight increased only in B. juncea. Brassica juncea had the lowest oxidative stress under drought, indicating its natural drought tolerance capacity. The JA improved drought tolerance of B. juncea to the highest level among studied species.     

Selenium Pretreatment Upregulates the Antioxidant Defense and Methylglyoxal Detoxification System and Confers Enhanced Tolerance to Drought Stress in Rapeseed Seedlings

In order to observe the possible regulatory role of selenium (Se) in relation to the changes in ascorbate (AsA) glutathione (GSH) levels and to the activities of antioxidant and glyoxalase pathway enzymes, rapeseed (Brassica napus) seedlings were grown in Petri dishes. A set of 10-day-old seedlings was pretreated with 25 μM Se (Sodium selenate) for 48 h. Two levels of drought stress (10% and 20% PEG) were imposed separately as well as on Se-pretreated seedlings, which were grown for another 48 h. Drought stress, at any level, caused a significant increase in GSH and glutathione disulfide (GSSG) content; however, the AsA content increased only under mild stress. The activity of ascorbate peroxidase (APX) was not affected by drought stress. The monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) activity increased only under mild stress (10% PEG). The activity of dehydroascorbate reductase (DHAR), glutathione S-transferase (GST), glutathione peroxidase (GPX), and glyoxalase I (Gly I) activity significantly increased under any level of drought stress, while catalase (CAT) and glyoxalase II (Gly II) activity decreased. A sharp increase in hydrogen peroxide (H₂O₂) and lipid peroxidation (MDA content) was induced by drought stress. On the other hand, Se-pretreated seedlings exposed to drought stress showed a rise in AsA and GSH content, maintained a high GSH/GSSG ratio, and evidenced increased activities of APX, DHAR, MDHAR, GR, GST, GPX, CAT, Gly I, and Gly II as compared with the drought-stressed plants without Se. These seedlings showed a concomitant decrease in GSSG content, H₂O₂, and the level of lipid peroxidation. The results indicate that the exogenous application of Se increased the tolerance of the plants to drought-induced oxidative damage by enhancing their antioxidant defense and methylglyoxal detoxification systems.     

γδ-Dioxovalerate as a substrate for the glyoxalase enzyme system

1. Crude gammadelta-dioxovalerate was synthesized from laevulinate by two different methods and was purified by Sephadex chromatography. Some analytical reactions of the compound are described. 2. gammadelta-Dioxovalerate is a substrate for glyoxalase I and the GSH derivative formed by this enzyme is hydrolysed by glyoxalase II to form d-alpha-hydroxyglutarate. The K(m) of glyoxalase I for gammadelta-dioxovalerate is 1.0x10(-3)m at pH5.8.3. The u.v.-absorption spectrum of thiol ester, synthesized enzymically from gammadelta-dioxovalerate and GSH by glyoxalase I, is almost identical with that for S-lactoylglutathione. Some optical properties of this thiol ester were measured. 4. Attempts to show reversibility of the glyoxalase system reactions with d-alpha-hydroxyglutarate as substrate were unsuccessful. 5. The possible metabolic role of the gammadelta-dioxovalerate reaction is discussed. It is suggested that one of the metabolic functions of the glyoxalase system may be to provide a mechanism for the entry of this compound into the tricarboxylic acid cycle.     

Relationship among activation of the Na+/H+ antiporter, ornithine decarboxylase induction, and DNA synthesis

The relationship among activation of the Na+/H+ antiporter, ornithine decarboxylase, and DNA synthesis was examined with bovine small lymphocytes stimulated by concanavalin A (Con A). The Na+/H+ antiport activity was activated immediately after addition of concanavalin A; the maximum was reached 1 h after Con A addition and the activation continued at least 6 h. With increasing concanavalin A concentrations, the activities of the Na+/H+ antiporter, ornithine decarboxylase, and DNA synthesis increased in a parallel manner. In the presence of HCO3- in the medium, the internal alkalinization of lymphocytes was not induced by Con A. Ornithine decarboxylase and DNA synthetic activities were not inhibited by 5-(N-ethyl-N-isopropyl) amiloride (EIPA), a specific inhibitor of the Na+/H+ antiporter. In contrast, in the absence of HCO3- in the medium, the internal pH was alkalinized approximately 0.06 pH units by Con A. EIPA did inhibit the alkalinization of the internal pH or DNA synthesis significantly. Ornithine decarboxylase activity was not inhibited by EIPA. These results indicate that the activation of a Na+/H+ antiporter is not a trigger for cell proliferation, but its activation is important probably through the maintenance of the internal pH optimum, especially in HCO3(-)-free medium.     

Involvement of arginine residues in glutathione binding to yeast glyoxalase I

Yeast glyoxalase I was inactivated by arginine-specific reagents. Inactivation by 2,3-butanedione, phenylglyoxal and camphorquinone 10-sulfonic acid followed pseudo first-order kinetics with the rate dependent upon modifier concentration. Extrapolation to complete inactivation showed modification of approx. two of the ten total arginyl residues in the native enzyme, with approx. one residue protected by glutathione (GSH) as determined by [ring-14C]phenylglyoxal incorporation. GSH protected the enzyme from inactivation, whereas methylglyoxal, glutathione disulfide (GSSG) and dithiothreitol afforded partial protection. The hemimercaptal of methylglyoxal and GSH and the catalytic product, S-lactoylglutathione provided substantial protection from inactivation. A methyl ester placed on the glycyl carboxyl moiety of GSH abolished all protective capability which suggests that this functionality is responsible for binding to the enzyme. These results provide the first evidence concerning the molecular binding mode of GSH to an enzyme. Arginyl residues are proposed as anionic recognition sites for glutathione on other GSH-utilizing enzymes.     

Lipoprotein substrates of lipoprotein lipase and hepatic triacylglycerol lipase from human post-heparin plasma.

The number and the substrate specificities of glutathione thiol esterases of human red blood cells have been investigated by gel electrophoresis and isoelectric focusing and staining methods devised for the location of these enzymes on gels. Several glutathione thiol esterase forms, both unspecific (with respect to the S-acyl group of the substrate) and specific were found. Electrophoresis on both polyacrylamide and agarose gels resolved three enzyme components with apparently similar substrate specificity. Isoelectric focusing in liquid column separated two unspecific thiol esterase components with S-lactoylglutathione (pI = 8.4) and S-propionylglutathione (pI = 8.1) as the best substrates, respectively, and two specific enzymes, S-formylglutathione hydrolase (pI = 5.2) and S-succinylglutathione hydrolase (pI = 9.0). Isoelectric focusing on polyacrylamide gel resolved nine unspecific glutathione thiol esterase bands (between pH values 7.0 and 8.4). Partially purified glyoxalase II (S-2-hydroxyacylglutathione hydrolase, EC 3.1.2.6) from erythrocytes or liver still gave three components on electrophoresis and several activity bands on gel electrofocusing. These results indicate that human red cells contain at least four separate glutathione thiol esterases. Glyoxalase II, one of these enzymes, apparently occurs in multiple forms. These were neither influenced by preptreatment of the samples with neuraminidase or thiols nor were interconvertible during the fractionations.     

Relative distribution of glutathione transferase, glyoxalase I and glyoxalase II in helminths

Glutathione transferase, glyoxalase I and glyoxalase II activities were not evenly distributed among the major helminth groups. Intestinal cestodes and digeneans had higher glutathione transferase activity than parasitic nematodes. High glyoxalase II activity was found in cestodes and digeneans but no glyoxalase I was detectable. Glyoxalase I and II were both detected in nematodes. These results are discussed in relation to the enzymes' suggested role in protection against secondary lipid peroxidation products.     

Transgenic tobacco plants overexpressing glyoxalase enzymes resist an increase in methylglyoxal and maintain higher reduced glutathione levels under salinity stress

The mechanism behind enhanced salt tolerance conferred by the overexpression of glyoxalase pathway enzymes was studied in transgenic vis-à-vis wild-type (WT) plants. We have recently documented that salinity stress induces higher level accumulation of methylglyoxal (MG), a potent cytotoxin and primary substrate for glyoxalase pathway, in various plant species [Yadav, S.K., Singla-Pareek, S.L., Ray, M., Reddy, M.K. and Sopory, S.K. (2005) MG levels in plants under salinity stress are dependent on glyoxalase I and glutathione. Biochem. Biophys. Res. Commun. 337, 61-67]. The transgenic tobacco plants overexpressing glyoxalase pathway enzymes, resist an increase in the level of MG that increased to over 70% in WT plants under salinity stress. These plants showed enhanced basal activity of various glutathione related antioxidative enzymes that increased further upon salinity stress. These plants suffered minimal salinity stress induced oxidative damage measured in terms of the lipid peroxidation. The reduced glutathione (GSH) content was high in these transgenic plants and also maintained a higher reduced to oxidized glutathione (GSH:GSSG) ratio under salinity. Manipulation of glutathione ratio by exogenous application of GSSG retarded the growth of non-transgenic plants whereas transgenic plants sustained their growth. These results suggest that resisting an increase in MG together with maintaining higher reduced glutathione levels can be efficiently achieved by the overexpression of glyoxalase pathway enzymes towards developing salinity stress tolerant plants.     

S-D-lactoylglutathione in resting and activated human neutrophils

Zymosan particles opsonised with human serum factors functionally activate human neutrophils and induce a substantial modification of the human neutrophil cytosolic glyoxalase system. The activity of glyoxalase I increases and the activity of glyoxalase II decreases by 20-40% of their resting cell activities during the initial 10 min of activation. The cellular concentration of the glyoxalase intermediate S-D-lactoylglutathione increases by ca. 100% of resting cell levels during this period. This modification may be related to the ability of S-D-lactoylglutathione to stimulate the assembly of microtubules.     

Proline and betaine provide protection to antioxidant and methylglyoxal detoxification systems during cold stress in <Emphasis Type="Italic">Camellia sinensis</Emphasis> (L.) O. Kuntze

The aim of this study was to monitor the influence of proline and betaine exposure on antioxidant and methylglyoxal (MG) detoxification system during cold stress in Camellia sinensis (L.) O. Kuntze. Cold stress enhanced MG and lipid peroxidation levels in tea bud (youngest topmost leaf). This increase was resisted upon the exposure of tea bud to proline and betaine. Exposure of tea bud with proline and betaine also help in maintaining thiol/disulfide ratio during cold stress. Proline exposure enhanced glutathione-S-transferase and glutathione reductase (GR) activity, while betaine exposure increased only GR activity during cold stress. Furthermore, effect of proline/betaine was studied on glyoxalase pathway enzymes that are involved in MG detoxification and comprise of two enzymes glyoxalase I and glyoxalase II. Both proline and betaine showed protective effect on glyoxalase I and activating effect on glyoxalase II during cold stress in tea bud. This investigation, therefore, suggest that proline and betaine might provide protection to cold stress in tea by regulating MG and lipid peroxidation formation as well as by activating or protecting some of antioxidant and glyoxalase pathway enzymes.     

Yeast glyoxalase I is a monomeric enzyme with two active sites

The tertiary structure of the monomeric yeast glyoxalase I has been modeled based on the crystal structure of the dimeric human glyoxalase I and a sequence alignment of the two enzymes. The model suggests that yeast glyoxalase I has two active sites contained in a single polypeptide. To investigate this, a recombinant expression clone of yeast glyoxalase I was constructed for overproduction of the enzyme in Escherichia coli. Each putative active site was inactivated by site-directed mutagenesis. According to the alignment, glutamate 163 and glutamate 318 in yeast glyoxalase I correspond to glutamate 172 in human glyoxalase I, a Zn(II) ligand and proposed general base in the catalytic mechanism. The residues were each replaced by glutamine and a double mutant containing both mutations was also constructed. Steady-state kinetics and metal analyses of the recombinant enzymes corroborate that yeast glyoxalase I has two functional active sites. The activities of the catalytic sites seem to be somewhat different. The metal ions bound in the active sites are probably one Fe(II) and one Zn(II), but Mn(II) may replace Zn(II). Yeast glyoxalase I appears to be one of the few enzymes that are present as a single polypeptide with two active sites that catalyze the same reaction.     

Acute hypoxic pulmonary vasoconstriction in conscious dogs decreases renin and is unaffected by losartan.

Acute hypoxic pulmonary vasoconstriction (HPV) may be mediated by vasoactive peptides. We studied eight conscious, chronically tracheostomized dogs kept on a standardized dietary sodium intake. Normoxia (40 min) was followed by hypoxia (40 min, breathing 10% oxygen, arterial oxygen pressures 36 +/- 1 Torr) during both control (Con) and losartan experiments (Los; iv infusion of 100 microg. min-1. kg-1 losartan). During hypoxia, minute ventilation (by 0.9 l/min in Con, by 1.3 l/min in Los), cardiac output (by 0.36 l/min in Con, by 0.30 l/min in Los), heart rate (by 11 beats/min in Con, by 30 beats/min in Los), pulmonary artery pressure (by 9 mmHg in both protocols), and pulmonary vascular resistance (by 280 and 254 dyn. s. cm-5 in Con and Los, respectively) increased. Mean arterial pressure and systemic vascular resistance did not change. In Con, PRA decreased from 4.2 +/- 0.7 to 2.5 +/- 0.5 ng ANG I. ml-1. h-1, and plasma ANG II decreased from 11.9 +/- 3.0 to 8.2 +/- 2.1 pg/ml. The renin-angiotensin system is inhibited during acute hypoxia despite sympathetic activation. Under these conditions, ANG II AT1-receptor antagonism does not attenuate HPV.     

Methylglyoxal resistance in Bacillus subtilis: contributions of bacillithiol‐dependent and independent pathways

Methylglyoxal (MG) is a toxic by‐product of glycolysis that damages DNA and proteins ultimately leading to cell death. Protection from MG is often conferred by a glutathione‐dependent glyoxalase pathway. However, glutathione is absent from the low‐GC Gram‐positive Firmicutes, such as Bacillus subtilis. The identification of bacillithiol (BSH) as the major low‐molecular‐weight thiol in the Firmicutes raises the possibility that BSH is involved in MG detoxification. Here, we demonstrate that MG can rapidly and specifically deplete BSH in cells, and we identify both BSH‐dependent and BSH‐independent MG resistance pathways. The BSH‐dependent pathway utilizes glyoxalase I (GlxA, formerly YwbC) and glyoxalase II (GlxB, formerly YurT) to convert MG to d ‐lactate. The critical step in this pathway is the activation of the KhtSTU K⁺ efflux pump by the S‐lactoyl‐BSH intermediate, which leads to cytoplasmic acidification. We show that cytoplasmic acidification is both necessary and sufficient for maximal protection from MG. Two additional MG detoxification pathways operate independent of BSH. The first involves three enzymes (YdeA, YraA and YfkM) which are predicted to be homologues of glyoxalase III that converts MG to d ‐lactate, and the second involves YhdN, previously shown to be a broad specificity aldo‐keto reductase that converts MG to acetol.