Effect of triiodothyronine and thyroxine on malic enzyme activity and protein and nucleic acid contents of liver and muscle of toad, Bufo melanostictus.
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Animals↗
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Kinetics of Malic Dehydrogenase Inhibition by 2,4-Dichlorophenoxyacetic Acid.
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Journal Article↗
The inhibition of fumarase and malic dehydrogenase by DL-beta-fluoromalic acid.
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Fumarate Hydratase↗
Role of organic acids in enhancing the desorption and uptake of weathered p,p'-DDE by Cucurbita pepo.
Experiments were conducted to assess the effect of seven organic acids [succinic, tartaric, malic, malonic, oxalic, citric, ethylene-diaminetetraacetic (EDTA)] over a concentration range of two orders of magnitude (0.001-0.10 M) on the abiotic desorption of weathered p,p'-DDE and the extraction of polyvalent inorganic ions from soil. At 0.05 M all organic acids significantly increased contaminant desorption by 19-80%. Organic acids also increased the aqueous concentration of eight inorganic constituents extracted from soil, with at least a six-fold increase in the release of Al, Fe, Mn, and P at 0.001 M. Zucchini seedlings grown for 28 d in soil containing weathered p,p'-DDE (300 ng/g, dry weight) were periodically amended with distilled water, citric or oxalic acids (0.01 M). Plants receiving water removed 1.7% of the p,p'-DDE from the soil. Seedlings amended with citric or oxalic acids removed 2.1 and 1.9% of the contaminant, respectively, and contained up to 66% more contaminant in the shoot system than unamended vegetation. A second crop of untreated (distilled water) zucchini in the same soil removed more contaminant than the first crop (2.5%), although the addition of organic acids did not further enhance contaminant uptake. The data indicate that the addition of low molecular weight organic acids causes the partial dissolution of the soil structure through the chelation of inorganic structural ions, potentially enhancing bioavailability and having implications for the phytoremediation of persistent organic pollutants in soil.
Acids↗
Aluminum tolerance of two wheat cultivars (Brevor and Atlas66) in relation to their rhizosphere pH and organic acids exuded from roots.
Phytotoxicity of aluminum (Al) has become a serious problem in inhibiting plant growth on acid soils. Under Al stress, the changes of rhizosphere pH, root elongation, absorption of Al by wheat roots, organic acids exuded from roots, and some main factors related to Al-tolerant mechanisms have been studied using hydroponics, fluorescence spectrophotometry, and high performance liquid chromatography (HPLC). Two wheat cultivars, Brevor and Atlas66, differing in Al tolerance are chosen in the study. Accordingly, the rhizosphere pH has a positive effect on Al tolerance. Atlas66 (Al-tolerant) has higher capability to maintain high rhizosphere pH than Brevor (Al-sensitive) does. High pH can reduce Al3+ activity and toxicity, and increase the efficiency of exuding organic acids from the roots. More inhibition of root elongation has been found in Brevor because of the exposure of roots to Al3+ solution at low pH. Brevor accumulate more Al in roots than Atlas66 even at higher pH. Al-induced exudation of malic and citric acids has been found in Atlas66 roots, while no Al-induced organic acids have been found in Brevor. These results indicate that the Al-induced secretion of organic acids from Atlas66 roots has a positive correlation with Al tolerance. Comprehensive treatment of Al3+ and H+ indicates that wheat is adversely influenced by excess Al3+, rather than low pH.
Aluminum↗
Lipogenic enzyme activities in primary cultures of adult mouse hepatocytes.
The effects of various unsaturated fatty acids such as oleic (18:1n-9), linoleic (18:2n-6) and arachidonic (20:4n-6) on the activities of fatty acid synthetase (FAS), malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) all were determined in primary cultures of mouse hepatocytes. Activities of FAS and ME were found to decrease with time in culture regardless of whether hepatocyte donors were fed diets containing polyunsaturated fatty acid-free hydrogenated cottonseed oil (HCTO) or corn oil (CO). On the other hand, while G6PDH activity also declined in cultured hepatocytes obtained from HCTO-fed mice, the activity of this enzyme increased in cells cultured from CO-fed mice. 6PGDH activity was found to increase in hepatocytes obtained from both diet groups. Neither 18:2 nor 20:4 when added to media could alter FAS or ME activities compared with those observed with either 18:1-containing or fatty acid-free media. Since lactic dehydrogenase activity and the rate of incorporation of [3H] leucine into FAS protein were unaltered with time in hepatocyte cultures, the decreased activities of FAS and ME cannot be attributed to a loss in cell viability during culture but rather appear to be specific for those enzymes which respond to diet hormones in vivo.
Animals↗
Alternative substrates for malic enzyme: oxidative decarboxylation of L-aspartate.
The NAD-malic enzyme from Ascaris suum will utilize L-aspartate, (2S,3R)-tartrate, and meso-tartrate as substrates with V/K values 10(-4)-10(-5) with respect to malate. There is a strict requirement for the 2S stereochemistry for all of these reactants. Since aspartate is unique as an amino acid reactant for malic enzyme, it was informative to determine the details of its mechanism of oxidative decarboxylation. The initial rate of NADH appearance is directly proportional to the concentration of aspartate, and saturation is difficult to achieve. The pH dependence of V/K(aspartate)E(t) shows a decrease at low pH, giving a pK of 5.7. The pH-independent value of V/K(aspartate)E(t) is 3 M(-1) s(-1), 12500-fold lower than that obtained with L-malate. The dissociation constant for aspartate as a competitive inhibitor of malate is 60 mM at neutral pH, allowing an estimate of about 0.18 s(-1) for V/E(t) with L-aspartate compared to a value of 39 s(-1) obtained with L-malate. The deuterium isotope effect on V/K(aspartate) is pH independent over the range 5.1-6.9 with an average value of 3.3. Data suggest that the monoanion of L-aspartate binds to enzyme and that the same general base, general acid mechanism that is responsible for the oxidative decarboxylation of malate to pyruvate applies to the oxidative decarboxylation of aspartate to iminopyruvate. In addition, the oxidation step appears to be largely rate determining with aspartate as the substrate.
Animals↗
Microbial colonization of naturally black olives during fermentation and associated biochemical activities in the cover brine.
AIMS: To establish the site of microbial growth on naturally black fermented table olives, and to monitor the population dynamics of yeasts and selected micro-organisms together with the changes in organic acid profile and pH in the cover brine during fermentation. METHODS AND RESULTS: During fermentation, the numbers of Enterobacteriaceae and Pseudomonas spp. in the brine decreased whilst lactic acid bacteria and yeast populations increased. Scanning electron microscopy showed that a yeast-rich biofilm developed on the epicuticular wax of the olive skin during fermentation. Yeasts also predominated in the stomatal openings, but bacteria were more numerous in intercellular spaces in the sub-stomatal flesh. Citric, malic and tartaric acids were the major organic acids accumulating in the brine during fermentation. CONCLUSIONS: Micro-organisms associated with the skin, stomata and flesh in fermenting black olives may experience different local conditions to those prevailing in the cover brine. SIGNIFICANCE AND IMPACT OF THE STUDY: These are the first observations of the micro-organisms associated with the fruit of naturally fermented black olives and of the accumulation of specific organic acids during fermentation.
Biofilms↗
Heat resistance of Alicyclobacillus acidoterrestris spores as affected by various pH values and organic acids.
Alicyclobacillus acidoterrestris, a thermoacidophilic sporeformer, has caused spoilage of fruit juices which had been treated with thermal processes intended to commercially sterilize the juice. The objective of this research was to document the effect of pH, acid, and temperature on the heat resistance of spores of three fruit-juice isolates of A. acidoterrestris. The thermal resistance of spores of A. acidoterrestris strains VF, WAC, and IP were studied in a model fruit-juice system composed of 12% glucose and 30 mM of either citric, malic, or tartaric acid, adjusted to selected pH values ranging from 2.8 to 4.0. Decimal reduction times (D values) and inactivation rates were determined. Spores of strains VF and WAC were similarly resistant to heat under acidic conditions, while strain IP spores were less resistant. In the range of pH 2.8 to 4.0, a statistically effect of hydrogen ion concentration on heat resistance was observed at lower temperatures, but not at the higher temperatures, but not at the higher temperatures. For examples, at 91 degrees C and pH 3.1 and 3.7, D values were 31.3 and 54.3 min, respectively, while at 97 degrees C D values at pH 3.1 and 3.7 were 7.9 and 8.8 min, respectively. The type of acid did not significantly affect the heat resistance. The zd values ranged from 5.9 to 10 degrees C, depending on the acid, pH, and the strain. The models generated from this research can be used to determine adequate thermal processes, accounting for the acid type, pH, and temperature, to destroy A. acidoterrestris spores in beverages, since this organism is able to survive the typical hot-fill and hold process (2 min at 88 to 96 degrees C) currently used to process fruit juice.
Bacillaceae↗
Cyclic AMP-mediated control of lipogenic enzyme synthesis during adipose differentiation of 3T3 cells.
During the adipose differentiation of 3T3-F442A cells, there is an increase in the synthesis of numerous proteins, including the lipogenic enzymes glycerophosphate dehydrogenase, fatty acid synthetase and malic enzyme. Agents that increase cAMP content (Dibutyryl cAMP, theophylline, and isoproterenol) are known to induce lipolysis in fat cells; but the same agents are shown here to reduce the synthesis of the lipogenic enzymes during adipose differentiation. The extent of reduction depends on the agent used and differs for the three enzymes; fatty acid synthetase is most sensitive and its synthesis can be suppressed completely. In contrast to their effects on lipogenic enzyme synthesis, these agents do not affect morphological changes or the synthesis of several other proteins, of which some increase and others (such as actin) decrease during the differentiation. The effects of the agents on the synthesis of lipogenic enzymes are not dependent on lipolysis, since they take place to the same degree in cells not permitted to accumulate triglyceride. Translation in vitro of mRNA isolated from cells treated with the agents promoting cAMP accumulation indicates that the levels of functional mRNA for lipogenic enzymes are reduced. We conclude that, in addition to its activation of lipolysis, cAMP reduces specifically mRNA accumulation for lipogenic enzymes. These results also demonstrate the independent control of morphological change and enzyme synthesis during adipose differentiation.
Adipose Tissue↗
Identification, isolation, and characterization of cysteinate and thiolactate complexes of bismuth.
Although bismuth compounds have been used in medicine for over 200 years, chemical characterization of complexes involving biological molecules is minimal and mechanisms of bioactivity are ill-defined. The thiophilic nature of bismuth implicates sulfur centers as likely sites for interaction, and we have exploited this feature to identify, isolate, and characterize complexes of bismuth with thiolate-carboxylate bifunctional ligands including the amino acid l-cysteine. The solid-state structures of potassium dichloro(thiopropionato)bismuth (K[1d]), dimethylaminoethanethiolato(thiopropionato)bismuth (4), and dinitrato(cysteinato)bismuthphenanthroline [5(phen)] are compared with data from electrospray ionization mass spectrometry (ESI-MS). ESI-MS is applied to reactions of BiCl(3) or Bi(NO(3))(3) with mercaptosuccinic, malic, and succinic acids to illustrate the general observation of 1:1 and 1:2 complexes.
Bismuth↗
Diurnal changes in chlorophyll a fluorescence, CO(2)-exchange and organic acid decarboxylation in the tropical CAM tree Clusia hilariana.
Crassulacean acid metabolism (CAM) plants are dependent on the organic acids that accumulate overnight in the vacuoles as a source of CO(2) during the daylight deacidification period, when stomata are closed and high irradiances generally prevail. We performed an integrative analysis of diurnal changes in gas exchange, chlorophyll fluorescence parameters and organic acid decarboxylation to understand the adjustments in photochemical and non-photochemical processes during the different CAM phases in Clusia hilariana Schlecht., a dominant tree species in the sandy coastal plains of southeastern Brazil. A linear relationship was obtained between the quantum yields of photochemical and non-photochemical quenching, irrespective of the CAM phase and prevailing irradiance. Degradation of malic and citric acids during the midday stomatal closure period could lead to potential CO(2) fixation rates of 23 &mgr;mol m(-2) s(-1), whereas CO(2) losses, measured as CO(2) evolution, corresponded to about 3% of this value. Thus, decarboxylation of malate and citrate provided high internal CO(2) concentrations during phase III of CAM, even though the stomata were closed, allowing optimal utilization of light energy, as indicated by the non-saturating electron transport rates (ETR) in the light response curves, with highest rates of ETR occurring at midday in the diurnal curves. At the transition from phase III to IV of CAM, depletion of internal CO(2) sources and low stomatal conductances, which restricted the supply of exogenous CO(2), reduced the demand for photochemical energy to drive carbon assimilation. This was compensated by increases in thermal energy dissipation as indicated by higher rates of non-photochemical quenching, while high irradiances still prevailed. Shifts in the CAM phases and changes in protective thermal dissipation potential allowed C. hilariana to match changes in PPFD patterns for leaves of different orientations. Evidence that most of the decline in photochemical efficiency was probably related to the fast-relaxing component of non-photochemical quenching is provided by the high values of the quantum yield of photosystem II after 20 min of relaxation in darkness, and an almost complete recovery after sunset. These adjustments in photosynthetic machinery minimized the danger of photo-inhibition in C. hilariana, which is commonly found in fully exposed habitats.
Journal Article↗
Differences between mouse and rat pancreatic islets: succinate responsiveness, malic enzyme, and anaplerosis.
Succinic acid methyl esters are potent insulin secretagogues in rat pancreatic islets, but they do not stimulate insulin release in mouse islets. Unlike rat and human islets, mouse islets lack malic enzyme and, therefore, are unable to form pyruvate from succinate-derived malate for net synthesis of acetyl-CoA. Dimethyl-[2,3-(14)C]succinate is metabolized in the citric acid cycle in mouse islets to the same extent as in rat islets, indicating that endogenous acetyl-CoA condenses with oxaloacetate derived from succinate. However, without malic enzyme, the net synthesis from succinate of the citric acid cycle intermediates citrate, isocitrate, and alpha-ketoglutarate cannot occur. Glucose and other nutrients that augment alpha-ketoglutarate formation are secretagogues in mouse islets with potencies similar to those in rat islets. All cycle intermediates can be net-synthesized from alpha-ketoglutarate. Rotenone, an inhibitor of site I of the electron transport chain, inhibits methyl succinate-induced insulin release in rat islets even though succinate oxidation forms ATP at sites II and III of the respiratory chain. Thus generating ATP, NADH, and anaplerosis of succinyl-CoA plus the four-carbon dicarboxylic acids of the cycle and its metabolism in the citric acid cycle is insufficient for a fuel to be insulinotropic; it must additionally promote anaplerosis of alpha-ketoglutarate or two intermediates interconvertible with alpha-ketoglutarate, citrate, and isocitrate.
Animals↗
Carbon-flux distribution in the central metabolic pathways of Corynebacterium glutamicum during growth on fructose.
Growth of Corynebacterium glutamicum on fructose was significantly less than that obtained on glucose, despite similar rates of substrate uptake. This was in part due to the production of overflow metabolites (dihydroxyacetone and lactate) but also to the increased production of CO2 during growth on fructose. These differences in carbon-metabolite accumulation are indicative of a different pattern of carbon-flux distribution through the central metabolic pathways. Growth on glucose has been previously shown to involve a high flux (> 50% of total glucose consumption) via the pentose pathway to generate anabolic reducing equivalents. NMR analysis of carbon-isotope distribution patterns of the glutamate pool after growth on 1-13C- or 6-13C-enriched fructose indicates that the contribution of the pentose pathway is significantly diminished during exponential growth on fructose with glycolysis being the predominant pathway (80% of total fructose consumption). The increased flux through glycolysis during growth on fructose is associated with an increased NADH/NAD+ ratio susceptible to inhibit both glyceraldehyde-3-phosphate dehydrogenase and pyruvate dehydrogenase, and provoking the overflow of metabolites derived from the substrates of these two enzymes. The biomass yield observed experimentally is higher than can be estimated from the apparent quantity of NADPH associated with the pentose pathway and the flux through isocitrate dehydrogenase, suggesting an additional reaction yielding NADPH. This may involve a modified tricarboxylic acid cycle involving malic enzyme, expressed to significantly higher levels during growth on fructose than on glucose, and a pyruvate carboxylating anaplerotic enzyme.
Biological Transport↗
Influence of harvest date within the season and cold storage on cherimoya fruit ripening.
Cherimoya ripening with and without prior storage at 8 degrees C was studied in fruit harvested on early- (EH), mid- (MH), and late-season (LH) dates. Most of the differences in the ripening behavior were observed between EH cherimoyas and fruit from the other two harvest dates. During ripening of nonstored fruit, the increases in ethylene production and respiration rates and in soluble sugars and organic acids contents were faster in EH than in the other fruits (which ripened 1 day later). These differences could be due to variations in the physiological stage at harvest as a result of the different heat units (degree/month) accumulated in the last month of fruit development. During ripening of cold-stored fruit the differences in the time to the onset of the increase in ethylene production and in the accumulation of malic and citric acid were minimized, especially after longer storage times, and the relationship of harvest date with the increases in respiration rate was lost. Glucose and fructose accumulation was reduced by prior cold storage, especially after longer storage duration and in MH and LH fruit, but sucrose hydrolysis was almost complete, as in nonstored fruit. It is suggested that glucose and fructose accumulation is more sensitive to low temperature than sucrose metabolism and that this differential sensitivity is more marked in MH and LH cherimoyas. The time to ripen was inversely related to prior cold storage duration and was dependent on harvest date: the later the harvest date, the longer storage time it took to shorten subsequent ripening.
Cold Temperature↗
Effects of androgens, prolactin and bromocriptine on seminal vesicular enzymes of the pyruvate malate cycle involved in lipogenesis in castrated mature monkeys, Macaca radiata.
The interaction of androgens and prolactin, the major factors regulating the male accessory sex organs, on the specific activity of seminal vesicular enzymes of the pyruvate/malate cycle were studied in castrated mature monkeys. Castration decreased the activity of these enzymes, including NADP+ isocitrate dehydrogenase, ATP citrate lyase, malate dehydrogenase, malic enzyme and fatty acid synthase. Testosterone propionate (TP)/dihydrotestosterone given as replacement to castrates increased the activity of all these enzymes, except for malate dehydrogenase. Prolactin restored normal activity of ATP citrate lyase, malic enzyme and fatty acid synthase but not of isocitrate dehydrogenase and malate dehydrogenase (MDH). Prolactin had a specific control over MDH. Moreover, when prolactin was combined with androgens a further stimulatory influence was observed on fatty acid synthase activity. In order to prove the direct influence of prolactin on enzymes of the pyruvate/malate cycle, bromocriptine was administered and this inhibited all of the enzymes. Thus prolactin was found to have a direct, as well as a synergistic, action with androgens on enzymes of the pyruvate/malate cycle in the seminal vesicles of monkeys.
ATP Citrate (pro-S)-Lyase↗
Dietary phospholipid-dependent reductions in gene expression and activity of liver enzymes in fatty acid synthesis in fasted-refed rats.
The effects of dietary soybean phospholipid, its hydrogenation product and safflower phospholipid on gene expression and the activity of hepatic enzymes in fatty acid biosynthesis were examined in fasted-refed rats. Phospholipid composition of soybean phospholipid and its hydrogenation product were the same, but the hydrogenation product contained negligible amounts of unsaturated fatty acids. Among phospholipid classes, lysophosphatidylcholine and phosphatidylinositol proportions were slightly higher in safflower phospholipid than in soybean phospholipid or its hydrogenation product. Rats were fasted for 2 d and refed a fat-free diet or a diet containing 4% fatty acids either as soybean oil or various phospholipid preparations for 3 d. Compared to the fat-free diet, the soybean oil diet only slightly decreased specific, but not total hepatic fatty acid synthetase and malic enzyme activity, and it was totally ineffective in modulating glucose 6-phosphate dehydrogenase and pyruvate kinase activity under our experimental conditions. The diets containing phospholipids, however, markedly decreased the activity of these enzymes. The extent of reduction was somewhat attenuated with hydrogenated soybean phospholipid as compared with soybean and safflower phospholipids. Dot and Northern blot hybridization using specific cDNA probes showed that, compared to a fat-free diet, diets containing phospholipids profoundly decreased the hepatic mRNA levels of enzymes in fatty acid synthesis. Soybean oil, however, only marginally affected these parameters. Hepatic mRNA levels for enzymes correlated well with enzyme activity. Dietary phospholipids therefore appear to have decreased enzyme activity in fatty acid synthesis primarily by suppressing the mRNA levels of these enzymes. Compared to soybean oil, hydrogenated soybean phospholipid is still effective in decreasing the activity and mRNA level of enzymes in fatty acid synthesis. Therefore, it is difficult to ascribe the potent physiological activity of phospholipid in reducing fatty acid synthesis entirely to polyunsaturated fatty acid moiety.
Animals↗
Chemosensory properties of sour tastants.
In Experiment 1, a taste quality fractionation procedure was used to establish the degree to which sour and non-sour taste sensations are elicited by six concentrations of each of seven acids: citric, hydrochloric, sulfuric, lactic, malic, phosphoric and tartaric. In general, the acids differed significantly in their ability to elicit sour, salty and bitter sensations, with sulfuric and hydrochloric acids producing the smallest proportions of perceived sourness. Bitterness was found to be the largest non-sour sensation produced, followed by saltiness. The perceived taste qualities of the acids were stable across a wide range of concentrations. In Experiment 2 the extent to which the vapors of these test acids produce detectable intranasal non-gustatory sensations at concentration levels used in many human taste experiments was examined. All acids induced clear intranasal sensations at concentration levels used in some suprathreshold taste paradigms. The results suggest that a number of measures of sour taste sensation may be confounded by non-sour chemosensory factors, including intranasal stimulation.
Acids↗