Showing papers on "Malic enzyme published in 1985"
TL;DR: Rat liver malic enzyme (ME) synthesis is known to be regulated by 3,5,3'-triiodo-L-thyronine (T3).
Abstract: Rat liver malic enzyme (ME) synthesis is known to be regulated by 3,5,3'-triiodo-L-thyronine (T3). Hybridization of 32P-labeled ME cDNA with RNA extracted from normal and T3-induced livers (15 or 50 micrograms/100 g body weight for 10 days) showed an increase in the ME mRNA concentration by approximately 11-fold in T3-treated rats. ME activity and ME mass were stimulated to the same degree as ME mRNA. Northern blot analysis of either total or poly(A+) RNA revealed two distinct ME mRNAs (21 and 27 S) which were equally induced by T3 treatment. Both mRNAs were shown by in vitro translation assay to program the synthesis of the same immunoprecipitable protein corresponding to full-sized ME. From all the above, we concluded that both messages code for active enzyme. ME activity and ME mRNA were also detected in nonhepatic tissues for which different responses to T3 induction were observed without direct correlation with their respective content of T3 nuclear receptor. Increases in ME activity and level of hybridizable ME mRNA were seen 48 h after a single administration of T3 (200 micrograms/100 g body weight) in liver, kidney, and heart (10.3- and 15.5-, 1.7- and 2.6-, and 1.72- and 3.4-fold above basal values, respectively). Lower levels of induction could already be detected after 24 h, liver being the most stimulated tissue. ME was not affected in brain, lung, testis, and spleen. Northern blot analysis showed that both ME mRNAs are present in all tissues tested, although in different relative proportions.(ABSTRACT TRUNCATED AT 250 WORDS)
77 citations
TL;DR: Both increased transcription and decreased degradation contribute to the 20-fold increase in malic enzyme mRNA caused by feeding starved ducklings, which is concluded to be selective.
68 citations
TL;DR: The properties of ATP:citrate lyase, malic enzyme, and AMP deaminase have been investigated in Rhodosporidium toruloides and the role of this enzyme and the central position of malate as a key metabolite in determining how lipid accumulation could be initiated and then sustained is discussed.
Abstract: The properties of ATP:citrate lyase, malic enzyme, and AMP deaminase have been investigated in Rhodosporidium toruloides CBS 14. ATP:citrate lyase had a molecular size of 480 000 daltons and appare...
68 citations
TL;DR: It is proposed that these substances are then transported in the circulatory system of the animals to the bacteria in the trophosome, where malate is decarboxylated and the CO2 released is incorporated in the bacteria.
Abstract: Specimens of the large pogonophoran tube worm Riftia pachyptila were collected at the hydrothermal vents at 21°N on the East Pacific Rise (20°50′ N, 109°06′ W). Incubations of live animals in the presence of radiolabeled CO2 showed an incorporation of radioactivity in the obturacular plume into malate and succinate. It is proposed that these substances are then transported in the circulatory system of the animals to the bacteria in the trophosome, where malate is decarboxylated and the CO2 released is incorporated in the bacteria. A CO2 fixation rate of up to 16 μmol/h−1/g fresh wt−1 could be observed in the obturacular plume. Several carboxylating enzymes were tested; pyruvate carboxylase and malic enzyme (NADP) had an activity of 0.04 U/g fresh wt−1, and phosphoenolpyruvate carboxykinase (GDP) 0.01 U/g fresh wt−1; acetyl CoA carboxylase, malic enzyme (NAD), phosphoenolpyruvate carboxykinase (ADP), and phosphoenolpyruvate carboxylase could not be detected. The quantitative importance of CO2 fixation by s...
60 citations
TL;DR: Malate dehydrogenase (oxaloacetate-decarboxylating) (NADP + ) EC 1.1.40, malic enzyme, has been purified 40-fold to a homogeneous state using affinity chromatography and gel permeation chromatography.
51 citations
TL;DR: The subcellular location and some properties of the rat kidney 25-hydroxyvitamin D3-1 alpha-hydroxylase are described and the enzyme, located in the mitochondria, requires molecular oxygen and a source of NADPH.
44 citations
TL;DR: The studies of whole-leaf respiration establish that mitochondria are implicated in malate degradation in vivo, and an increase in cyanide resistance of the leaf respiration has been observed during the first daylight hours, when malate was oxidized to pyruvate by cytosolic and mitochondrial malic enzymes.
Abstract: Kalanchoe blossfeldiana plants grown under long days (16 h light) exhibit a C3-type photosynthetic metabolism. Switching to short days (9 h light) leads to a gradual development of Crassulacean acid metabolism (CAM). Under the latter conditions, dark CO2 fixation produces large amounts of malate. During the first hours of the day, malate is rapidly decarboxylated into pyruvate through the action of a cytosolic NADP+-or a mitochondrial NAD+-dependent malic enzyme. Mitochondria were isolated from leaves of plants grown under long days or after treatment by an increasing number of short days. Tricarboxylic acid cycle intermediates as well as exogenous NADH and NADPH were readily oxidized by mitochondria isolated from the two types of plants. Glycine, known to be oxidized by C3-plant mitochondria, was still oxidized after CAM establishment. The experiments showed a marked parallelism in the increase of CAM level and the increase in substrate-oxidation capacity of the isolated mitochondria, particularly the capacity to oxidize malate in the presence of cyanide. These simultaneous variations in CAM level and in mitochondrial properties indicate that the mitochondrial NAD+-malic enzyme could account at least for a part of the oxidation of malate. The studies of whole-leaf respiration establish that mitochondria are implicated in malate degradation in vivo. Moreover, an increase in cyanide resistance of the leaf respiration has been observed during the first daylight hours, when malate was oxidized to pyruvate by cytosolic and mitochondrial malic enzymes.
41 citations
TL;DR: It is suggested that, after food intake, the physiological activity of acetyl-CoA carboxylase was increased with the substrate increase and/or with the catalytic activation with citrate, and consequently, the fatty acid synthetase activity was also increased, whereas the enzyme activities measured under optimum conditions were not.
25 citations
TL;DR: There was substantial conversion of (13C-4>)-aspartate to C-1,4 succinate with no detectable enrichment of other compounds under anoxic conditions, suggesting that the malic enzyme may not be functional in the decarboxylating direction under these conditions.
Abstract: Carbon nuclear magnetic resonance (13C-NMR) spectroscopic techniques were used to investigate the metabolism of (13C-3>)-aspartate and (13C-4>)-aspartate by in vitro preparations of the ventricle of the whelk Busycon contrarium. Under anoxic conditions, there was substantial conversion of (13C-4>)-aspartate to C-1,4 succinate with no detectable enrichment of other compounds. When (13C-3>)-aspartate was the substrate, there was substantial enrichment of C-2,3 succinate. However, there was no detectable enrichment of the C-2 or C-3 positions of alanine. This finding suggests that the direct transfer of carbon from aspartate to alanine is minimal under anoxic conditions in whelk ventricle. Thus, the malic enzyme may not be functional in the decarboxylating direction under these conditions.
23 citations
TL;DR: Enzymes of glucose metabolism were assayed in crude cell extracts of Frankia strains HFPArI3 and HFPCcI2 as well as in isolated vesicle clusters from Alnus rubra root nodules, finding similar activities of most enzymes except malic enzyme, which was higher in the cultures grown on the organic acid.
Abstract: Enzymes of glucose metabolism were assayed in crude cell extracts of Frankia strains HFPArI3 and HFPCcI2 as well as in isolated vesicle clusters from Alnus rubra root nodules. Activities of the Embden-Meyerhof-Parnas pathway enzymes glucokinase, phosphofructokinase, and pyruvate kinase were found in Frankia strain HFPArI3 and glucokinase and pyruvate kinase were found in Frankia strain HFPCcI2 and in the vesicle clusters. An NADP+-linked glucose 6-phosphate dehydrogenase and an NAD-linked 6-phosphogluconate dehydrogenase were found in all of the extracts, although the role of these enzymes is unclear. No NADP+-linked 6-phosphogluconate dehydrogenase was found. Both dehydrogenases were inhibited by adenosine 5-triphosphate, and the apparent Km's for glucose 6-phosphate and 6-phosphogluconate were 6.86 X 10(-4) and 7.0 X 10(-5) M, respectively. In addition to the enzymes mentioned above, an NADP+-linked malic enzyme was detected in the pure cultures but not in the vesicle clusters. In contrast, however, the vesicle clusters had activity of an NAD-linked malic enzyme. The possibility that this enzyme resulted from contamination from plant mitochondria trapped in the vesicle clusters could not be discounted. None of the extracts showed activities of the Entner-Doudoroff enzymes or the gluconate metabolism enzymes gluconate dehydrogenase or gluconokinase. Propionate- versus trehalose-grown cultures of strain HFPArI3 showed similar activities of most enzymes except malic enzyme, which was higher in the cultures grown on the organic acid. Nitrogen-fixing cultures of strain HFPArI3 showed higher specific activities of glucose 6-phosphate and 6-phosphogluconate dehydrogenases and phosphofructokinase than ammonia-grown cultures.
22 citations
TL;DR: Findings are consistent with the hypothesis that growth hormone antagonizes the action of agents that stimulate the activity of malic enzyme while concomitantly increasing the extractable activity of glucose-6-phosphate dehydrogenase.
Abstract: The presence of cloned methionyl human growth hormone at 1 microgram/ml medium for the final 5 days of a 6-day culture period decreased the activity of malic enzyme (EC 1.1.1.40) 45% from 202 to 112, fatty acid synthetase 52% from 26 to 12, and ATP citrate lyase (EC 4.1.3.8) 20% from 192 to 154 nmol NADPH.min-1.mg-1 supernatant protein in rat hepatocytes maintained in serum-free primary culture. Also, the activity of mitochondrial glycerol-3-phosphate dehydrogenase (EC 1.1.99.5) decreased 52% from 20 to 9 nmol.min-1.mg-1 mitochondrial protein. In the same cells, no changes were observed in the activity of 6-phosphogluconate dehydrogenase (EC 1.1.1.44) and lactate dehydrogenase (EC 1.1.1.27). Glucose-6-phosphate dehydrogenase (EC 1.1.1.49) was increased 2.4-fold from 70 to 183 nmol.min-1.mg-1 protein, indicating the activity of this enzyme was paradoxically increased, whereas other enzymes involved in lipogenesis were decreased. Half-maximal decrease of malic enzyme activity and increase of glucose-6-phosphate dehydrogenase activity occurred at 10 and 3 ng methionyl human growth hormone per milliliter medium, respectively. These values are within the range of normal circulating growth hormone concentrations in the rat. The effects on malic enzyme and glucose-6-phosphate dehydrogenase appeared after 3-day exposure to growth hormone. These findings are consistent with the hypothesis that growth hormone antagonizes the action of agents that stimulate the activity of malic enzyme while concomitantly increasing the extractable activity of glucose-6-phosphate dehydrogenase.
TL;DR: The purity of the NADPH produced was determined to be 95% from its coenzyme activity with NAD(P)+-linked glutathione reductase, and was purified by ethanol precipitation and dried in vacuo in powdered form with 97% purity.
TL;DR: Mitochondrial-containing particulate fractions from TPC and especially SPC had markedly higher levels of NADP+-dependent malic enzymes than NPC in the presence or absence of pyruvate, suggesting that induction of mitochondrial malic enzyme activity occurs early in the progression of neoplasia.
TL;DR: Ratios of end-products and calculations of approximate redox balance suggest that the Toronto strain may have a greater capacity for aerobic metabolism.
TL;DR: The results suggest that insulin regulates the accumulation of mRNAs encoding these two inducible proteins in an asynchronous manner directly related to the metabolic requirements of the animal.
TL;DR: Mitochondria isolated from the heart of the Baltic salmon trout Salmo trutta contain two distinct malic enzymes (NAD-preferring malic enzyme) that catalyses the oxidative decarboxylation of malate in the presence of either NAD or NADP.
Abstract: 1. 1. Mitochondria isolated from the heart of the Baltic salmon trout Salmo trutta contain two distinct malic enzymes. 2. 2. One of these enzymes (NAD-preferring malic enzyme) catalyses the oxidative decarboxylation of malate in the presence of either NAD or NADP. The specific activity with NAD was six times that with NADP as coenzyme. The second enzyme is specific for NADP. 3. 3. These two malic enzymes have been separated by: ion exchange chromatography of DEAE-Sephacel, affinity chromatography on 2′,5′ADP-Sepharose 4B, gel filtration on Sephacryl S-300 and polyacrylamide gel electrophoresis. 4. 4. The mol. wts of the two native malic enzymes determined by gel filtration were found to be 280,000 and 190,000 for NAD-preferring and NADP-specific malic enzyme, respectively. 5. 5. Chromatofocusing revealed the isoelectric points of the two enzymes at pH 5.45 and 5.85 for NAD-preferring and NADP-specific malic enzyme, respectively.
TL;DR: It is concluded that malic enzyme is not specifically linked to the rotenone-insensitive pathway of electron transport, which has important implications for the regulation of energy metabolism in plants.
Abstract: Our aim was to determine whether there is a specific link between NAD-malic enzyme and the rotenone- insensitive bypass of electron transport. Mitochondria were isolated from fresh beetroot tissue, aged beetroot slices, and turnips. Oxygen uptake and pyruvate production were measured in reactions where these mitochondria were metabolizing malate at pH 6.8 in the presence of glutamate, to facilitate the removal of oxaloacetate, and in its absence. In the absence of glutamate there was substantial activity of malic enzyme. NAD+ (577 µM) prevented a fall in oxygen uptake by stimulating malic enzyme. Rotenone (19 µM) reduced oxygen uptake. This inhibited rate was stimulated by NAD+ due, in particular, to a stimulation of malic enzyme. We conclude that the stimulation of malate metabolism by NAD+ is accounted for by malic enzyme due to the unfavourable equilibrium of malate dehydrogenase for malate oxidation and the resultant accumulation of oxaloacetate, and not to any specific link between malic enzyme and the rotenone-insensitive bypass. In the presence of glutamate, malate dehydrogenase was the predominant malate metabolizing enzyme. Oxygen uptake and malic enzyme were stimulated and inhibited by NAD+ and rotenone, respectively. In the presence of rotenone, NAD+ stimulated oxygen uptake and increased the percentage due to malic enzyme. This stimulation is accounted for by the higher Kin of the rotenone-insensitive dehydrogenase for NADH and the unfavourable equilibrium position of malate dehydrogenase resulting in activation of malic enzyme only. We conclude that malic enzyme is not specifically linked to the rotenone-insensitive pathway of electron transport. This has important implications for the regulation of energy metabolism in plants.
TL;DR: The steady-state product-inhibition patterns for pyruvate and NADH indicate a sequential binding of the substrates: NAD+ followed by L-malate, which indicates that NADH is the last product released.
Abstract: The mitochondrial NAD(P)+ malic enzyme [EC 1.1.1.39, L-malate:NAD+ oxidoreductase (decarboxylating)] was purified from rabbit heart to a specific activity of 7 units (mumol/min)/mg at 23 degrees C. A study of the reductive carboxylation reaction indicates that this enzymic reaction is reversible. The rate of the reductive carboxylation reaction appears to be completely inhibited at an NADH concentration of 0.92 mM. A substrate saturation curve of this reaction with NADH as the varied substrate describes this inhibition. The apparent kinetic parameters for this reaction are Ka(NADH) = 239 microM and Vr = 1.1 mumol/min per mg at 23 degrees C. The steady-state product-inhibition patterns for pyruvate and NADH indicate a sequential binding of the substrates: NAD+ followed by L-malate. These data also indicate that NADH is the last product released. A steady-state kinetic model is proposed that incorporates NADH-enzyme dead-end complexes.
TL;DR: In this paper, experiments were carried out on L-malic acid decarboxylation catalyzed by malic enzyme (E.C.1.40) immobilized using three different techniques.
TL;DR: Mitochondrial and cytosolic malic enzymes were assayed radiochemically in fibroblasts from six patients suffering from Friedreich's ataxia in order to verify earlier reports of abnormalities in these enzymes.
Abstract: Mitochondrial and cytosolic malic enzymes were assayed radiochemically in fibroblasts from six patients suffering from Friedreich's ataxia in order to verify earlier reports of abnormalities in these enzymes. No abnormalities could be detected in the activities of either enzyme. On cellulose acetate electrophoresis a band of enzyme activity corresponding to the mitochondrial isoenzyme was detectable contrary to earlier reports. Possible explanations for the disparity of results between different laboratories are discussed.
TL;DR: In the adipose tissues, the specific activities of the three enzymes rather closely followed fluctuations in the rate of fatty acid synthesis, and ACX and especially ME activities were satisfactory indicators of de noovo lipogenesis; G-6-PD activity did not depend on de novo lipogenesis.
Abstract: Changes in the specific activities of acetyl-CoA-carboxylase (ACX), malic enzyme (ME) and glucose-6-phosphate dehydrogenase (G-6-PD) were compared to changes in de novo lipogenesis measured by in vivo incorporation of [3H] of tritiated water into fatty acids of liver and of perirenal and dorsal subcutaneous adipose tissues. In the adipose tissues, the specific activities of the three enzymes rather closely followed fluctuations in the rate of fatty acid synthesis. In the liver, ACX and especially ME activities were satisfactory indicators of de novo lipogenesis; G-6-PD activity did not depend on de novo lipogenesis.
TL;DR: The locus for the mitochondrial malic enzyme (ME2) seems to be closely linked to the gene coding for the A subunit of coagulation factor XIII (F13A), since the assignment of F13A to the short arm of chromosome 6 was recently confirmed.
Abstract: The locus for the mitochondrial malic enzyme (ME2) seems to be closely linked to the gene coding for the A subunit of coagulation factor XIII (F13A). From 18 informative families with 54 children a maximum lod score of 4.33 was obtained at a recombination fraction of 0.10. Since the assignment of F13A to the short arm of chromosome 6 was recently confirmed, the locus for ME2 can be added to this linkage group. The map order seems to be: GLO1-HLA-F13A-ME2.
TL;DR: Property of partially purified NADP-malic enzyme (EC 1.1.40) from glumes of developing wheat grains were examined and activity of malic enzyme was inhibited by products of the reaction viz pyruvate, HCO 3 − and NADPH 2 .
TL;DR: It has been shown that the stimulation by malate of progesterone biosynthesis depends not only on the generation of NADPH by NAD(P)-linked malic enzyme, but also on NADPH formed during further metabolism of pyruvate to isocitrate which is in turn efficiently oxidized by NADP+-linked isOCitrate dehydrogenase.
TL;DR: The maximum velocity of the malic enzyme (L-malate: NADP+ oxidoreductase (oxaloacetate-decarboxylating) and reductive carboxylation of pyruvate and V/KCO2 are pH-independent from pH 5.5 to pH 8.5, suggesting that the protonation state of enzyme is optimum in the malate oxidative decar boxylation direction.
TL;DR: Within each species, although there was considerable variation in the absolute activities of these enzymes, the relative activities were similar to those observed for, or previously published for mammary homogenates.
Abstract: The activities of glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, malic enzyme, lactate dehydrogenase and malate dehydrogenase have been determined in secreted milk from sows, rats and rabbits. Within each species, although there was considerable variation in the absolute activities of these enzymes, the relative activities were similar to those observed for, or previously published for mammary homogenates. The only exception was milk glucose 6-phosphate dehydrogenase which tended to lose activity upon prolonged storage in the mammary gland. These results suggest that the pattern of milk enzymes can be an accurate reflection of that occurring in the mammary gland.
TL;DR: Two revertants were obtained which were derived by back mutation on the ace-7 gene and produce qualitatively different G6PDH from the wild type enzyme, suggesting that the Ace7 gene is a structural gene for G6 PDH, in addition to the three structural genes proposed by Scott and Tatum (1970).
Abstract: Both of the two ace-7 strains of Neurospora crassa isolated in this laboratory lack the activity of glucose-6-phosphate dehydrogenase (G6PDH). In starvation culture for acetate, mycelium of ace-7 shows decreased level of NADPH as compared with that of other acetate mutant does. Two NADPH-forming enzymes, malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+) (so called NADP-linked malic enzyme) and isocitrate dehydrogenase (NADP+), are induced by acetate added in culture medium. Acetate seems to make the ace-7 strain grow because it increases the concentration of NADPH by inducing NADPH-forming malic enzyme and isocitrate dehydrogenase. From ace-7 strains, two revertants were obtained which were derived by back mutation on the ace-7 gene and produce qualitatively different G6PDH from the wild type enzyme. This suggests that the ace-7 gene is a structural gene for G6PDH, in addition to the three structural genes proposed by Scott and Tatum (1970).
TL;DR: The immunoaffinity columns made with each monospecific IgG were able to bind each of the enzymes it immunotitrated and were used to purify partially both isocitrate dehydrogenase and dihydrofolate reductase from crude rat liver homogenate.
Abstract: Monospecific (affinity-purified) anti-(yeast glucose-6-phosphate dehydrogenase) IgG inhibits three different NADPH-requiring enzymes, chicken liver dihydrofolate reductase, pigeon liver fatty acid synthetase and chicken liver malic enzyme. The inhibition of all three enzymes was approx. 50% in a 2h incubation with 100 micrograms of IgG. Similarly, with several different NADH-requiring enzymes, an immunocrossreactivity was observed. Monospecific anti-(rabbit muscle glyceraldehyde-3-phosphate dehydrogenase) IgG inhibited yeast alcohol dehydrogenase and pig heart malate dehydrogenase by 39% and 55% respectively. The cross-reactivity observed was tested by affinity chromatography. Immunoaffinity columns made with each monospecific IgG were able to bind each of the enzymes it immunotitrated. Enzymes were eluted with a nondenaturing solvent with little loss of activity. The immunoaffinity column with monospecific anti-(glucose-6-phosphate dehydrogenase) IgG as the bound ligand was also used to purify partially (over 150-fold) both isocitrate dehydrogenase and dihydrofolate reductase from crude rat liver homogenate.
TL;DR: Electrophoretic banding patterns of eight enzyme systems in Solenopsis xyloni, S. germinata and their hybrid were studied and repression of paternal alleles was found in aldehyde oxidase, isocitrate dehydrogenase, leucine amino peptidase and malic enzyme.
TL;DR: A revision of the taxonomy of the genus Daphnia in southeastern Australia and a finding that obligate asexuality in Daphia cephalata King is a requirement for parthenogenesis.
Abstract: AGAR, W. E. 1920. The genetics of a Daphnia hybrid during parthenogenesis. J. Genet. 10:303330. BROOKS, J. L. 1957. The systematics of North American Daphnia. Mem. Conn. Acad. Arts and Sci. 13:1-180. EINSLE, U. 1966. Einige Beobachtungen und Hypothesen zur Taxonomie der Gattung Daphnia. Schr. Reihe. V.G. Bodensee 84:1-17. ---. 1978. Qualitative und quantitative Anderungen im Crustaceen plankton des Bodensee-Obersees. Arch. Hydrobiol. 32:300-315. HEBERT, P. D. N. 1977a. A revision of the taxonomy of the genus Daphnia in southeastern Australia. Aust. J. Zool. 25:371-398. ---. 1977b. Niche overlap among species in the Daphnia carinata complex. J. Anim. Ecol. 46:399-409. ---. 1978. Cyclomorphosis in natural populations of Daphnia cephalata King. Freshwat. BioI. 8:79-90. --. 1981. Obligate asexuality in Daphnia. Amer. Natur. 117:784-789.