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At least 559 records · Page 31Linked to original sources
PubMed1986

Induction of corticosteroid biosynthetic pathway by ACTH and high-density lipoprotein in newborn rat adrenocortical cells cultured in serum-free medium.

In order to investigate the role of rat high-density lipoprotein (HDL) on adrenal cholesterol accumulation and steroidogenic pathways (corticosteroid, i.e., 21-hydroxysteroid biosynthesis and reductive metabolism of progesterone), newborn rat adrenal cells cultured in serum-free medium were used. Incubation of [4-14C]cholesterol-HDL in serum-free medium compared to those in medium with lipoprotein-deficient serum, in serum-free medium with ACTH compared to those without ACTH, both showed an increase of labelled cholesterol in cells and of labelled 21-hydroxysteroids excreted in medium. Substitution of serum-supplemented medium by serum-free and cholesterol-free medium led to a deep decrease of ACTH-induced steroid biosynthesis with a predominance of 20 alpha-reduced steroids; addition of HDL restored the corticosteroid biosynthesis and decreased the reductive metabolism. Addition of increased concentrations of HDL (7-150 micrograms cholesterol/ml) enhanced, in a saturable fashion, the total cholesterol uptake and the corticosteroid biosynthesis. The total cholesterol accumulation in cells exceeded by 4-fold the steroid production at saturation. The ratio between the two steroidogenic pathways increased up to 40 at saturation in favor of corticosteroids. These results suggest that HDL is at least partly internalized and that probably its constituents contribute greatly to the control of the two different steroidogenic pathways.

Adrenal Cortex↗
PubMed1976

Effect of lead on some parameters of the heme biosynthetic pathway in rat tissues in vivo.

Lead was administered to male and female rats in drinking water for 3 and 6 weeks at the following doses: 0, 10, 100, 1000, 5000 ppm and for 6 months at 10 ppm only. Various parameters of blood - lead concentration (Pb-B), hematocrit (Htc), hemoglobin (Hb), free erythrocyte porphyrins (FEB), delta-aminolevulinate dehydratase (ALAD), reticulocytes - and tissue - ALAD, free tissue porphyrins (FTP), lead concentration (Pb-T) - were determined. Pb-B increases with dose but reaches rapidly a plateau despite continuous Pb administration. Concentration of Pb in kidney, liver and brain correlates with Pb-B. Pb does not accumulate in heart. Kidney is the main site of Pb deposition and kidney ALAD is the parameter most susceptible to lead, since reduction is observed in all treated groups after 3 weeks of exposure. However, kidney ALAD inhibition is transitory since after 6 weeks it is only observed in the 5000 ppm group. At 10 ppm lead prevents also the increase in blood ALAD activity normally associated with the reticulocytosis of repetitive bleeding. The next parameters affected by lead are: ALAD in blood which is inhibited after 6 weeks of treatment with 100 ppm lead, and FEP, delta-aminolevulinic acid plus other pyrrole-forming substances in urine (ALA-U), and FTP in kidney which are increased after 3 or 6 weeks of treatment with 1000 and 5000 ppm lead.

Aminolevulinic Acid↗
PubMed1993

Genetic engineering of commercially useful biosynthetic pathways in transgenic plants.

In many economically important plant species, the chemical composition of one or more non-protein compounds determines the value of the plant and may have an important role in protecting the plant from environmental stress, including pests, drought, salt, temperature and light. A number of potential opportunities exist whereby the range or amount of such valuable compounds can be increased by genetic engineering.

Carbohydrates↗
PubMed1992

Kinetic evidence for separate 3 beta-hydroxysteroid dehydrogenase-isomerases in androgen and 16-androstene biosynthetic pathways in the pig testis.

The microsomal fraction from the testes of immature pigs (less than 1 week old) contains 3 beta-hydroxysteroid dehydrogenase-isomerase (3 beta-HSD-isomerase) activities that convert dehydroepiandrosterone (DHA) to 4-androstenedione and 5,16-androstadien-3 beta-ol (andien-beta) to 4,16-androstadien-3-one (dienone). These reactions are necessary for the biosynthesis of hormonally and pheromonally active steroids. Kinetic analyses of these activities were done to determine whether they are catalysed by a single enzyme or if there is any interaction between the substrates and products of one reaction on the activity of the other enzyme. Kinetic parameters were determined and the affinities for steroid substrate were similar (7-9 mumol/l) but the Vmaxapp value for the conversion of andien-beta to dienone was 10-fold that of the DHA to 4-androstenedione reaction. In analyses of the conversion of DHA to 4-androstenedione, neither andien-beta nor dienone inhibited the reaction and especially, no effect on the Kmapp for DHA was observed which would have indicated competition between DHA and andien-beta for the same active site (Kiapp from slope and intercept replots were between 3 and 80 times the values of the kinetic constants). Similarly, DHA and 4-androstenedione had minor or negligible effects on the conversion of andien-beta to dienone (Kiapp from slope replots were the same as the Kmapp but the Kiapp from the intercept replot was 12 to 25% of the Vmaxapp). It is concluded that substrate specific 3 beta-HSD-isomerases for andien-beta and DHA exist in the immature pig testis and there is little, if any interaction between these enzymes.

Androgens↗
PubMed1992

Phospholipases modulate immature pig testicular androgen and 16-androstene biosynthetic pathways in vitro.

The role of membrane phospholipids in porcine testicular androgen and 16-androstene biosynthesis was examined by monitoring the effects of phospholipase treatments on the activities of the steroid transforming enzymes. Untreated (control) microsomes from immature pig testes converted pregnenolone to 17-hydroxypregnenolone and DHA to 5,16-androstadien-3 beta-ol (andien-beta) and 4,16-androstadien-3-one (dienone) in the 16-androstene pathway, these metabolites accounting for most (65%) of the pregnenolone converted. The 4-ene steroids in the androgen pathway (progesterone, 17-hydroxyprogesterone, androstenedione and testosterone) totalled less than 10% of the pregnenolone metabolites. No estrogens or 5 alpha-reduced metabolites were detected. Treatment with phospholipase A2 or C, decreased the conversion of pregnenolone to 4-ene-3-oxo steroids but did not decrease the quantities of 5-ene-3 beta-hydroxysteroids. Confirmation of these findings was obtained by measuring the individual enzymatic steps. Phospholipases A2 and C significantly reduced the conversion of DHA to androstenedione and andien-beta to dienone but did not affect 17-hydroxylase or 'andien-beta-synthetase'. However, when the C-17, 20 lyase step was measured alone, phospholipase C decreased the quantity of androstenedione produced indicating that the side-chain cleavage reaction may involve a lipid component. The different effects of phospholipases on these enzymes suggests that pregnenolone metabolism may be regulated by alterations in the membrane microenvironment.

Aldehyde-Lyases↗
PubMedDate not supplied

Combined action of inhibitors of polyamine biosynthetic pathway with a known antimalarial drug chloroquine on Plasmodium falciparum.

Difluoromethylornithine (alpha-DFMO), a specific enzyme activated inhibitor of ornithine decarboxylase activity, a bis (benzyl) polyamine analogue (MDL 27695) and chloroquine resulted in a dose-dependent inhibition of the parasite. The IC50 value of alpha-DFMO, MDL 27695 and chloroquine was 1.85 mM, 2.0 microM and 23 ng ml-1 respectively. The combined action of MDL 27695 (3 microM) and chloroquine (5 ng ml-1) on P. falciparum growth showed near additive effect, whereas the combination of alpha-DFMO (1.0 mM) and chloroquine (5 ng ml-1) was more than the effect of each drug individually but not additive. Similarly the combined effect of MDL 27695 (3 microM) and alpha-DFMO (1.0 mM) on P. falciparum growth was not additive. The effect of these inhibitors alone and in combination on polyamine biosynthesis is also reported.

Animals↗
PubMed2005

Synthesis and biological evaluation of N-[4-[5-(2,4-diamino-6-oxo-1,6-dihydropyrimidin-5-yl)-2-(2,2,2-trifluoroacetyl)pentyl]benzoyl]-L-glutamic acid as a potential inhibitor of GAR Tfase and the de novo purine biosynthetic pathway.

The synthesis and evaluation of N-[4-[5-(2,4-diamino-6-oxo-1,6-dihydropyrimidin-5-yl)-2-(2,2,2-trifluoroacetyl)pentyl]benzoyl]-L-glutamic acid (2) as an inhibitor of glycinamide ribonucleotide transformylase (GAR Tfase) and aminoimidazole carboxamide ribonucleotide transformylase (AICAR Tfase) are reported. The inhibitor 2 was prepared in a convergent synthesis involving C-alkylation of methyl 4-(4,4,4-trifluoro-3-dimethylhydrazonobutyl)benzoate with 1-chloro-3-iodopropane followed by construction of the pyrimidinone ring. Compound 2 was found to be an effective inhibitor of recombinant human GAR Tfase (K(i) = 0.50 microM), whereas it was inactive (K(i) > 100 microM) against E. coli GAR Tfase as well as recombinant human AICAR Tfase. Compound 2 exhibited modest, purine-sensitive growth inhibitory activity against the CCRF-CEM cell line (IC50 = 6.0 microM).

Antineoplastic Agents↗
PubMed2005

Design, synthesis, and biological evaluation of 10-methanesulfonyl-DDACTHF, 10-methanesulfonyl-5-DACTHF, and 10-methylthio-DDACTHF as potent inhibitors of GAR Tfase and the de novo purine biosynthetic pathway.

The synthesis and evaluation of 10-methanesulfonyl-DDACTHF (1), 10-methanesulfonyl-5-DACTHF (2), and 10-methylthio-DDACTHF (3) as potential inhibitors of glycinamide ribonucleotide transformylase (GAR Tfase) and aminoimidazole carboxamide ribonucleotide transformylase (AICAR Tfase) are reported. The compounds 10-methanesulfonyl-DDACTHF (1, K(i) = 0.23 microM), 10-methanesulfonyl-5-DACTHF (2, K(i) = 0.58 microM), and 10-methylthio-DDACTHF (3, K(i) = 0.25 microM) were found to be selective and potent inhibitors of recombinant human GAR Tfase. Of these, 3 exhibited exceptionally potent, purine sensitive growth inhibition activity (3, IC50 = 100 nM) against the CCRF-CEM cell line being 3-fold more potent than Lometrexol and 30-fold more potent than the parent, unsubstituted DDACTHF, whereas 1 and 2 exhibited more modest growth inhibition activity (1, IC50 = 1.0 microM and 2, IC50 = 2.0 microM).

Antineoplastic Agents↗
PubMed2006

L-Lysine biosynthetic pathway of Methylophilus methylotrophus and construction of an L-lysine producer.

Previously, we showed that the enzymes aspartokinase (AK) and dihydrodipicolinate synthase (DDPS), which are involved in L-lysine biosynthesis in the Gram-negative obligate methylotroph Methylophilus methylotrophus AS1, were inhibited by allosteric effectors, including L-lysine. To elucidate further the regulation of L-lysine biosynthesis in M. methylotrophus, we cloned the genes encoding three other enzymes involved in this pathway, L-aspartate-beta-semialdehyde dehydrogenase, dihydrodipicolinate reductase (DDPR) and diaminopimelate decarboxylase, and examined their properties. DDPR was markedly inhibited by L-lysine. Based on this and our previous results, we constructed an L-lysine-producing strain of M. methylotrophus by introducing well-characterized genes encoding desensitized forms of AK and DDPS, as well as dapB (encoding DDPR) from Escherichia coli, using a broad host range plasmid. L-Lysine production was significantly increased by employing an S-(2-aminoethyl)-L-cysteine (L-lysine analog)-resistant mutant as the host. This derivative accumulated L-lysine at a concentration of 1 g l(-1) of medium using methanol as a carbon source.

Aspartate-Semialdehyde Dehydrogenase↗
PubMed2003

Crystal structure of an Acyl-ACP dehydrogenase from the FK520 polyketide biosynthetic pathway: insights into extender unit biosynthesis.

Polyketide synthases (PKSs) synthesize the polyketide cores of pharmacologically important natural products such as the immunosuppressants FK520 and FK506. Understanding polyketide biosynthesis at atomic resolution could present new opportunities for chemo-enzymatic synthesis of complex molecules. The crystal structure of FkbI, an enzyme involved in the biosynthesis of the methoxymalonyl extender unit of FK520, was solved to 2.1A with an R(crys) of 24.4%. FkbI has a similar fold to acyl-CoA dehydrogenases. Notwithstanding this similarity, the surface and substrate-binding site of FkbI reveal key differences from other acyl-CoA dehydrogenases, suggesting that FkbI may recognize an acyl-ACP substrate rather than an acyl-CoA substrate. This structural observation coincided the genetic experiment done by Carroll et al. J. Am. Chem. Soc., 124 (2002) 4176. Although an in vitro assay for FkbI remains elusive, the structural basis for the substrate specificity of FkbI is analyzed by a combination of sequence comparison, docking simulations and structural analysis. A biochemical mechanism for the role of FkbI in the biosynthesis of methoxymalonyl-ACP is proposed.

Acyl Coenzyme A↗
PubMed2005

Comparative non-radioactive RT-PCR assay: an approach to study the neurosteroids biosynthetic pathway in humans.

Polymerase chain reaction (PCR) is a powerful tool for qualitative evaluation of nucleic acid expression. PCR has been widely applied to measure DNA and RNA messages expression. Neurosteroids synthesized in the nervous system are potent modulators of synaptic activity and have been implicated in several neuropsychiatric disorders. To examine the possibility of an altered expression of the neurosteroidogenic metabolic enzymes in neurological diseases (like Parkinson's disease, PD) we developed a comparative non-radioactive RT-PCR assay to detect the mRNA levels of the peripheral benzodiazepine receptor, the 5alpha-reductase type 1 and 3alpha-hydroxysteroid-oxidoreductase type 1 and 2 in lymphocytes obtained from PD patients. The results were compared with that obtained from simultaneous quantification of progesterone, 5alpha-dihydroprogesterone and 3alpha,5alpha-tetrahydroprogesterone in the plasma and cerebro-spinal fluid of the same individuals using a gas chromatography mass spectrometry (GC/MS) technique. We found a significant decrease of the rate-limiting enzyme 5alpha-R1 along with a significant decrease in plasma and CSF of the 3alpha,5alpha-tetrahydroprogesterone and of the 5alpha-dihydroprogesterone. Comparative RT-PCR assay, along with complimentary techniques (i.e. GC/MS), has the sensitivity, selectivity and dynamic range to allow specific and reliable quantization of the enzymes involved in the neurosteroids pathway and represent a valuable tool to assess their expression in human neuropsychiatric conditions.

3-alpha-Hydroxysteroid Dehydrogenase (B-Specific)↗
PubMed2004

Effects of spermidine synthase overexpression on polyamine biosynthetic pathway in tobacco plants.

Transgenic tobacco plants overexpressing the Datura stramonium spermidine synthase (EC 2.5.1.16) cDNA were produced in order to understand the role of this gene in the polyamine metabolism and in particular in affecting spermidine endogenous levels. All the analysed transgenic clones displayed a high Level of overexpression of the exogenous cDNA with respect to the endogenous spermidine synthase. No relationship was detected between the mRNA expression level of S-adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.50), which did not change between the negative segregant control and the transgenic plants, and spermidine synthase, suggesting the existence of an independent regulatory mechanism for transcription of the two genes. The determination of enzyme activities indicated an increased spermidine synthase and S-adenosylmethionine decarboxylase activity, with the last being mainly recovered in the particulate fraction. ODC (ODC, EC 4.1.1.17) was the most active enzyme and its activity was equally distributed between the soluble and the particulate fraction, while ADC (ADC, EC 4.1.1.19) activity in the transgenic plants did not particularly change with respect to the controls. In comparison to the controls, the transformed plants displayed an increased spermidine to putrescine ratio in the majority of the clones assayed, white the total polyamine content remained almost unchanged. These findings suggest a high capacity of the transformed plants to tightly regulate polyamine endogenous levels and provide evidence that spermidine synthase is not a limiting step in the biosynthesis of polyamines.

Adenosylmethionine Decarboxylase↗
PubMed2005

Lovastatin alters the isoprenoid biosynthetic pathway in acute myelogenous leukemia cells in vivo.

Lovastatin, a competitive inhibitor of hydroxymethylglutaryl coenzyme A reductase (HMGR), is used therapeutically to lower plasma cholesterol levels and has garnered attention for its cytotoxic effects in leukemia cells. In this study, escalating doses of lovastatin were administered to nine patients with acute myelogenous leukemia. Peripheral blood leukemia cells were drawn pre- and post-lovastatin dosing. Plasma lovastatin bioactivity ranged up to 234 nM lovastatin equivalents. Our results show that in vivo lovastatin, at up to 200 mg/dose, induces an increased activity of leukemia cell HMGR and alters leukemia cell proliferation without discernibly altering Ras processing.

Adult↗