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PubMed1983

Mechanisms responsible for the inhibitory effects of benfluorex on hepatic intermediary metabolism.

The effects of benfluorex on hepatic intermediary metabolism have been studied using the isolated hepatocyte system. The drug inhibits the synthesis of both glucose and fatty acids by hepatocytes. Evidence is obtained that hepatocytes rapidly split benfluorex into benzoic acid and 1-(3-trifluoromethylphenyl)-2-[N-(2-hydroxyethyl)amino]propane (THEP). Comparison of the effects of the parent compound with the effects of THEP and benzoic acid on gluconeogenesis and on fatty acid synthesis indicates that different metabolites of the drug are responsible for its various actions: THEP inhibits gluconeogenesis, whereas benzoic acid inhibits fatty acid synthesis. The latter pathway appears to be inhibited at two sites: mitochondrial pyruvate uptake is inhibited by benfluorex itself, whereas fatty acid synthase is inhibited by benfluorex-derived benzoic acid.

Animals↗
PubMed1982

[Mechanisms of the regulation of muscle energy metabolism on oxidation of glucose and fatty acids. A mathematical model].

A mathematical model was used to study the role of various allosteric regulatory mechanisms in the oxidation of glucose and fatty acids by muscle energy metabolism. A large number of such mechanisms were shown to be involved in simultaneous oxidation of both substrates: glycolysis is regulated by the ATP/ADP ratio at the phosphofructokinase (PFK) step; the control over pyruvate dehydrogenase is exercised by the NADHm/NADm+ and CoAsAc/CoAsH ratios as well as by the level of pyruvate; the Krebs cycle is regulated by oxaloacetate and citrate concentrations in the citrate synthase reaction and by the ATP/ADP and NADHm/NADm+ ratios in the isocitrate dehydrogenase reaction. The inhibition of PFK and pyruvate dehydrogenase by excess of CoAsAcyl as well as the inhibition of PFK by citrate are additional equivalent regulatory mechanisms. When glucose alone is oxidized, the levels of citrate, CoAsAcyl, NADHm and CoAsAc decrease drastically within the whole range of physiological ATPase loads; the only regulating factors that remain efficient are the ATP/ADP ratio in glycolysis, the level of pyruvate at the pyruvate dehydrogenase step, the ATP/ADP ratio and the levels of CoAsAc, oxaloacetate and isocitrate in the Krebs cycle.

Adenosine Diphosphate↗
PubMed1979

Chronic hyperinsulinemia in the fetal rhesus monkey: effects on hepatic enzymes active in lipogenesis and carbohydrate metabolism.

Hyperinsulinemia was produced in fetal rhesus monkeys for 21 days in the last third of gestation by subcutaneous pork insulin injected at 19 U a day. Plasma insulin concentrations in treated fetuses (N = 4) were 3525 microU/ml. There was no difference in paired pre- and post-treatment fetal plasma glucose concentration. Activity of the hepatic enzymes that promote glucose utilization (glucokinase and hexokinase) and glycolysis (phosphofructokinase, pyruvate kinase, and pyruvate dehydrogenase) was unaffected. Similarly, glycogen metabolism enzymes (active and inactive synthase and phosphorylase) were unaltered. Two gluconeogenic enzymes (PEPCK and glucose-6-phosphatase) were diminished in the treated group compared with controls. Fetal hyperinsulinemia enhanced lipogenic and NADPH-producing enzyme activities, as evidenced by a twofold increase in fatty acid synthase and in citrate cleavage enzyme activity. Malic enzyme was absent. Hyperinsulinemia with euglycemia (1) increases the activity of enzymes that participate in lipogenesis, (2) decreases some of those controlling gluconeogenesis, and (3) has no effect on the enzymes of glycolysis.

Animals↗
PubMed1995

Metabolic engineering of Lactococcus lactis: influence of the overproduction of alpha-acetolactate synthase in strains deficient in lactate dehydrogenase as a function of culture conditions.

The als gene for alpha-acetolactate synthase of Lactococcus lactis MG1363 was cloned on a multicopy plasmid under the control of the inducible L. lactis lacA promoter. More than a hundredfold overproduction of alpha-acetolactate synthase was obtained in L. lactis under inducing conditions as compared with that of the host strain, which contained a single chromosomal copy of the als gene. The effect of alpha-acetolactate synthase overproduction on the formation of end products in various L. lactis strains was studied under different fermentation conditions. Under aerobic conditions and with an initial pH of 6.0, overexpression of the als gene resulted in significant acetoin production that amounted to more than one-third of the pyruvate converted. However, the effect of the alpha-acetolactate synthase overproduction was even more pronounced in the lactate dehydrogenase-deficient strain L. lactis NZ2700. Anaerobic cultivation of this strain resulted in a doubling of the butanediol formation of up to 40% of the converted pyruvate. When cultivated aerobically at an initial pH of 6.8, overexpression of the als gene in L. lactis NZ2700 resulted in the conversion of more than 60% of the pyruvate into acetoin, while no butanediol was formed. Moreover, at an initial pH of 6.0, similar amounts of acetoin were obtained, but in addition approximately 20% of the pyruvate was converted into butanediol. These metabolic engineering studies indicate that more than 80% of the lactose can be converted via the activity of the overproduced alpha-acetolactate synthase in L. lactis.

Acetolactate Synthase↗
PubMed1996

Metabolic activities of metronidazole-sensitive and -resistant strains of Helicobacter pylori: repression of pyruvate oxidoreductase and expression of isocitrate lyase activity correlate with resistance.

In this study, we compared metronidazole (Mtz)-sensitive and -resistant strains of Helicobacter pylori for metabolic differences that might correlate with drug resistance. Included in this study was an isogenic Mtz(r) strain, HP1107, that was constructed by transforming genomic DNA from Mtz(r) strain HP439 into Mtz(s) strain HP500. Enzyme activities were also measured for Mtz(r) strains grown in the presence or absence of 18 micrograms of metronidazole per ml (ca. one-half of the MIC). These studies confirmed the presence of the Embden-Meyerhof-Parnas, Entner-Doudoroff, and pentose pathways. H. pylori strains expressed enzymatic activities indicative of a complete and active Krebs cycle. All strains expressed pyruvate oxidoreductase (POR) and alpha-ketoglutarate oxidoreductase (KOR) as measured with the redox-active dye benzyl viologen (30 to 96 nmol/min/mg of protein for POR and 30 nmol/min/mg of protein for KOR). When grown in the presence of Mtz at > or = 3.5 micrograms/ml, Mtz(r) strains expressed no detectable POR or KOR activity. The apparent repression of POR and KOR activities by Mtz affected bacterial growth as manifest by extended lag periods and growth yield reductions of > 30%. A dose-dependent relationship was demonstrated between the metronidazole concentration in the growth medium and the specific activity of POR measured in bacterial cell extracts. The observed repression was not due to inactivation of POR by Mtz. In addition to repression of POR and KOR activities, growth in the presence of Mtz also led to decreases in the activities of various Krebs cycle enzymes, including aconitase, isocitrate dehydrogenase and succinate dehydrogenase. All of the Mtz(r) strains examined expressed isocitrate lyase and malate synthase activities indicative of the glyoxylate bypass. No isocitrate lyase activity was detected in Mtz(s) strain HP500. Isocitrate lyase activity was expressed by HP500 following transformation to Mtz resistance (Mtz(r) strain HP1107) with DNA from an Mtz(r) strain. The results of this study suggest that Mtz resistance may be a recessive trait, possibly involving inactivation of a regulatory gene, that results in constitutive expression of isocitrate lyase. Repression of POR and KOR activities in response to low levels of Mtz may be a general response of H. pylori strains to Mtz, but only resistant strains manage to survive via activation of compensatory metabolic pathways.

Citric Acid Cycle↗
PubMed2004

Proteomic analysis of proteins associated with lipid droplets of basal and lipolytically stimulated 3T3-L1 adipocytes.

Adipocytes hold the body's major energy reserve as triacylglycerols packaged in large lipid droplets. Perilipins, the most abundant proteins on these lipid droplets, play a critical role in facilitating both triacylglycerol storage and hydrolysis. The stimulation of lipolysis by beta-adrenergic agonists triggers rapid phosphorylation of perilipin and translocation of hormone-sensitive lipase to the surfaces of lipid droplets and more gradual fragmentation and dispersion of micro-lipid droplets. Because few lipid droplet-associated proteins have been identified in adipocytes, we isolated lipid droplets from basal and lipolytically stimulated 3T3-L1 adipocytes and identified the component proteins by mass spectrometry. Structural proteins identified in both preparations include perilipin, S3-12, vimentin, and TIP47; in contrast, adipophilin, caveolin-1, and tubulin selectively localized to droplets in lipolytically stimulated cells. Lipid metabolic enzymes identified in both preparations include hormone-sensitive lipase, lanosterol synthase, NAD(P)-dependent steroid dehydrogenase-like protein, acyl-CoA synthetase, long chain family member (ACSL) 1, and CGI-58. 17-beta-Hydroxysteroid dehydrogenase, type 7, was identified only in basal preparations, whereas ACSL3 and 4 and two short-chain reductase/dehydrogenases were identified on droplets from lipolytically stimulated cells. Additionally, both preparations contained FSP27, ribophorin I, EHD2, diaphorase I, and ancient ubiquitous protein. Basal preparations contained CGI-49, whereas lipid droplets from lipolytically stimulated cells contained several Rab GTPases and tumor protein D54. A close association of mitochondria with lipid droplets was suggested by the identification of pyruvate carboxylase, prohibitin, and a subunit of ATP synthase in the preparations. Thus, adipocyte lipid droplets contain specific structural proteins as well as lipid metabolic enzymes; the structural reorganization of lipid droplets in response to the hormonal stimulation of lipolysis is accompanied by increases in the relative mass of several proteins and the recruitment of additional proteins.

3T3-L1 Cells↗
PubMedDate not supplied

Regional differences of substrate oxidation capacity in rat hearts: effects of extra load and endurance training.

Male rats, aged 17 weeks at the end of experiments, were divided into four groups. Two groups lived in normal cage conditions with or without extra load (20% of the body weight) and two groups were trained by running with or without extra load for 8 weeks. Oxidation rates of succinate, glutamate + malate, palmitoylcarnitine, and pyruvate, and the activities of lactate dehydrogenase, citrate synthase, isocitrate dehydrogenase and cytochrome oxidase were measured in homogenates of the right ventricle and in those of the subendocardial and subepicardial layers of the left ventricle. Oxidation rates of succinate and palmitoylcarnitine tended to be higher in the subendocardium than in the subepicardium of sedentary control animals (p less than 0.1 and p less than 0.05, respectively). Transmural differences of succinate and palmitoylcarnitine oxidation rates were even more clear after running training (p less than 0.01 and p less than 0.05, respectively), after carrying extra load (p less than 0.001 and p less than 0.001, respectively) and after training carrying extra load (p less than 0.001 and p less than 0.05, respectively). Training also enhanced pyruvate oxidation rate in the subendocardium. Oxidation rates of all substrates were lower in the right ventricle than in the left ventricle. In control animals there were no regional differences in the myocardial enzyme activities and the training- or extra-load-induced changes were modest compared with the changes in the oxidation rates. The most significant change was the training-induced enhancement in the lactate dehydrogenase activity of the subendocardium (p less than 0.001 vs subepicardium). These results show greater subendocardial than subepicardial oxidation rates of certain substrates in the normal heart. These results also suggest that the myocardium adapts to increased work by increasing the subendocardial oxidation rate of some but not all substrates, indicating further that there may be qualitative mitochondrial differences in the different regions of the heart.

Animals↗
PubMed1991

In vitro stimulation of glucose utilization by insulin in primary cultures of rat hepatocytes.

The effect of glucose concentration and insulin on glucose incorporation was studied in primary cultures of rat hepatocytes. The rate of glucose incorporation into hepatocytes was proportional to the medium glucose concentration from 100 to 800 mg/dl. At 800 mg/dl glucose the rate reached a plateau. Of the glucose taken up by hepatocytes, 16 and 18% was incorporated into glycogen and lipid, respectively, and 58% into the nucleotide fraction after incubation for 4 h. In the medium, lactate was the major product found. Insulin stimulates glucose incorporation by 20-112% into all the above pathways at glucose concentrations between 100 and 800 mg/dl. The insulin effect was noted as early as 2-4 h (early effect) and up to 24 h (delayed effect). This effect of insulin was observed to be dose dependent from 5 to 200 ng/ml insulin. While the delayed insulin effect was abolished by cycloheximide, the early effect of insulin was not affected. With respect to the key enzyme activities of glucose utilization, activation of glycogen synthase (increase of I-activity/total activity) and pyruvate kinase (activation at 0.2 mM phosphoenolpyruvate) was noted 4 h after insulin addition, and these effects were not abolished by cycloheximide. These two enzymes increased in total activity after 24 h. Both glucokinase and glucose-6-phosphate dehydrogenase activities increased by 30-35% and 65-93% at 4 and 24 h, respectively. The results indicate that hepatocytes directly utilize glucose in a dose-dependent manner with respect to glucose and insulin. A major early and delayed effect of insulin appeared due to the activation and induction of the key hepatic enzymes of glucose utilization, respectively.

Animals↗
PubMedDate not supplied

[The mechanism of acetate assimilation in purple nonsulfur bacteria lacking the glyoxylate pathway: enzymes of the citramalate cycle in Rhodobacter sphaeroides].

The mechanism of acetate assimilation by the purple nonsulfur bacterium Rhodobacter sphaeroides, which lacks the glyoxylate shortcut, has been studied. In a previous work, proceeding from data on acetate assimilation by Rba. sphaeroides cell suspensions, a suggestion was made regarding the operation, in this bacterium, of the citramalate cycle. This cycle was earlier found in Rhodospirillum rubrum in the form of an anaplerotic reaction sequence that operates during growth on acetate instead of the glyoxylate shortcut, which is not present in the latter bacterium. The present work considers the enzymes responsible for acetate assimilation in Rba. sphaeroides. It is shown that this bacterium possesses the key enzymes of the citramalate cycle: citramalate synthase, which catalyzes condensation of acetyl-CoA and pyruvate and, as a result, forms citramalate, and 3-methylmalyl-CoA lyase, which catalyzes the cleavage of 3-methylmalyl-CoA to glyoxylate and propionyl-CoA. The regeneration of pyruvate, which is the acetyl-CoA acceptor in the citramalate cycle, involves propionyl-CoA and occurs via the following reaction sequence: propionyl-CoA (+ CO2) --> methylmalonyl-CoA --> succinyl-CoA --> succinate --> fumarate --> malate --> oxalacetate (- CO2) --> phosphoenolpyruvate --> pyruvate. The independence of the cell growth and the acetate assimilation of CO2 is due to the accumulation of CO2/HCO3- (released during acetate assimilation) in cells to a level sufficient for the effective operation of propionyl-CoA carboxylase.

Acetates↗
PubMed2006

Effect of DHA supplementation on digestible starch utilization by rainbow trout.

Rainbow trout has a limited ability to utilize digestible carbohydrates efficiently. Trout feeds generally contain high levels of DHA, a fatty acid known to inhibit a number of glycolytic and lipogenic enzymes in animals. A study was conducted to determine whether carbohydrate utilization by rainbow trout might be affected by dietary DHA level. Two low-carbohydrate (<4 % digestible carbohydrate) basal diets were formulated to contain 1 (adequate) or 4 (excess) g/100 g DHA diet respectively. The two basal diets were diluted with increasing levels of digestible starch (0 %, 10 %, 20 % and 30 %, respectively) to produce eight diets. These diets were fed to fish for 12 weeks at 15 degrees C according to a pair-fed protocol that consisted of feeding the same amount of basal diet but different amounts of starch. Live weight, N and lipid gains, hepatic glycogen and plasma glucose values significantly increased, whereas feed efficiency (gain:feed) significantly decreased, with increasing starch intake (P<0.05). The retention efficiency of N (N gain/digestible N intake) improved with starch supplementation but was not affected by DHA level (P>0.05). Starch increased the activity of glucokinase, pyruvate kinase, glucose 6-phosphate dehydrogenase and fatty acid synthase (P<0.05) but did not affect hexokinase and malic enzyme activity. DHA had no effect on growth but increased plasma glucose and reduced carcass lipid and liver glycogen contents (P<0.05). Glycolytic and lipogenic enzymes were not affected by DHA level, except for pyruvate kinase, which was reduced by increasing DHA level. These results suggest only a marginal effect of dietary DHA on the ability of fish to utilize carbohydrate.

Animal Feed↗
PubMed2001

Involvement of a unique carbohydrate-responsive factor in the glucose regulation of rat liver fatty-acid synthase gene transcription.

Refeeding carbohydrate to fasted rats induces the transcription of genes encoding enzymes of fatty acid biosynthesis, e.g. fatty-acid synthase (FAS). Part of this transcriptional induction is mediated by insulin. An insulin response element has been described for the fatty-acid synthase gene region of -600 to +65, but the 2-3-fold increase in fatty-acid synthase promoter activity attributable to this region is small compared with the 20-30-fold induction in fatty-acid synthase gene transcription observed in fasted rats refed carbohydrate. We have previously reported that the fatty-acid synthase gene region between -7382 and -6970 was essential for achieving high in vivo rates of gene transcription. The studies of the current report demonstrate that the region of -7382 to -6970 of the fatty-acid synthase gene contains a carbohydrate response element (CHO-RE(FAS)) with a palindrome sequence (CATGTGn(5)GGCGTG) that is nearly identical to the CHO-RE of the l-type pyruvate kinase and S(14) genes. The glucose responsiveness imparted by CHO-RE(FAS) was independent of insulin. Moreover, CHO-RE(FAS) conferred glucose responsiveness to a heterologous promoter (i.e. l-type pyruvate kinase). Electrophoretic mobility shift assays demonstrated that CHO-RE(FAS) readily bound a unique hepatic ChoRF and that CHO-RE(FAS) competed with the CHO-RE of the l-type pyruvate kinase and S(14) genes for ChoRF binding. In vivo footprinting revealed that fasting reduced and refeeding increased ChoRF binding to CHO-RE(FAS). Thus, carbohydrate responsiveness of rat liver fatty-acid synthase appears to require both insulin and glucose signaling pathways. More importantly, a unique hepatic ChoRF has now been shown to recognize glucose responsive sequences that are common to three different genes: fatty-acid synthase, l-type pyruvate kinase, and S(14).

Animals↗
PubMed1991

Ammonia assimilation and glutamate incorporation in coenzyme F420 derivatives of Methanosarcina barkeri.

Methanosarcina barkeri was able to grow on L-alanine and L-glutamate as sole nitrogen sources. Cell yields were 0.5 g/l and 0.7 g/l (wet wt), respectively. The mechanism of ammonia assimilation in Methanosarcina barkeri strain MS was studied by analysis of enzyme activities. Activity levels of nitrogen-assimilating enzymes in extracts of cells grown on different nitrogen sources (ammonia, 0.05-100 mM; L-alanine, 10 mM; L-glutamate, 10 mM) were compared. Activities of glutamate dehydrogenase, glutamate synthase, glutamine synthetase, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase could be measured in cells grown on these three nitrogen sources. Alanine dehydrogenase was not detected under the growth conditions used. None of the measured enzyme activities varied significantly in response to the NH4+ concentration. The length of the poly-gamma-glutamyl side chain of F420 derivatives turned out to be independent of the concentration of ammonia in the culture medium.

Alanine↗
PubMed1999

Glucose protection from MPP+-induced apoptosis depends on mitochondrial membrane potential and ATP synthase.

MPP+ inhibits mitochondrial complex I and alpha-ketoglutarate dehydrogenase causing necrosis or apoptosis of catecholaminergic neurons. Low glucose levels or glycolytic blockade has been shown to potentiate MPP+ toxicity. We found that MPP+ caused concentration-dependent apoptosis of neuronally differentiated PC12 cells and that glucose, but not pyruvate, supplementation reduced apoptosis. Oligomycin concentrations sufficient to inhibit ATP synthase blocked the decreased apoptosis afforded by glucose supplementation. Laser-scanning confocal microscope imaging of chloromethyl-tetramethylrosamine methyl ester fluorescence to estimate DeltaPsiM showed that MPP+ and atractyloside reduced DeltaPsiM, while cyclosporin A (CSA) and glucose supplementation reversed decreases in DeltaPsiM caused by MPP+. Oligomycin blocked the effect of glucose supplementation on DeltaPsiM. These findings show that (i) MPP+-induced and atractyloside-induced apoptosis are associated with reduced DeltaPsiM; (ii) CSA maintains DeltaPsiM and reduces MPP+-induced apoptosis; and (iii) glucose supplementation maintains DeltaPsiM, likely by glycolytic ATP-dependent proton pumping at ATP synthase and reduces MPP+-induced apoptosis.

1-Methyl-4-phenylpyridinium↗
PubMed1998

Biosynthesis of lipoic acid in Arabidopsis: cloning and characterization of the cDNA for lipoic acid synthase.

Lipoic acid is a coenzyme that is essential for the activity of enzyme complexes such as those of pyruvate dehydrogenase and glycine decarboxylase. We report here the isolation and characterization of LIP1 cDNA for lipoic acid synthase of Arabidopsis. The Arabidopsis LIP1 cDNA was isolated using an expressed sequence tag homologous to the lipoic acid synthase of Escherichia coli. This cDNA was shown to code for Arabidopsis lipoic acid synthase by its ability to complement a lipA mutant of E. coli defective in lipoic acid synthase. DNA-sequence analysis of the LIP1 cDNA revealed an open reading frame predicting a protein of 374 amino acids. Comparisons of the deduced amino acid sequence with those of E. coli and yeast lipoic acid synthase homologs showed a high degree of sequence similarity and the presence of a leader sequence presumably required for import into the mitochondria. Southern-hybridization analysis suggested that LIP1 is a single-copy gene in Arabidopsis. Western analysis with an antibody against lipoic acid synthase demonstrated that this enzyme is located in the mitochondrial compartment in Arabidopsis cells as a 43-kD polypeptide.

Amino Acid Sequence↗
PubMed2005

Tricarboxylic acid cycle inhibition by Li+ in the human neuroblastoma SH-SY5Y cell line: a 13C NMR isotopomer analysis.

Li+ effects on glucose metabolism and on the competitive metabolism of glucose and lactate were investigated in the human neuroblastoma SH-SY5Y cell line using 13C NMR spectroscopy. The metabolic model proposed for glucose and lactate metabolism in these cells, based on tcaCALC best fitting solutions, for both control and Li+ conditions, was consistent with: (i) a single pyruvate pool; (ii) anaplerotic flux from endogenous unlabelled substrates; (iii) no cycling between pyruvate and oxaloacetate. Li+ was shown to induce a 38 and 53% decrease, for 1 and 15 mM Li+, respectively, in the rate of glucose conversion into pyruvate, when [U-13C]glucose was present, while no effects on lactate production were observed. Pyruvate oxidation by the tricarboxylic acid cycle and citrate synthase flux were shown to be significantly reduced by 64 and 84% in the presence of 1 and 15 mM Li+, respectively, suggesting a direct inhibitory effect of Li+ on tricarboxylic acid cycle flux. This work also showed that when both glucose and lactate are present as energetic substrates, SH-SY5Y cells preferentially consumed exogenous lactate over glucose, as 62% of the acetyl-CoA was derived from [3-13C]lactate while only 26% was derived from [U-13C]glucose. Li+ did not significantly affect the relative utilisation of these two substrates by the cells or the residual contribution of unlabelled endogenous sources for the acetyl-CoA pool.

Acetyl Coenzyme A↗
PubMed1980

Cysteine synthesis by Desulfovibrio vulgaris extracts.

Extracts of Desulfovibrio vulgaris were found to contain serine transacetylase and cysteine synthase activities. When extracts were incubated with bisulfite and o-acetylserine, or acetyl coenzyme A plus L-serine, under a hydrogen atmosphere, cysteine was formed. Pyruvate served as a reductant for bisulfite reduction to sulfide and concomitantly provided the acetyl moiety for acetyl coenzyme A formation. Consequently, when extracts were incubated with pyruvate, bisulfite, and L-serine, cysteine synthesis resulted.

Acetyl Coenzyme A↗
PubMed1999

The Arabidopsis thaliana dhdps gene encoding dihydrodipicolinate synthase, key enzyme of lysine biosynthesis, is expressed in a cell-specific manner.

Lysine synthesis in prokaryotes, some phycomycetes and higher plants starts with the condensation of L-aspartate-beta-semialdehyde (L-ASA) and pyruvate into dihydrodipicolinic acid. The enzyme that catalyses this step, dihydrodipicolinate synthase (DHDPS), is inhibited by the end-product lysine and is therefore thought to have a regulatory control on lysine synthesis. We have cloned and sequenced an Arabidopsis thaliana DNA fragment containing 900 bases upstream of the dhdps coding sequence. A transcriptional fusion of this fragment with the beta-glucuronidase reporter gene (uidA. Gus) was used to study the transcription properties of this promoter fragment (DS). No lysine-induced repression on transcription could be detected. Expression of DS-Gus activity in transformed Arabidopsis thaliana and Nicotiana tabacum was found to be cell type-specific. In the vegetative parts of the plant, GUS activity was located in meristems and young vasculature of roots, in vasculature of stem and leaves and in the meristems of young shoots. In flowers, high expression was found in the carpels, style, stigma, developing embryos, tapetum of young anthers and pollen. We demonstrated that the Arabidopsis DS promoter can direct its cell type-specific expression in a heterologous plant, Nicotiana tuabacum. The importance of transcriptional regulation of the dhdps gene, and in more general genes involved in amino acid biosynthesis, is discussed.

Amino Acid Sequence↗