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PubMed1970

Gluconeogenesis in the kidney cortex. Flow of malate between compartments.

1. Kidney-cortex slices from starved rats were incubated with l-[U-(14)C]lactate or l-[U-(14)C]malate plus unlabelled acetate and the specific radioactivity of the glucose formed was determined. In parallel experiments the specific radioactivity of the glucose formed from [1-(14)C]acetate plus unlabelled l-lactate and l-malate was determined. 2. By analytical methods the major products formed from the substrates were measured. The glucose formed was purified by paper chromatography for determination of specific radioactivity. 3. The specific radioactivity of the glucose formed from l-[U-(14)C]lactate agrees with predictions of a model based on interaction of the gluconeogenic and the oxidative pathways. 4. The specific radioactivity of the glucose formed from l-[U-(14)C]malate agrees with the predicted value if rapid malate exchange between the cytosol and mitochondria is assumed. 5. The rate of malate exchange between compartments was estimated to be rapid and at least several times the rate of glucose formation. 6. The specific radioactivity of the glucose formed from [1-(14)C]acetate plus unlabelled l-lactate or l-malate agrees with the predictions from the model, again assuming rapid malate exchange between compartments. 7. Malate exchange between compartments together with reversible malate dehydrogenase activity in the mitochondria and cytosol also tends to equilibrate isotopically the NADH pool in these compartments. (3)H from compounds such as l-[2-(3)H]lactate, which form NAD(3)H in the cytosol, appears in part in water; and (3)H from dl-beta-hydroxy[3-(3)H]butyrate, which forms NAD(3)H in the mitochondria, appears in part in glucose, largely on C-4.

Acetates↗
PubMed2003

The plant homolog to the human sodium/dicarboxylic cotransporter is the vacuolar malate carrier.

Malate plays a central role in plant metabolism. It is an intermediate in the Krebs and glyoxylate cycles, it is the store for CO2 in C4 and crassulacean acid metabolism plants, it protects plants from aluminum toxicity, it is essential for maintaining the osmotic pressure and charge balance, and it is therefore involved in regulation of stomatal aperture. To fulfil many of these roles, malate has to be accumulated within the large central vacuole. Many unsuccessful efforts have been made in the past to identify the vacuolar malate transporter; here, we describe the identification of the vacuolar malate transporter [A. thaliana tonoplast dicarboxylate transporter (AttDT)]. This transporter exhibits highest sequence similarity to the human sodium/dicarboxylate cotransporter. Independent T-DNA [portion of the Ti (tumor-inducing) plasmid that is transferred to plant cells] Arabidopsis mutants exhibit substantially reduced levels of leaf malate, but respire exogenously applied [14C]malate faster than the WT. An AttDT-GFP fusion protein was localized to vacuole. Vacuoles isolated from Arabidopsis WT leaves exhibited carbonylcyanide m-chlorophenylhydrazone and citrate inhibitable malate transport, which was not stimulated by sodium. Vacuoles isolated from mutant plants import [14C]-malate at strongly reduced rates, confirming that this protein is the vacuolar malate transporter.

Amino Acid Sequence↗
PubMed1997

Factors affecting lactate and malate utilization by Selenomonas ruminantium.

Lactate utilization by Selenomonas ruminantium is stimulated in the presence of malate. Because little information is available describing lactate-plus-malate utilization by this organism, the objective of this study was to evaluate factors affecting utilization of these two organic acids by two strains of S. ruminantium. When S. ruminantium HD4 and H18 were grown in batch culture on DL-lactate and DL-malate, both strains coutilized both organic acids for the initial 20 to 24 h of incubation and acetate, propionate, and succinate accumulated. However, when malate and succinate concentrations reached 7 mM, malate utilization ceased, and with strain H18, there was a complete cessation of DL-lactate utilization. Malate utilization by both strains was also inhibited in the presence of glucose. S. ruminantium HD4 was unable to grow on 6 mM DL-lactate at extracellular pH 5.5 in continuous culture (dilution rate, 0.05 h-1) and washed out of the culture vessel. Addition of 8 mM DL-malate to the medium prevented washout on 6 mM DL-lactate at pH 5.5 and resulted in succinate accumulation. Addition of malate also increased bacterial protein, acetate, and propionate concentrations in continuous culture. These results suggest that 8 mM DL-malate enhances the ability of strain HD4 to grow on 6 mM DL-lactate at extracellular pH 5.5.

Animals↗
PubMed1983

Purification and characterization of a bifunctional L-(+)-tartrate dehydrogenase-D-(+)-malate dehydrogenase (decarboxylating) from Rhodopseudomonas sphaeroides Y.

A bifunctional enzyme, L-(+)-tartrate dehydrogenase-D-(+)-malate dehydrogenase (decarboxylating) (EC 1.1.1.93 and EC 1.1.1. . . , respectively), was discovered in cells of Rhodopseudomonas sphaeroides Y, which accounts for the ability of this organism to grow on L-(+)-malate. The enzyme was purified 110-fold to homogeneity with a yield of 51%. During the course of purification, including ion-exchange chromatography and preparative gel electrophoresis, both enzyme activities appeared to be in association. The ratio of their activities remained almost constant [1:10, L-(+)-tartrate dehydrogenase/D-(+)-malate dehydrogenase (decarboxylating)] throughout all steps of purification. Analysis by polyacrylamide gel electrophoresis revealed the presence of a single protein band, the position of which was coincident with both L-(+)-tartrate dehydrogenase and D-(+)-malate dehydrogenase (decarboxylating) activities. The apparent molecular weight of the enzyme was determined to be 158,000 by gel filtration and 162,000 by ultracentrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis yielded a single polypeptide chain with an estimated molecular weight of 38,500, indicating that the enzyme consisted of four subunits of identical size. The isoelectric point of the enzyme was between pH 5.0 and 5.2. The enzyme catalyzed the NAD-linked oxidation of L-(+)-tartrate as well as the oxidative decarboxylation of D-(+)-malate. For both reactions, the optimal pH was in a range from 8.4 to 9.0. The activation energy of the reaction (delta Ho) was 71.8 kJ/mol for L-(+)-tartrate and 54.6 kJ/mol for D-(+)-malate. NAD was required as a cosubstrate, and optimal activity depended on the presence of both Mn2+ and NH4+ ions. The reactions followed Michaelis-Menten kinetics, and the apparent Km values of the individual reactants were determined to be: L-(+)-tartrate, 2.3 X 10(-3) M; NAD, 2.8 X 10(-4) M; and Mn2+, 1.6 X 10(-5) M with respect to L-(+)-tartrate; and D-(+)-malate, 1.7 X 10(-4) M; NAD, 1.3 X 10(-4); and Mn2+, 1.6 X 10(-5) M with respect to D-(+)-malate. Of a variety of compounds tested, only meso-tartrate, oxaloacetate, and dihydroxyfumarate were effective inhibitors. meso-Tartrate and oxaloacetate caused competitive inhibition, whereas dihydroxyfumarate caused noncompetitive inhibition. The Ki values determined for the inhibitors were, in the above sequence, 1.0, 0.014, and 0.06 mM with respect to L-(+)-tartrate and 0.28, 0.012, and 0.027 mM with respect to D-(+)-malate.

Alcohol Oxidoreductases↗
PubMed1998

Mechanism of the protective effect of sodium malate on cisplatin-induced toxicity in mice.

We examined the mechanism of the protective effect of sodium malate on cis-diamminedichloroplatinum(II) (cisplatin, CDDP)-induced nephrotoxicity in mice and obtained the following findings: 1: Sodium malate showed a maximum reduction of toxicity when it was administered at the same time as CDDP or at 30 min before the administration of CDDP; the reduction was significantly decreased when sodium malate was given after the administration of CDDP. 2: It is thought that diamminoplatinum(II) malate (DPM) is produced in the body following the administration of a combination of CDDP and sodium malate. DPM showed the same antitumor effect as CDDP and produced little nephrotoxicity. 3: When CDDP was combined with sodium malate, the time necessary for the elimination of platinum from the blood was prolonged, showing a intermediate value between the times for the elimination of CDDP and DPM from the blood. When the drug clearance was calculated based on this result, it was found that about 40% of the CDDP administered is converted to DPM in the blood. 4: In an experiment using L-[14C] malic acid, it was shown that sodium malate is distributed in the liver and the kidney at high concentrations, but in the tumor at only a low concentration. 5: When sodium malate was administered in combination with CDDP, the amount of platinum which accumulated in the kidney after 24 h was decreased by about 55% compared with the uncombined group, but there was no change in the amount of platinum which accumulated in the tumor. These results suggest that the sodium malate administered may be distributed rapidly in the blood and the tissue, and about 40% is bound to CDDP and converted to DPM, thus reducing the nephrotoxicity of CDDP.

Animals↗
PubMed1997

Malate content of forage varieties commonly fed to cattle.

The objective of this study was to determine the concentration of malate in forage varieties at different stages of maturity. Five alfalfa varieties (Alfagraze, Apollo Supreme Cimarron, Crockett, and Magnum III) and three bermudagrass varieties (Coastal, Tifton-78, and Tifton-85) were collected at different stages of maturity. Samples were collected from replicate plots (n = 3) of each alfalfa variety at 9, 18, 28, 35, and 42 d of maturity; bermudagrass hay samples were composited from six bales of each variety from two cuttings staged to be harvested at 27 and 41 d of maturity. Malate was extracted from the samples and quantitated by high performance liquid chromatography using an organic acid column. As maturity increased, the concentration of malate declined in both plant species. Concentrations of malate were numerically higher in two alfalfa varieties (Crockett and Magnum III) at 35 and 42 d of maturity than in all other alfalfa varieties. Concentrations of malate in bermudagrass at 41 d of maturity were lower than concentrations of malate in all alfalfa varieties at 42 d of maturity. Malate declined as maturity increased in the Coastal and Tifton-78 varieties. Because malate stimulates the utilization of lactate by the predominant ruminal bacterium Selenomonas ruminantium, some of the benefits associated with alfalfa in the diets of dairy cattle may be due to the malate in this forage.

Acidosis↗
PubMed1980

D-Malate dehydrogenase from Pseudomonas fluorescens UK-1.

An enzyme catalyzing oxidative decarboxylation of D-malate was induced by D-malate and beta, beta-dimethyl-malate in Pseudomonas fluorescens UK-1. D-Malate dehydrogenase was purified to homogeneity from the cells grown on D-malate by using ammonium sulfate precipitation, heat treatment, DEAE-sephadex chromatography, Ultrogel AcA 34 gel filtration and 5'-AMP-Sepharose affinity chromatography. D-Malate dehydrogenase has a molecular weight of 140 000 and contains 4 identical subunits of 34 000. The enzyme is very stable against sulfhydryl group reagents or alkylating agents and rather stable against heat or protein denaturants like urea or sodium dodecyl sulfate. NAD protects against heat inactivation and trypsinization but not against protein denaturants. D-Malate dehydrogenase from Escherichia coli does not cross-react with anti-D-malate dehydrogenase to D-malate dehydrogenase form P.fluorescens UK-1.

Immunochemistry↗
PubMed1985

The distribution of inorganic phosphate and malate between intra- and extramitochondrial spaces. Relationship with the transmembrane pH difference.

The steady-state distribution of inorganic phosphate and malate between the intra- and extramitochondrial spaces was measured in suspensions of nonrespiring and respiring rat liver mitochondria in which the transmembrane pH difference was incrementally varied. In respiration-inhibited mitochondria, the slope of log [Pi]in/[Pi]out (ordinate) versus delta pH approached 2 by either chemical or isotopic determination of [Pi], and the slope of log [malate]in/[malate]out versus delta pH was 2.0 with an extrapolated log [Pi]in/[Pi]out value of 0.3 at delta pH = 0. We conclude that the distribution of Pi and malate for nonrespiring mitochondria were quantitatively consistent with those predicted by exchange of Pi- for OH- (or cotransport with H+) and of malate 2- for Pi2-. In respiring mitochondria using glutamate + malate as substrate, there was very little pH dependence of Pi or malate accumulation (the slopes were less than 0.5) unless n-butylmalonate (inhibitor of Pi-dicarboxylate exchange) was added before the glutamate and malate, in which case the distribution patterns at delta pH less than 0.4 were similar to those in nonrespiring mitochondria. In either case, however, after reaching a maximal value of 1.1, log [Pi]in/[Pi]out did not further increase with increasing delta pH. Thus, in normally metabolizing mitochondria, the distributions of Pi and malate are not directly correlated with the difference in pH across the membrane.

Animals↗
PubMed1998

Flux control of the malate valve in leaf cells.

The coupled processes of the chloroplast trans-envelope transport of malate and oxaloacetate and their interconversion as catalyzed by the stromal NADP-linked malate dehydrogenase are quantitatively analyzed by means of a steady-state model. The equation for the NADP-malate dehydrogenase reaction is developed. The empirical dependence of enzyme activity on NADPH and NADP+ is used to determine its actual activity. The trans-envelope counter exchange of malate and oxaloacetate is described by a kinetic model of the translocator. Kinetic parameters are derived from known data, except for the Km value and the maximum rate for oxaloacetate transport, which are estimated from oxaloacetate-dependent malate formation in isolated intact chloroplasts. Using the kinetic properties of the system and the known metabolite concentrations, the model demonstrates that photosynthetically generated NADPH can be exported efficiently from the chloroplasts to the cytosol by the malate-valve system. The transfer capacity of the malate valve is estimated not to exceed 20 mumol (mg Chl)-1 h-1 (or 5% of the electron transport) under normal physiological conditions. The possible role of the malate valve in leaf cells under normal conditions and during stress is discussed.

Chloroplasts↗
PubMed1975

Regulation of oxaloacetate, aspartate, and malate formation in mesophyll protoplast extracts of three types of c(4) plants.

The use of mesophyll protoplast extracts from various C(4) species has provided an effective method for studying light-and substrate-dependent formation of oxaloacetate, malate, and asparate at rates equivalent to whole leaf C(4) photosynthesis. Conditions regulating the formation of the C(4) acids were studied with protoplast extracts from Digitaria sanguinalis, an NADP-malic enzyme C(4) species, Eleusineindica, an NAD-malic enzyme C(4) species, and Urochloa panicoides, a phosphoenolpyruvate (PEP) carboxykinase C(4) species. Light-dependent induction of CO(2) fixation by the mesophyll extracts of all three species was relatively low without addition of exogenous substrates. Pyruvate, alanine and alpha-ketoglutarate, or 3-phosphoglycerate induced high rates of CO(2) fixation in the mesophyll extracts with oxaloacetate, malate, and aspartate being the primary products. In all three species, it appears that pyruvate, alanine, or 3-phosphoglycerate may serve as effective precursors to the formation of PEP for carboxylation through PEP-carboxylase in C(4) mesophyll cells. Induction by pyruvate or alanine and alpha-ketoglutarate was light-dependent, whereas 3-phosphoglycerate-induced CO(2) fixation was not.Several differences between these species representing the three C(4) groups were observed. Substrate induction of CO(2) fixation in mesophyll protoplast extracts of D. sanguinalis gave malate as a major product; only by an apparent exchange reaction with cold aspartate did substantial label appear in aspartate (up to 53% of labeled products). In contrast, aspartate was a major product when alanine and alpha-ketoglutarate served as inducing substrates with E. indica (up to 57%) and U. panicoides (up to 86%). With induction by pyruvate or 3-phosphoglycerate, mesophyll preparations of U. panicoides and E. indica were less effective in forming malate (up to 31% of products) than D. sanguinalis (up to 87% of products). After 2 seconds of whole leaf (14)CO(2) fixation, malate was the major labeled product (57%) with D. sanguinalis, whereas with E. indica and U. panicoides aspartate was the predominant product (73% and 76%, respectively).With mesophyll protoplast extracts of D. sanguinalis, aspartate inhibited CO(2) fixation (about 50% at 0.6 mm), while malate was relatively uninhibitory at comparable concentrations. CO(2) fixation by mesophyll protoplast extracts of E. indica was inhibited by malate (about 50% at 0.6 mm), while aspartate was relatively uninhibitory. With mesophyll preparations of U. panicoides, malate or aspartate (2 mm) caused only slight inhibition of CO(2) fixation. The regulation of aspartate and malate synthesis in C(4) mesophyll cells is discussed relative to initial products of photosynthesis in C(4) species in vivo and species differences in the mechanisms of C(4) photosynthesis.

Journal Article↗
PubMed1980

Malate Oxidation in Plant Mitochondria via Malic Enzyme and the Cyanide-insensitive Electron Transport Pathway.

MALATE OXIDATION IN PLANT MITOCHONDRIA PROCEEDS THROUGH THE ACTIVITIES OF TWO ENZYMES: a malate dehydrogenase and a NAD(+)-dependent malic enzyme. In cauliflower, mitochondria malate oxidation via malate dehydrogenase is rotenone- and cyanide-sensitive. Addition of exogenous NAD(+) stimulates the oxidation of malate via malic enzyme and generates an electron flux that is both rotenone- and cyanide-insensitive. The same effects of exogenous NAD(+) are also observed with highly cyanide-sensitive mitochondria from white potato tubers or with mitochondria from spinach leaves. Both enzymes are located in the matrix, but some experimental data also suggest that part of malate dehydrogenase activity is also present outside the matrix compartment (adsorbed cytosolic malate dehydrogenase?). It is concluded that malic enzyme and a specific pool of NAD(+)/NADH are connected to the cyanide-insensitive alternative pathway by a specific rotenone-insensitive NADH dehydrogenase located on the inner face of the inner membrane. Similarly, malate dehydrogenase and another specific pool of NAD(+)/NADH are connected to the cyanide- (and antimycin-) sensitive pathway by a rotenone-sensitive NADH dehydrogenase located on the inner face of the inner membrane. A general scheme of electron transport in plant mitochondria for the oxidation of malate and NADH can be given, assuming that different pools of ubiquinone act as a branch point between various dehydrogenases, the cyanide-sensitive cytochrome pathway and the cyanide-insensitive alternative pathway.

Journal Article↗
PubMed1998

Two malate dehydrogenases in Methanobacterium thermoautotrophicum.

Methanobacterium thermoautotrophicum (strain Marburg) was found to contain two malate dehydrogenases, which were partially purified and characterized. One was specific for NAD+ and catalyzed the dehydrogenation of malate at approximately one-third of the rate of oxalacetate reduction, and the other could equally well use NAD+ and NADP+ as coenzyme and catalyzed essentially only the reduction of oxalacetate. Via the N-terminal amino acid sequences, the encoding genes were identified in the genome of M. thermoautotrophicum (strain DeltaH). Comparison of the deduced amino acid sequences revealed that the two malate dehydrogenases are phylogenetically only distantly related. The NAD+-specific malate dehydrogenase showed high sequence similarity to L-malate dehydrogenase from Methanothermus fervidus, and the NAD(P)+-using malate dehyrogenase showed high sequence similarity to L-lactate dehydrogenase from Thermotoga maritima and L-malate dehydrogenase from Bacillus subtilis. A function of the two malate dehydrogenases in NADPH:NAD+ transhydrogenation is discussed.

Acetates↗
PubMed1984

Evidence for the role of malic enzyme in the rapid oxidation of malate by cod heart mitochondria.

Mitochondria isolated from the heart of cod (Gadus morrhua callarias) oxidized malate as the only exogenous substrate very rapidly. Pyruvate only slightly increased malate oxidation by these mitochondria. This is in contrast with the mitochondria isolated from rat and rabbit heart which oxidized malate very slowly unless pyruvate was added. Arsenite and hydroxymalonate (an inhibitor of malic enzyme) inhibited the respiration rate of mitochondria isolated from cod heart, when malate was the only exogenous substrate. Inhibition caused by hydroxymalonate was reversed by the addition of pyruvate. In the presence of arsenite, malate was converted to pyruvate by cod heart mitochondria. Cod heart mitochondria incubated in the medium containing Triton X-100 catalyzed the reduction of NADP+ in the presence of L-malate and Mn2+ at relatively high rate (about 160 nmoles NADPH formed/min/mg mitochondrial protein). The oxidative decarboxylation of malate was also taking place when NADP+ was replaced by NAD+ (about 25 nmol NADH formed per min per mg mitochondrial protein). These results suggest that the mitochondria contain both NAD+- and NADP+-linked malic enzymes. These two activities were eluted from DEAE-Sephacel as two independent peaks. It is concluded that malic enzyme activity (presumably both NAD+- and NADP+-linked) is responsible for the rapid oxidation of malate (as the only external substrate) by cod heart mitochondria.

Animals↗
PubMed1970

Properties and regulation of leaf nicotinamide-adenine dinucleotide phosphate-malate dehydrogenase and 'malic' enzyme in plants with the C4-dicarboxylic acid pathway of photosynthesis.

1. NADP-malate dehydrogenase and ;malic' enzyme in maize leaf extracts were separated from NAD-malate dehydrogenase and their properties were examined. 2. The NADP-malate dehydrogenase was nicotinamide nucleotide-specific but otherwise catalysed a reaction comparable with that with the NAD-specific enzyme. By contrast with the latter enzyme, a thiol was absolutely essential for maintaining the activity of the NADP-malate dehydrogenase, and the initial velocity in the direction of malate formation, relative to the reverse direction, was faster. 3. For the ;malic' enzyme reaction the K(m) for malate was dependent on pH and the pH optimum varied with the malate concentration. At their respective optimum concentrations the maximum velocity for this enzyme was higher with Mg(2+) than with Mn(2+). 4. The NADP-malate dehydrogenase in green leaves was rapidly inactivated in the dark and was reactivated when plants were illuminated. Reactivation of the enzyme extracted from darkened leaves was achieved simply by adding a thiol compound. 5. The activity of both enzymes was low in etiolated leaves of maize plants grown in the dark but increased 10-20-fold, together with chlorophyll, when leaves were illuminated. 6. The activity of these enzymes in different species with the C(4)-dicarboxylic acid pathway was compared and their possible role in photosynthesis was considered.

Chlorophyll↗
PubMed2006

The product complex of M. tuberculosis malate synthase revisited.

Enzymes of the glyoxylate shunt have been implicated as virulence factors in several pathogenic organisms, notably Mycobacterium tuberculosis and Candida albicans. Malate synthase has thus emerged as a promising target for design of anti-microbial agents. For this effort, it is essential to have reliable models for enzyme:substrate complexes. A 2.7 Angstroms resolution crystal structure for M. tuberculosis malate synthase in the ternary complex with magnesium, malate, and coenzyme A has been previously described. However, some unusual aspects of malate and Mg(++) binding prompted an independent determination of the structure at 2.3 Angstroms resolution, in the presence of saturating concentrations of malate. The electron density map of the complex reveals the position and conformation of coenzyme A to be unchanged from that found in the previous study. However, the coordination of Mg(++) and orientation of bound malate within the active site are different. The revised position of bound malate is consistent with a reaction mechanism that does not require reorientation of the electrophilic substrate during the catalytic cycle, while the revised Mg(++) coordination is octahedral, as expected. The results should be useful in the design of malate synthase inhibitors.

Coenzyme A↗
PubMed2000

Functions of the membrane-associated and cytoplasmic malate dehydrogenases in the citric acid cycle of Corynebacterium glutamicum.

Like many other bacteria, Corynebacterium glutamicum possesses two types of L-malate dehydrogenase, a membrane-associated malate:quinone oxidoreductase (MQO; EC 1.1.99.16) and a cytoplasmic malate dehydrogenase (MDH; EC 1.1.1.37) The regulation of MDH and of the three membrane-associated dehydrogenases MQO, succinate dehydrogenase (SDH), and NADH dehydrogenase was investigated. MQO, MDH, and SDH activities are regulated coordinately in response to the carbon and energy source for growth. Compared to growth on glucose, these activities are increased during growth on lactate, pyruvate, or acetate, substrates which require high citric acid cycle activity to sustain growth. The simultaneous presence of high activities of both malate dehydrogenases is puzzling. MQO is the most important malate dehydrogenase in the physiology of C. glutamicum. A mutant with a site-directed deletion in the mqo gene does not grow on minimal medium. Growth can be partially restored in this mutant by addition of the vitamin nicotinamide. In contrast, a double mutant lacking MQO and MDH does not grow even in the presence of nicotinamide. Apparently, MDH is able to take over the function of MQO in an mqo mutant, but this requires the presence of nicotinamide in the growth medium. It is shown that addition of nicotinamide leads to a higher intracellular pyridine nucleotide concentration, which probably enables MDH to catalyze malate oxidation. Purified MDH from C. glutamicum catalyzes oxaloacetate reduction much more readily than malate oxidation at physiological pH. In a reconstituted system with isolated membranes and purified MDH, MQO and MDH catalyze the cyclic conversion of malate and oxaloacetate, leading to a net oxidation of NADH. Evidence is presented that this cyclic reaction also takes place in vivo. As yet, no phenotype of an mdh deletion alone was observed, which leaves a physiological function for MDH in C. glutamicum obscure.

Cell Membrane↗
PubMed1997

Succinate and malate improve development of hamster eight-cell embryos in vitro: confirmation of viability by embryo transfer.

The in vitro development of hamster preimplantation embryos is supported by non-glucose energy substrates. To investigate the importance of embryonic metabolism, influence of succinate and malate on the development of hamster 8-cell embryos to blastocysts was examined using a chemically defined protein-free modified hamster embryo culture medium-2 (HECM-2m). There was a dose-dependent influence of succinate on blastocyst development; 0.5 mM succinate was optimal (85.1% +/- 3.9 vs. 54.5% +/- 3.5). In succinate-supplemented HECM-2m, blastocyst development was reduced by omission of lactate (68.5% +/- 7.2), but not pyruvate (85.8% +/- 6.2) or glutamine (84.1% +/- 2.1). Succinate along with either glutamine or lactate or pyruvate poorly supported blastocyst development (28%-58%). Malate also stimulated blastocyst development; 0.01 mM malate was optimal (86.3% +/- 2.8). Supplementation of both succinate and malate to HECM-2m supported maximal (100%) blastocyst development, which was inhibited 4-fold by the addition of glucose/phosphate. The mean cell numbers (MCN) of blastocysts cultured in succinate-supplemented HECM-2m was higher (28.3 +/- 1.1) than it was for those cultured in the absence of glutamine or pyruvate (range 20-24). The MCN was the highest (33.4 +/- 1.6) for blastocysts cultured in succinate-malate-supplemented HECM-2m followed by those in succinate (28.3 +/- 1.1) or malate (24.7 +/- 0.5) supplemented HECM-2m. Embryo transfer experiments showed that 29.8% (+/- 4.5) of transferred blastocysts cultured in succinate-malate-supplemented HECM-2m produced live births, similar (P > 0.1) to the control transfers of freshly recovered 8-cells (33.5% +/- 2.0) or blastocysts (28.9% +/- 3.0). These data show that supplementation of succinate and malate to HECM-2m supports 100% development of hamster 8-cell embryos to high quality viable blastocysts and that non-glucose oxidizable energy substrates are the most preferred components in hamster embryo culture medium.

Animals↗
PubMed1993

Malate-induced feedback regulation of plasma membrane anion channels could provide a CO2 sensor to guard cells.

Plants have developed strategies to circumvent limitations in water supply through the adjustment of stomatal aperture in relation to the photosynthetic capacity (water-use efficiency). The CO2 sensor of guard cells, reporting on the metabolic status of the photosynthetic tissue, is, however, as yet unknown. We elucidated whether extracellular malate has the capability to serve as a signal metabolite in regulating the membrane properties of guard cells. Patch-clamp studies showed that slight variations in the external malate concentration induced major alterations in the voltage-dependent activity of the guard cell anion channel (GCAC1). Superfusion of guard cell protoplasts with malate solutions in the physiological range caused the voltage-gate to shift towards hyperpolarized potentials (Km(mal) = 0.4 mM elicits a 38 mV shift). The selectivity sequence of the anion channel NO3- (4.2) > or = I- (3.9) > Br- (1.9) > Cl- (1) >> mal (0.1) indicates that malate is able to permeate GCAC1. The binding site for shifting the gate is, however, located on the extracellular face of the channel since cytoplasmic malate proved ineffective. Single-channel analysis indicates that extracellular malate affects the voltage-dependent mean open time rather than the unitary conductance of GCAC1. In contrast to malate the rise in the extracellular Cl- concentration increases the unit conductance of the anion efflux channel. We suggest that stomata sense changes in the intercellular CO2 concentration and thus the photosynthetic activity of the mesophyll via feedback regulation of anion efflux from guard cells through malate-sensitive GCAC1.

Anions↗