Showing papers on "Malic enzyme published in 1991"
TL;DR: Comparison of the amino acid sequence of the human protein with the published NADP(+)-dependent mammalian cytosolic or plant chloroplast malic enzymes reveals highly conserved regions interrupted with long stretches of amino acids without significant homology.
100 citations
TL;DR: Results indicate that dehydroepiandrosterone is a typical peroxisome proliferator, which is a naturally occurring C19 steroid in mammals and the structure of which is novel compared with those of peroxISome proliferators known so far, this compound could provide particular information in the understanding of the mechanisms underlying the induction of per oxisome proliferation.
96 citations
TL;DR: In chick embryo hepatocytes in culture, factors involved in regulation of transcription by insulin, T3, and cAMP may be bound to DNA independently of hormonal treatment.
57 citations
TL;DR: The cytosolic NADP(+)-dependent malic enzyme from a cultured human breast cancer cell line was purified to near homogeneity by two highly efficient chromatography systems and is not an allosteric regulatory enzyme.
Abstract: Cytosolic NADP(+)-dependent malic enzyme from a cultured human breast cancer cell line was purified to near homogeneity by two highly efficient chromatography systems: Pharmacia-LKB Q-Sepharose anion-exchange chromatography and adenosine-2',5'-bisphosphate-agarose affinity chromatography. The overall yield was 27%. The enzyme is presumably a tetramer composed of four probably identical subunits of Mr 65,000, which is similar to the enzyme from other sources. The pI and optimum reaction pH values for the tumor malic enzyme are 5.5 and 7.2, respectively. At pH 6.9, most of the enzyme exists as monomers. Activation energy for the enzyme-catalyzed oxidative-decarboxylation reaction is 57.4 kJ/mol. The enzyme is strictly NADP+ dependent, as NAD+ cannot support the oxidative-decarboxylation reaction. ATP at low concentration inhibits the enzyme activity. Fumarate at concentrations up to 5 mM does not affect the enzymatic reaction rate. Therefore the tumor cytosolic malic enzyme, unlike the mitochondrial malic enzyme, is not an allosteric regulatory enzyme.
56 citations
TL;DR: On-going protein phosphorylation is required specifically for stimulation of transcription of the lipogenic genes by T3, suggesting that the effect of H-8 was selective.
46 citations
TL;DR: Feeding the thermogenic steroid, 5-androsten-3 beta-ol-17-one (dehydroepiandrosterone, DHEA) in the diet of rats induced the synthesis of liver mitochondrial sn-glycerol 3-phosphate dehydrogenase to levels three to five times that of control rats within 7 days.
Abstract: Feeding the thermogenic steroid, 5-androsten-3 beta-ol-17-one (dehydroepiandrosterone, DHEA) in the diet of rats induced the synthesis of liver mitochondrial sn-glycerol 3-phosphate dehydrogenase to levels three to five times that of control rats within 7 days. The previously reported enhancement of liver cytosolic malic enzyme was confirmed. The induction of both enzymes was detectable at 0.01% DHEA in the diet, reached plateau stimulation at 0.1 to 0.2%, and was completely blocked by simultaneous treatment with actinomycin D. Feeding DHEA caused smaller, but statistically significant increases of liver cytosolic lactate, sn-glycerol 3-phosphate, and isocitrate (NADP(+)-linked) dehydrogenases but not of malate or glucose 6-phosphate dehydrogenases. The capability of DHEA to enhance mitochondrial glycerophosphate dehydrogenase and malic enzyme was influenced by the thyroid status of the rats; was smallest in thyroidectomized rats and highest in rats treated with triiodothyronine. 5-Androsten-3 beta,17 beta-diol and 5-androsten-3 beta-ol-7,17-dione were as effective as DHEA in enhancing the liver mitochondrial glycerophosphate dehydrogenase and malic enzyme. Administering compounds that induce the formation of cytochrome P450 enzymes enhanced liver malic enzyme activity but not that of mitochondrial glycerophosphate dehydrogenase. Arochlor 1254 and 3-methylcholanthrene also increased the response of malic enzyme to DHEA feeding.
45 citations
TL;DR: The diurnal variations in mRNA quantities of lipogenic enzymes (acetyl-CoA carboxylase, fatty acid synthase, malic enzyme and glucose-6-phosphate dehydrogenase) in rat livers were detected but no measurable variation in any enzyme levels including fatty acid synthesis was detected.
40 citations
TL;DR: Initial velocity studies in the absence and presence of product and dead-end inhibitors suggest a steady-state random mechanism for malic enzyme in the direction of reductive carboxylation of pyruvate, consistent with an overall symmetry in the malic enzymes reaction in the two reaction directions.
36 citations
TL;DR: Significant correlation was observed between plasma insulin and hepatic lipogenic enzyme activities in untreated and vanadate-treated rats suggesting improvement in insulin sensitivity and sodium orthovanadate administration caused a shift to left in this correlation.
35 citations
34 citations
TL;DR: The results indicate that malic enzyme from human liver exhibits similar properties to the enzyme from animal liver.
Abstract: In human liver, almost 90% of malic enzyme activity is located within the extramitochondrial compartment, and only approximately 10% in the mitochondrial fraction.
Extramitochondrial malic enzyme has been isolated from the post-mitochondrial supernatant of human liver by (NH4)2SO4 fractionation, chromatography of DEAE-cellulose, ADP–Sepharose-4B and Sephacryl S-300 to apparent homogenity, as judged from polyacrylamide gel electrophoresis. The specific activity of the purified enzyme was 56 μmol · min−1· mg protein−1, which corresponds to about 10000-fold purification.
The molecular mass of the native enzyme determined by gel filtration is 251 kDa. SDS/polyacrylamide gel electrophoresis showed one polypeptide band of molecular mass 63 kDa. Thus, it appears that the native protein is tetramer composed of identical-molecular-mass subunits.
The isoelectric point of the isolated enzyme was 5.65.
The enzyme was shown to carboxylate pyruvate with at least the same rate as the forward reaction.
The optimum pH for the carboxylation reaction was at pH 7.25 and that for the NADP-linked decarboxylation reaction varied with malate concentration.
TheKm values determined at pH 7.2 for malate and NADP were 120 μM and 9.2 μM, respectively. TheKm values for pyruvate, NADPH and bicarbonate were 5.9 mM, 5.3 μM and 27.9 mM, respectively.
The enzyme converted malate to pyruvate (at optimum pH 6.4) in the presence of 10 mM NAD at approximately 40% of the maximum rate with NADP. TheKm values for malate and NAD were 0.96 mM and 4.6 mM, respectively. NAD-dependent decarboxylation reaction was not reversible.
The purified human liver malic enzyme catalyzed decarboxylation of oxaloacetete and NADPH-linked reduction of pyruvate at about 1.3% and 5.4% of the maximum rate of NADP-linked oxidative decarboxylation of malate, respectively.
The results indicate that malic enzyme from human liver exhibits similar properties to the enzyme from animal liver.
TL;DR: It is suggested that in C3 plants NADP+-linked malic enzyme is confined to the plastids and involved in biosynthesis.
Abstract: The aim of this work was to determine the maximum catalytic activity and intracellular location of NADP+-linked malic enzyme (EC 1.1.1.40) in C3 plants. Appreciable activities, ranging from 80 to 712 nmol · (gFW)−1 · min−1, were found in a wide range of tissues (roots and leaves of Pisum sativum L., cotyledons of Cucurbit a pepo Alef., developing seeds of Brassica napus L., mesocarp of Persea americana Gaertn., and suspension cultures of Glycine max L.). Overall, activity showed a rough positive correlation with biosynthesis. Differential and density-gradient fractionation of extracts of the cotyledons of germinating marrow (C. pepo) and lysates of protoplasts of suspension cultures of G. showed that the enzyme had the same distribution as the plastid marker enzymes. It is suggested that in C3 plants NADP+-linked malic enzyme is confined to the plastids and involved in biosynthesis.
TL;DR: Themalolactic enzyme of lactic acid bacteria catalyzes the decarboxylation of L-malate to L-lactate, which requires Mn2+ and NAD, which was replaceable by NH4+, for maximum activity.
Abstract: Malolactic enzyme of lactic acid bacteria catalyzes the decarboxylation of L-malate to L-lactate. The appropriate enzyme of Lactobacillus casei, Leuconostoc oenos, and Leuconostoc mesenteroides, as...
TL;DR: It is postulate that an active malic enzyme may suppress the synthesis of aspartate in hepatoma cells, but further evidence is needed to confirm this assumption.
Abstract: Parallel investigations of the transamination pathways of glutamine oxidation in Ehrlich ascites carcinoma (EAC) and AS 30D hepatoma revealed that hepatoma cells, unlike EAC, produce very little aspartate. This cannot be explained by differences in the activity of glutamine-metabolizing enzymes. Also, the mitochondria from the hepatoma respired at a similar rate to EAC mitochondria with glutamine as sole substrate producing substantial amounts of aspartate. Unlike their isolated mitochondria, intact hepatoma cells showed a very low rate of glutamine oxidation. Compared with EAC, the rate of L-[U-14C]glutamine consumption by AS 30D hepatoma cells was much lower, with insignificant production of 14C-labelled aspartate and CO2. This suggested that the glutamine-transporting system in the hepatoma cell plasma membrane had a very low activity. Isolated hepatoma mitochondria produced 3 times more pyruvate from malate than did EAC mitochondria, indicating a higher activity of NAD(P)-dependent malic enzyme. We postulate that an active malic enzyme may suppress the synthesis of aspartate in hepatoma cells, but further evidence is needed to confirm this assumption.
TL;DR: In the present work, the alkylated enzyme is shown to bind NADPH, but not L-malate in the presence of MnCl2, indicating impairment of the enzyme site for the substrate and/or divalent metal.
TL;DR: The effects of rotenone on the succinate-driven reduction of matrix nicotinamide nucleotides were investigated in Percoll-purified mitochondria from potato (Solanum tuberosum) tubers and its inhibitory effect was masked if malate had previously accumulated, owing to the malate-oxidizing enzymes.
Abstract: The effects of rotenone on the succinate-driven reduction of matrix nicotinamide nucleotides were investigated in Percoll-purified mitochondria from potato (Solanum tuberosum) tubers. Depending on the presence of ADP or ATP, rotenone caused an increase or a decrease in the level of reduction of the matrix nicotinamide nucleotides. The increase in the reduction induced by rotenone in the presence of ADP was linked to the oxidation of the malate resulting from the oxidation of succinate. Depending on the experimental conditions, malic enzyme (at pH 6.6 or in the presence of added CoA) or malate dehydrogenase (at pH 7.9) were involved in this oxidation. At pH 7.9, the oxaloacetate produced progressively inhibited the succinate dehydrogenase. In the presence of ATP the production of oxaloacetate was stopped, and succinate dehydrogenase was protected from inhibition by oxaloacetate. However, previously accumulated oxaloacetate transitorily decreased the level of the reduction of the NAD+ driven by succinate, by causing the reversal of the malate dehydrogenase reaction. Under these conditions (i.e. presence of ATP), rotenone strongly inhibited the reduction of NAD+ by succinate-driven reverse electron flow. No evidence for an active reverse electron transport through a rotenone-insensitive path could be obtained. The inhibitory effect of rotenone was masked if malate had previously accumulated, owing to the malate-oxidizing enzymes which reduced part or all of the matrix NAD+.
TL;DR: Results indicate that the arginine residue(s) may be involved in binding of the carboxyl group of the substrate to the enzyme, and protected the enzyme against inactivation, suggesting that theArginine residues are located at or near the active site of the enzyme.
TL;DR: During aging, there is a decrease in the activity of many enzymes, one of which is the superoxide dismutase enzyme involved in the protection against oxidative damage, and some chemical properties of these enzymes are studied, suggesting that the modification of histidine and lysine residues during aging could be produced by oxidation.
TL;DR: It is suggested that T3 plays a crucial role at an early step of adipose differentiation, this leading to an increased expression of a set of late adipose phenotypes such as several lipogenic enzymes.
Abstract: In the Ob 17 preadipocyte cell line, during adipose differentiation, T3 amplified the progressive expression of two enzymes of the lipogenic pathway, ATP-citrate lyase (ATP-CL) and malic enzyme (ME) as previously described for fatty acid synthase (FAS) and fatty acid synthesis, and in the same time-period of development. However, the stimulation by T3 was sustained at late stages of differentiation whereas it declined in FAS studies. The stimulation was preceded by an increase in the relative abundance of the specific mRNAs. Two ME mRNA species were detected (21S and 27S) and found to be differently distributed. Their abundance was asynchronously increased by T3 with a predominant effect on the 21S species. Culture of the cells in a thyroid-hormone depleted medium prevented any significant increase of ME activity. Early inclusion of T3 largely restored ME development whereas late elimination of T3 only moderately impaired it. It is suggested that T3 plays a crucial role at an early step of adipose differentiation, this leading to an increased expression of a set of late adipose phenotypes such as several lipogenic enzymes.
TL;DR: Under all dietary conditions studied, the increase in malic enzyme activity is associated with a decrease in the concentration of G SH, and in BSO-treated rats the decrease of GSH levels is also accompanied by an increase in the activity of malic enzymes.
TL;DR: Differences in both enzyme quantity and structure may be involved in the genetic regulation of malic enzyme activity in mice, which is considered a key lipogenic enzyme and changes in enzyme activity parallel changes in the lipogenic rate.
TL;DR: Several key enzymes related to carbohydrate metabolism were assayed in Setaria digitata and only reduced nicotinamide adenine dinucleotide (NADH) dehydrogenase, NADH oxidase and NADH-cytochrome c reductase were found in the mitochondrial fraction.
TL;DR: Results suggest that the 2′-phosphate group is crucial for the nucleotide binding to the enzyme, whereas the charge density on the C4 atom of the pyridine ring is the major factor that governs the coenzyme activity.
Abstract: Structural analogues of the NADP(+) were studied as potential coenzymes and inhibitors for NADP(+) dependent malic enzyme from Zea mays L. leaves. Results showed that 1, N(6)-etheno-nicotinamide adenine dinucleotide phosphate (∈ NADP(+)), 3-acetylpyridine-adenine dinucleotide phosphate (APADP(+)), nicotinamide-hypoxanthine dinucleotide phosphate (NHDP(+)) and β-nicotinamide adenine dinucleotide 2': 3'-cyclic monophosphate (2'3'NADPc(+)) act as alternate coenzymes for the enzyme and that there is little variation in the values of the Michaelis constants and only a threefold variation in Vmax for the five nucleotides. On the other hand, thionicotinamide-adenine dinucleotide phosphate (SNADP(+)), 3-aminopyridine-adenine dinucleotide phosphate (AADP(+)), adenosine 2'-monophosphate (2'AMP) and adenosine 2': 3'-cyclic monophosphate (2'3'AMPc) were competitive inhibitors with respect to NADP(+), while β-nicotinamide adenine dinucleotide 3'-phosphate (3'NADP(+)), NAD(+), adenosine 3'-monophosphate (3'AMP), adenosine 2': 5'-cyclic monophosphate (2'5'AMPc), 5'AMP, 5'ADP, 5'ATP and adenosine act as non-competitive inhibitors. These results, together with results of semiempirical self-consistent field-molecular orbitals calculations, suggest that the 2'-phosphate group is crucial for the nucleotide binding to the enzyme, whereas the charge density on the C4 atom of the pyridine ring is the major factor that governs the coenzyme activity.
Journal Article•
TL;DR: The derivatives at the N 6 -position have the best coenzyme activity for both enzymes, and most of the K m values were in the micromolar range which is suitable for practical use.
Abstract: This paper reports the coenzymatic properties of low molecular weight functionalized N(1)- and N 6 -(2-aminoethyl)-NAD(P), and macromolecular polyethylene glycol (M r 20,000)-N(1)-(2-aminoethyl)-NAD(P) and −N 6 -(2-aminoethyl)-NAD(P) in aqueous as well as in water-organic reaction media for the thermostable NAD(P)-dependent malic enzyme and NAD-dependent alcohol dehydrogenase from the archaebacterium Sulfolobus solfataricus. The enzymes recognize all of the derivatives tested, with V max values ranging from 30 to 250% of those for the native coenzymes. Remarkably, the malic enzyme shows higher (2.5 times) V max values for the N(1)-derivatives of NADP than for the native coenzyme. Most of the K m values were in the micromolar range which is suitable for practical use. On the basis of the k cat /K m ratios, the derivatives at the N 6 -position have the best coenzyme activity for both enzymes.
Journal Article•
TL;DR: The effects of adrenalectomy with or without replacement doses of corticosterone were examined on the levels of messenger RNA for malic enzyme and glyceraldehyde 3-phosphate dehydrogenase in adipose tissue and liver from Zucker fatty and littermate lean rats.
Abstract: The effects of adrenalectomy with or without replacement doses of corticosterone were examined on the levels of messenger RNA for malic enzyme (ME) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in adipose tissue and liver from Zucker fatty (fa/fa) and littermate lean rats. The levels of both GAPDH and ME mRNAs were increased in the obese rats. Adrenalectomy markedly reduced the m-RNA for GAPDH and ME in Zucker fatty rats to the low levels observed in adrenalectomized lean rats. Corticosterone treatment induced a greater and earlier increase in mRNA levels in adrenalectomized obese rats than in adrenalectomized lean rats. Since the fatty rat represents an autosomal recessive trait, these results are consistent with the hypothesis that the genetic defect is a loss of a modulator of steroid action which normally restricts the response of genes to glucorticoid hormones.
TL;DR: The presence of MDH in this organism is consistent with the operation of a glyoxylate cycle which, in the absence of a TCA cycle, would provide organic acids required in secondary carbon metabolism.
Abstract: A malate dehydrogenase (MDH) was characterized from the cyanobacterium Coccochloris peniocystis. The enzyme was purified approximately 180-fold and had a molecular weight of about 90000. The enzyme had a pH optimum of pH 6.7 to 7.5; a Km (malate) of 5.6 mM and Kms for NAD and NADP of 24 μM and 178 μM, respectively, although similar Vmax were obtained with either pyridine nucleotide. Enzyme activity was inhibited by ATP, citrate, oxalacetate, acetyl CoA and CoA. Enzyme assays with uniformly 14C-labelled malate caused no 14CO2 release, indicating this MDH is not a malic enzyme. Electrophoresis and S-200 gel filtration of the partially purified enzyme indicated a single MDH was present in this preparation. A second, less abundant, MDH was present in crude extracts. The presence of MDH in this organism is consistent with the operation of a glyoxylate cycle which, in the absence of a TCA cycle, would provide organic acids required in secondary carbon metabolism. ATP inhibition of MDH may allow for light regulation of MDH activity since, in the light, oxaloacetic acid is generated by phosphoenolpyruvate carboxylase activity.
01 Jan 1991-Zentralblatt Fur Bakteriologie-international Journal of Medical Microbiology Virology Parasitology and Infectious Diseases
TL;DR: Findings reveal the significant heterogeneity in G.C. lamblia isolates both from widely separated areas and within a single region and may explain the variable clinical manifestations, host response and treatment efficacy characteristic of human giardiasis.
Abstract: Electrophoretic mobility patterns of six enzymes, viz. alkaline phosphatase E.C. 3.1.3.1., acid phosphatase E.C. 3.1.3.2., malic enzyme E.C. 1.1.1.40., phosphoglucomutase E.C. 2.7.5.1., isocitrate dehydrogenase E.C. 1.1.1.42., glucose-6-phosphate dehydrogenase E.C. 1.1.1.49 of two axenically cultured human Giardia lamblia isolated from India (PD-1 and PD-2) and one strain from Portland, Oregon, USA (P-1) were compared using polyacrylamide gel electrophoresis (PAGE). Based on the difference in the mobility patterns of the enzymes phosphoglucomutase, isocitrate dehydrogenase and malic enzyme, the PD-1 and PD-2 isolates appeared to be quite different from P-1. In the present study, the isocitrate dehydrogenase and alkaline phosphatase enzymes were used for the first time for differentiation of Giardia isolates. In the case of PD-1, two alkaline phosphatase bands could be seen whereas only one band was observed in PD-2 and P-1. Thus, the three strains could be grouped into three different zymodemes. These findings reveal the significant heterogeneity in G. lamblia isolates both from widely separated areas and within a single region. Heterogeneity among G. lamblia strains may explain the variable clinical manifestations, host response and treatment efficacy characteristic of human giardiasis.
TL;DR: Although estrogen is known to induce both enzymes, the temporal changes in enzyme activity in pregnancy cannot be related to the action of estrogen alone and although no direct action of progesterone on these enzymes has yet been proposed, further work on its effects on enzyme activity and distribution is indicated.
Abstract: Using techniques of microdissection and microassay as well as qualitative histochemistry the activity and intra-acinar distribution of G6PDH and ME were studied on selected days of pregnancy in the rat. Both enzymes show distinct fluctuations during the course of pregnancy in keeping with changes in hepatic lipogenesis. Marked increases in activity are seen as early as the 4th day, while highest values are attained on day 20, with a predominant perivenous induction. On day 22, just before parturition a sharp decrease of both enzyme activities with a flattening of the periportal/perivenous gradient was detected. G6PDH shows proportionally considerably larger increases and more distinct changes in zonation. The perivenous fluctuations in G6PDH activity of late gestation are supposed to be caused primarily by insulin. Although estrogen is known to induce both enzymes, the temporal changes in enzyme activity in pregnancy cannot be related to the action of estrogen alone. The changes in enzyme activity, however, correspond well to those of progesterone, and although no direct action of progesterone on these enzymes has yet been proposed, further work on its effects on enzyme activity and distribution is indicated.
TL;DR: Northern-blot analysis demonstrated that the two major malic enzyme mRNA species displayed non-co-ordinate control during development, with the 2.0 kb form accumulating to a greater extent than the 3.1 kb form.
Abstract: The expression of hepatic cytosolic malic enzyme in the developing rat has been studied by molecular-biological techniques. Malic enzyme mRNA was barely detectable throughout the neonatal period, but increased to significant levels immediately before weaning. Northern-blot analysis demonstrated that the two major malic enzyme mRNA species displayed non-co-ordinate control during development, with the 2.0 kb form accumulating to a greater extent than the 3.1 kb form. A novel 1.6 kb mRNA species was found to predominate in foetal samples. Tri-iodothyronine treatment of neonatal rats caused premature induction of all three malic enzyme mRNA species. Dietary studies also showed precocious induction of the mRNA with diets high in carbohydrate, but not with those high in fat.
TL;DR: The data suggest that insulin may act on malic enzyme synthesis through its general stimulatory effect on protein synthesis, or by antagonizing factors that inhibit the induction of this enzyme.
Abstract: We examined the effects of T3 and insulin on the activity of hepatic mitochondrial alpha-glycerophosphate dehydrogenase and cytosolic malic enzyme in control, thyroidectomized, thyroidectomized food-restricted, and thyroidectomized diabetic rats. In the three untreated thyroidectomized groups, the decrease in hepatic nuclear T3 content was accompanied by a marked reduction in the levels of alpha-glycerophosphate dehydrogenase and malic enzyme activity. Although the levels of both enzymes were increased by a receptor-saturating dose of T3, the alpha-glycerophosphate dehydrogenase response in the thyroidectomized groups was almost identical to that in controls, whereas that of malic enzyme was reduced to 45-62% of control values. Insulin failed to stimulate the alpha-glycerophosphate dehydrogenase levels in untreated and T3-treated thyroidectomized groups, but caused an increase in malic enzyme activity by 79-130% in untreated thyroidectomized groups, and enhanced the activity of this enzyme to about twice that seen with T3 alone. These effects were independent of changes in nuclear T3 binding parameters. The data suggest that insulin may act on malic enzyme synthesis through its general stimulatory effect on protein synthesis, or by antagonizing factors that inhibit the induction of this enzyme.