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PubMed1982

Effects of garlic on lipid metabolism in rats fed cholesterol or lard.

Effects of garlic on lipid metabolism were studied in three experiments using different aged male rats fed a diet containing 1% cholesterol or 15% lard. Lyophilized garlic was supplemented at 2% and 4% of the diet. Plasma glucose was not changed by dietary treatments. Rats fed cholesterol and lard diets increased plasma cholesterol and triglycerides compared to controls. Garlic decreased plasma cholesterol in cholesterol- and lard-fed rats, but decreased plasma triglycerides only in the lard-fed group. Garlic supplementation decreased very low density lipoprotein cholesterol and increased high density lipoprotein cholesterol. The liver weight, total liver lipid and cholesterol were increased in rats fed the cholesterol diet but a supplementation of garlic decreased those parameters by about 30%. Dietary cholesterol and lard decreased hepatic glucose-6-phosphate dehydrogenase and malic enzyme activities: the garlic supplementation further decreased these enzyme activities. Garlic feeding increased the excretion of the neutral steroids in both 16-week and 10-week-old rats and bile acids in only 16-week-old pair-fed rats. Garlic at the 2% level was similarly effective on lipid metabolism as at 4%. These results demonstrate that garlic increases the excretion of neutral and acidic steroids and exerts hypocholesterolemic effects in cholesterol-fed rats.

Adipose Tissue↗
PubMed1999

Phosphoenolpyruvate carboxykinase is involved in the decarboxylation of aspartate in the bundle sheath of maize

We recently showed that maize (Zea mays L.) leaves contain appreciable amounts of phosphoenolpyruvate carboxykinase (PEPCK; R.P. Walker, R.M. Acheson, L.I. Tecsi, R.C. Leegood [1997] Aust J Plant Physiol 24: 459-468). In the present study, we investigated the role of PEPCK in C4 photosynthesis in maize. PEPCK activity and protein were enriched in extracts from bundle-sheath (BS) strands compared with whole-leaf extracts. Decarboxylation of [4-14C]aspartate (Asp) by BS strands was dependent on the presence of 2-oxoglutarate and Mn2+, was stimulated by ATP, was inhibited by the PEPCK-specific inhibitor 3-mercaptopicolinic acid, and was independent of illumination. The principal product of Asp metabolism was phosphoenolpyruvate, whereas pyruvate was a minor product. Decarboxylation of [4-14C]malate was stimulated severalfold by Asp and 3-phosphoglycerate, was only slightly reduced in the absence of Mn2+ or in the presence of 3-mercaptopicolinic acid, and was light dependent. Our data show that decarboxylation of Asp and malate in BS cells of maize occurs via two different pathways: Whereas malate is mainly decarboxylated by NADP-malic enzyme, decarboxylation of Asp is dependent on the activity of PEPCK.

Journal Article↗
PubMedDate not supplied

[Formate metabolism by lactate-producing and lactate-utilizing rumen bacteria].

Physiological concentrations [< 11 mM] of formate do not violate the metabolism of S. bovis and M. elsdenii. A significant inhibition is caused by concentrations of 22 and 44 mM. In this case the process of ammonia formation in S. bovis is inhibited more pronouncedly. Peculiar effects of formate (11 mM) on LDH, FDH, aconitase, isocitrate dehydrogenase, fumarase, L-MDH and malic-enzyme have been stated. The changes show that it enhances assimilation of sugars fermented to lactate in S. bovis, in contrast to M. elsdenii, where it activates the utilization of lactic acid. During the log-phase S. bovis utilized only 11.5% of [14C] H2O2, whereas M. elsdenii uses 33.4% of it. The major amount of the label is transferred from intracellular inclusions to nucleic acids (in S. bovis--74.7%, in M. elsdenii--87%) and then incorporated into low molecular substances (23.5 and 11.9%, respectively), the rest being incorporated into proteins and lipids.

Animals↗
PubMed1976

Replenishment and depletion of citric acid cycle intermediates in skeletal muscle. Indication of pyruvate carboxylation.

The effects of various substrates on the concentrations of free amino acids, citric acid cycle intermediates and acylcarnitines were studies in perfused hindquarter of rat in presence of glucose and insulin in order to assess regulatory mechanisms of the level of citric acid cycle intermediates in skeletal muscle. 1. Acetate and acetoacetate effected a significant increase in the level of citrate cycle intermediates and accumulation of acetylcarnitine. These changes were accompanied by a reduction in the level of alanine. The concentration of AMP was significantly elevated. 2. Muscle mitochondria fixed 14CO2 in the presence of pyruvate. The products were identified as malate or citrate when whole and disintegrated mitochondria were used respectively. The fixation was greatly stimulated by acetylcarnitine. 3. Acetylcarnitine inhibited the production of pyruvate from malate by muscle mitochondria. 4. Perfusion with 2-oxoisocaproate and 2-oxoisovalerate promoted increases in the level of citric cycle intermediates, a drop in both alanine and glutamate, and accumulation of branched-chain acylcarnitines. 2-Oxoisocaproate also caused a reduction of alanine released from the muscle. 5. Perfusion with leucine and valine did not change the concentration of citric acid cycle intermediates, but elevated glutamate and still more the concentration of alanine. 6. It is concluded that citric cycle intermediate level in the perfused resting muscle is modified by a) conditions which change the concentration of acetyl-CoA and thereby modify the rate of pyruvate carboxylation and decarboxylation of malate via malic enzyme b) conditions which change the concentration of pyruvate cause changes in alanine and cycle intermediates in the same direction via transamination reactions c) conditions which change the concentrations of 2-oxoacids which are converted to cycle intermediates via oxidation.

Acetyl Coenzyme A↗
PubMed1998

Nuclear sterol regulatory element-binding proteins activate genes responsible for the entire program of unsaturated fatty acid biosynthesis in transgenic mouse liver.

Previous studies have shown that the rate of fatty acid synthesis is elevated by more than 20-fold in livers of transgenic mice that express truncated nuclear forms of sterol regulatory element-binding proteins (SREBPs). This was explained in part by an increase in the levels of mRNA for the two major enzymes of fatty acid synthesis, acetyl-CoA carboxylase and fatty acid synthase, whose transcription is stimulated by SREBPs. Fatty acid synthesis also requires a source of acetyl-CoA and NADPH. In the current studies we show that the levels of mRNA for ATP citrate lyase, the enzyme that produces acetyl-CoA, are also elevated in the transgenic livers. In addition, we found marked elevations in the mRNAs for malic enzyme, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase, all of which produce NADPH. Finally, we found that overexpressing two of the SREBPs (1a and 2) led to elevated mRNAs for stearoyl-CoA desaturase 1 (SCD1), an isoform that is detectable in nontransgenic livers, and SCD2, an isoform that is not detected in nontransgenic livers. This stimulation led to an increase in total SCD activity in liver microsomes. Together, all of these changes would be expected to lead to a marked increase in the concentration of monounsaturated fatty acids in the transgenic livers, and this was confirmed chromatographically. We conclude that expression of nuclear SREBPs is capable of activating the entire coordinated program of unsaturated fatty acid biosynthesis in mouse liver.

ATP Citrate (pro-S)-Lyase↗
PubMed1998

Identification and mapping of two divergent, unlinked major histocompatibility complex class II B genes in Xiphophorus fishes.

We have isolated two major histocompatibility complex (MHC) class II B genes from the inbred fish strain Xiphophorus maculatus Jp 163 A. We mapped one of these genes, designated here as DXB, to linkage group III, linked to a malic enzyme locus, also syntenic with human and mouse MHC. Comparison of genomic and cDNA clones shows the gene consists of six exons and five introns. The encoded beta1 domain has three amino acids deleted and a cytoplasmic tail nine amino acids longer than in other teleost class II beta chains, more similar to HLA-DRB, clawed frog Xela-F3, and nurse shark Gici-B. Key residues for disulfide bonds, glycosylation, and interaction with alpha chains are conserved. These same features are also present in a swordtail (Xiphophorus helleri) genomic DXB PCR clone. A second type of class II B clone was amplified by PCR from X. maculatus and found to be orthologous to class II genes identified in other fishes. This DAB-like gene is 63% identical to the X. maculatus DXB sequence in the conserved beta2-encoding exon and was mapped to new unassigned linkage group LG U24. The DXB gene, then, represents an unlinked duplicated locus not previously identified in teleosts.

Amino Acid Sequence↗
PubMed1984

Regulation of aflatoxin biosynthesis: effect of glucose on activities of various glycolytic enzymes.

Catabolism of carbohydrates has been implicated in the regulation of aflatoxin synthesis. To characterize this effect further, the activities of various enzymes associated with glucose catabolism were determined in Aspergillus parasiticus organisms that were initially cultured in peptone-mineral salts medium and then transferred to glucose-mineral salts and peptone-mineral salts media. After an initial increase in activity, the levels of glucose 6-phosphate dehydrogenase, mannitol dehydrogenase, and malate dehydrogenase were lowered in the presence of glucose. Phosphofructokinase activity was greater in the peptone-grown mycelium, but fructose diphosphatase was largely unaffected by carbon source. Likewise, carbon source had relatively little effect on the activities of pyruvate kinase, malic enzyme, isocitrate-NADP dehydrogenase, and isocitrate-NAD dehydrogenase. The results suggest that glucose may, in part, regulate aflatoxin synthesis via a carbon catabolite repression of NADPH-generating and tricarboxylic acid cycle enzymes.

Aflatoxins↗
PubMed1997

Supply-Side Analysis of Growth of Bacillus subtilis on Glucose-Citrate Medium: Feasible Network Alternatives and Yield Optimality.

Our prior work revealed that compared to the case for glucose metabolism, increased carbon yield and nil acid formation result when Bacillus subtilis grows on glucose medium containing citrate. To scrutinize further how citrate addition may alter metabolic flux regulation and the degree that the observed carbon yield corresponds to the maximal value, experimental (by least-squares analysis) and optimal (by linear programming) fluxes and yields were contrasted. Networks with differing reaction routes, directionality constraints, and transhydrogenase activities were examined. To attain an elevated carbon yield, citrate-glucose utilization need not alleviate any stoichiometric constraints that can sometimes interfere with the attainment of network objectives. Rather, the high carbon yield and nil acid formation attained may be linked to restriction of glycolytic capacity, particularly at the level of pyruvate kinase, which is consistent with a hypothesized effect of coupled metal-citrate uptake. Allowing for malic enzyme activity, hexose monophosphate pathway cycling, and transhydrogenase activity may also lead to the flux distributions underlying the high carbon yield observed. Finally, the observed carbon yield corresponded well to the maximum yield provided by all the network alternatives examined. Collectively, these results suggest that (i) the observed carbon yield is essentially equal to the maximal values associated with plausible networks and (ii), as suggested by others, nonoptimal flux regulation may contribute significantly to apparent cellular maintenance requirements.

Journal Article↗
PubMed1994

Characterization of thyroid hormone (T3) receptors in three osteosarcoma cell lines of distinct osteoblast phenotype: interactions among T3, vitamin D3, and retinoid signaling.

T3 is required for normal skeletal development, but its cellular targets in bone are unknown. T3 regulates target gene transcription via a specific nuclear receptor (T3R), which can heterodimerize with 9-cis-retinoic acid, 1 alpha, 25-dihydroxyvitamin D3, or retinoic acid receptors to modify T3 responsiveness. Serum-free cultures were developed to investigate hormone interactions in three osteosarcoma cell lines, ROS25/1, UMR106, and ROS17/2.8, that express fibroblast-like, preosteoblast, and mature osteoblast phenotypes. ROS25/1 expressed T3R alpha 1, but only low levels of T3R beta 1, whereas UMR106 and ROS17/2.8 cells expressed both receptor proteins. All cells expressed c-erb-A alpha 2 protein and equal levels of 1 alpha,25-dihydroxyvitamin D3 receptor, 9-cis-retinoic acid receptor, and retinoic acid receptor messenger RNAs. Endogenous T3R activity and the effects of D3 and 9-cis-RA on T3 responsiveness were determined in transfections using reporter genes containing T3 response elements from rat malic enzyme or alpha-myosin heavy chain genes. Cell-specific T3 responses were associated with differing patterns of T3R gene expression and stages of osteoblast phenotype expression. A change in T3R beta 1 gene expression during osteoblast phenotype differentiation may modify T3 action in developing bone.

Animals↗
PubMedDate not supplied

Physiological differentiation of the mitochondria during Bufo bufo development.

1) The oxygen consumption increases during Bufo bufo development in accordance with the two steps which border at the "heart beat" stage. 2) Cytochrome c oxidase activity is not proportional to the oxygen consumption: it is notable and constant in the first step, and it only increases in the second. 3) In the mitochondria of preneural embryos, citrate synthase, NADP+ dependent isocitrate dehydrogenase, and succinate dehydrogenase activities are very low in respect to malate dehydrogenase and glutamate oxaloacetate transaminase activities. The Krebs cycle results lowered at the condensing reaction level with acetyl accumulation when pyruvate is available. The same behavior has been observed in the Xenopus laevis oocytes and differentiated tissues. 4) The presence of a phosphagen system which is different from creatine phosphate and arginine phosphate, supporting ATP level, has been demonstrated in B. bufo embryos. 5) Mitochondria of postneural embryos are able to accomplish a complete Krebs cycle by increasing citrate synthase, and succinate dehydrogenase activities. 6) In all B. bufo development, malate dehydrogenase and glutamate oxaloacetate transaminase constitute a multienzymatic system by which the mitochondria accomplish a decarboxylic amino acid shunt required for the transformation of deutoplasm into protoplasm. This shunt is also operative in the X. laevis oocytes. 7) Through pyruvate production, by oxidative decarboxylation of malate, the NAD(P)+ dependent malic enzyme could carry out a fundamental anaplerotic function in the mitochondria which is specialized in the production of biosynthetic blocks belonging to the embryo in which the carbohydrates metabolism rather than the glycolytic activity is designed for pentose phosphate and glycerol phosphate synthesis for protein and cytomembrane production. 8) Consistent metabolic differences have been highlighted between B. bufo embryos and X. laevis embryos.

Animals↗
PubMed1978

[Changes in mammary tissue lipid metabolism in the goats during the first 2 months of lactation].

5 French Alpine Goats were studied after normal or premature parturition. Mammary tissue acetyl-C oA carboxylase, glucose-6-phosphate dehydrogenase, malic enzyme and lipoprotein lipase (LPL) activities varied in parallel with milk fat secretion from the 3rd to the 9th week of lactation. Variations of mammary LPL activity and of long chain fatty acid secretion were positively highly correlated during that period. In goats with normal parturition, lipogenic activities seemed to reach a maximum level shortly after parturition. There was a positive correlation between mammary Ll activities and plasma non esterified fatty acid contents, possibly reflecting a relationship between adipose tissue mobilisation and mammary metabolism.

Acetyl-CoA Carboxylase↗
PubMed1986

Malnutrition at the cellular level in uremia: a new frontier for research.

Previously reported studies showed that protein-calorie malnutrition (PCM) in children is associated with significant alterations in muscle cell composition, characterized by increased cell water and Na, with decreased concentrations of K, Mg, and some glycolytic and citric acid cycle metabolites. In PCM, the i.c. H2O and levels of Na and K were significantly related, by multiple regression analysis, to the combined set of simultaneously measured levels of cell metabolites, phosphoenolpyruvate, pyruvate, alpha-ketoglutarate, and oxaloacetate. Cell bioactivities also were affected by PCM. Activities of the enzymes pyruvate kinase and malic and isocitric dehydrogenases were significantly reduced in muscle homogenates of PCM children. Kinetic analysis of pyruvate kinase indicated an 8-10-fold reduction in maximal velocity of the enzyme, consistent with a reduction in enzyme protein. Additionally, reduced levels of ATP and the equilibrium constant of the adenylate kinase system were observed in leukocytes of PCM children. Alterations in the activity of the energy-dependent Na pump have been noted by others in association with the accumulation of i.c. Na in severe malnutrition. Neither protein synthesis nor amino acid pools was measured in these previously reported studies. Recent data from several laboratories show that the "profiles" of i.c. and plasma amino acids are very different, both in uremics and in control subjects. In control subjects, with leukocytes as the cell model, the level of protein synthesis can be predicted by multiple regression analyses from simultaneously measured levels of plasma or i.c. amino acids. Intracellular amino acids are better predictors. Of 19 intracellular amino acids, a combination of five accounted for 54% of the variance in protein synthesis in normal, healthy adults. Levels of these predictor cell amino acids can, in turn, be predicted by different combinations of apparently unrelated plasma amino acids. In adult uremic patients stabilized by hemodialysis, with leukocytes as the cell model, levels of ATP, energy charge, adenylate kinase and pyruvic kinase activities were reduced. Others have reported increased i.c. water and Na contents, and impaired Na pump activity. Cell levels of methionine and the branched-chain amino acids, valine, leucine, and isoleucine, and protein synthesis also were significantly reduced. By multiple regression analysis, the observed levels of protein synthesis and energy charge in the hemodialyzed uremic patients were largely accounted for by different combinations of intracellular amino acid than in healthy subjects.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1983

Nuclear thyroid hormone receptors, alpha-glycerophosphate dehydrogenases, and malic enzyme in N-nitrosomethylurea-induced rat mammary tumors.

Specific L-3,3'5-triiodothyronine (triiodothyronine) binding by isolated nuclei was determined in N-nitrosomethylurea-induced mammary carcinomas and livers from intact and thyroidectomized animals. Tumors contained a single class of high-affinity nuclear triiodothyronine binding sites with characteristics similar to those of hepatic nuclei. Competition experiments showed the relative affinities of thyroid hormone structural analogues for both tumor and liver receptors to be: triiodothyroacetic acid greater than triiodothyronine greater than thyroxine greater than reverse triiodothyronine. Diiodotyrosine did not complete for the binding sites. Mammary tumors exhibited a wide range of binding sites, but most were in the range of 50 to 150 fmol/micrograms DNA. The levels were not affected significantly by hypothyroidism. Liver triiodothyronine receptor concentrations were approximately 5-fold those of tumors; they were unaffected by low serum thyroid hormone levels and were similar to those of non-tumor-bearing, euthyroid controls. Mitochondrial alpha-glycerophosphate dehydrogenase and cytosolic malic enzyme activities were reduced in both tumors and livers of hypothyroid rats; cytosolic alpha-glycerophosphate dehydrogenase levels were unchanged. Hepatic enzyme activities were similar in euthyroid tumor-bearing animals and in euthyroid healthy controls.

Animals↗
PubMed1988

Presence of anaplerotic reactions and transamination, and the absence of the tricarboxylic acid cycle in mollicutes.

Cell extracts of the fermentative Mollicutes Acholeplasma laidlawii B-PG9, Acholeplasma morum S2, Mycoplasma capricolum 14, Mycoplasma gallisepticum S6, Mycoplasma pneumoniae FH, Mycoplasma hyopneumoniae J and M. genitalium G-37, and the non-fermentative Mycoplasma hominis PG-21, Mycoplasma hominis 1620 and Mycoplasma bovigenitalium PG-11 were examined for 39 cytoplasmic enzyme activities associated with the tricarboxylic acid (TCA) cycle, transamination, anaplerotic reactions and other enzyme activities at the pyruvate locus. Malate dehydrogenase (EC 4.2.1.2) was the only TCA-cycle-associated enzyme activity detected and it was found only in the eight Mycoplasma species. Aspartate aminotransferase (EC 2.6.1.1) activity was detected in all Mollicutes tested except M. gallisepticum S6. Malate synthetase (EC 4.1.3.2) activity, in the direction of malate formation, was found in the eight Mycoplasma species, but not in any of the Acholeplasma species. Phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) was detected in the direction of oxaloacetate (OAA) formation in both Acholeplasma species, but not in any of the Mycoplasma species. Pyruvate carboxylase (EC 6.4.1.1), pyruvate kinase (EC 2.7.1.40), pyruvate dehydrogenase (EC 1.2.4.1) and lactate dehydrogenase (EC 1.1.1.27) activities were found in all ten Mollicutes tested. No activities were detected in any of the ten Mollicutes for aspartase (EC 4.3.1.1), malic enzyme (EC 1.1.1.40), PEP carboxytransphosphorylase (EC 4.1.1.38), PEP carboxykinase (EC 4.1.1.32) or pyruvate orthophosphate dikinase (EC 2.7.9.1). In these TCA-cycle-deficient Mollicutes the pyruvate-OAA locus may be a point of linkage for the carbons of glycolysis, lipid synthesis, nucleic acid synthesis and certain amino acids. CO2 fixation appears obligatory in the Acholeplasma species and either CO2 fixation or malate synthesis appears obligatory in the Mycoplasma species.

Acholeplasma↗
PubMed1994

Lipogenic activities in rat liver are subjected to circadian rhythms.

Diurnal variations were investigated in the activities of the key lipogenic enzymes in rat liver under standard experimental conditions. Fatty acid synthetase, acetyl-CoA-carboxylase, and ATP-citrate lyase showed sinusoidal circadian rhythms (statistically sustained), reaching maximum activity at night and minimum during the light period, with a fold increase value of 1.7, 2.2 and 3.2, respectively. Although a non-sinusoidal circadian rhythm was observed in the malic enzyme activity, statistically different time-dependent activity values were detected throughout a day. The observed rhythms run in parallel with that previously reported for glucose-6-phosphate dehydrogenase, suggesting a whole circadian regulation for rat liver lipogenesis.

ATP Citrate (pro-S)-Lyase↗