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At least 253 records · Page 14Linked to original sources
PubMed1993

Tissue-specific activity of pentose cycle oxidative enzymes during feeder lamb development.

Relationships between pentose cycle oxidative activity and differential fat growth were evaluated. Rambouillet wether lambs (n = 60) were slaughtered serially at 0, 40, 80, and 120 d on feed (15 lambs/group). Rack dissection and kidney fat weights were collected, and longissimus muscle i.m. fat content was determined. Postmortem longissimus muscle, s.c. fat, intermuscular fat (INT), and kidney fat (KP) samples were assayed in vitro for glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) activity (nanomoles.minute-1.gram of tissue-1), and samples were subjected to electrophoresis (PAGE) to separate tissue-specific isoforms. Allometric coefficients for rack components indicated that s.c. fat was the earliest-maturing, slowest-growing depot, INT was the latest-maturing, fastest-growing depot, and i.m. fat was intermediate (P < .05). Kidney fat grew faster than carcass weight and, as carcass weight increased, the growth rate of KP accelerated (P < .05). Enzyme activities increased until 40 d on feed and declined thereafter. Activities differed across tissues and time on feed end points (P < .05). Ratios of G6PDH:6PGDH, reflecting flux through the oxidative phase of the pentose cycle and, therefore, lipogenic activity, suggested growth patterns similar to those indicated by allometric analysis, except in the i.m. fat depot. Development of i.m. fat initially was intermediate to KP and INT, but G6PDH:6PGDH ratios increased with time on feed, suggesting a different regulatory mechanism and maturing pattern. Multiple forms of G6PDH were detected with PAGE, and although polymorphism was not detected, a tissue-specific isoform was isolated for INT fat.

Adipose Tissue↗
PubMed1978

A genetic approach to the biosynthesis of the rifamycin-chromophore in Nocardia mediterranei. I. Isolation and characterization of a pentose-excreting auxotrophic mutant of Nocardia mediterranei with drastically reduced rifamycin production.

The mutant under study, designated A8, is derived from a Nocardia mediterranei strain, N813, which is a high rifamycin B producer. A8 is auxotrophic for aromatic amino acids and produces much less rifamycin B than the parent. A mixture of pentoses with D (--) ribulose as the main product is accumulated in the fermentation broth of this mutant. It was shown to be affected in its transketolase activity as no formation of D-sedoheptulose -7P from pentose-phosphates could be detected in vitro using crude extracts. The only pathway so far known which is derived from D-sedoheptulose-7P is the shikimate pathway leading to aromatic amino acids and vitamins. Biochemical and genetic investigations with mutant A8, which is defective in both the biosynthesis of rifamycins and the biosynthesis of shikimate pathway products, show that the seven-carbon amino unit of the rifamycin-chromophore must be derived from an intermediate of the shikimate pathway.

Culture Media↗
PubMed2000

Transforming growth factor beta2 promotes glucose carbon incorporation into nucleic acid ribose through the nonoxidative pentose cycle in lung epithelial carcinoma cells.

The invasive transformation of A-459 lung epithelial carcinoma cells has been linked to the autocrine regulation of malignant phenotypic changes by transforming growth factor beta (TGF-beta). Here we demonstrate, using stable 13C glucose isotopes, that the transformed phenotype is characterized by decreased CO2 production via direct glucose oxidation but increased nucleic acid ribose synthesis through the nonoxidative reactions of the pentose cycle. Increased nucleic acid synthesis through the nonoxidative pentose cycle imparts the metabolic adaptation of nontransformed cells to the invasive phenotype that potentially explains the fundamental metabolic disturbance in tumor cells: highly increased nucleic acid synthesis despite hypoxia and decreased glucose oxidation.

Adenocarcinoma↗
PubMedDate not supplied

[Dependence of the initial stages of the pentose phosphate cycle on vitamin C metabolism in connective tissue pathology].

Correlation between rates of oxidative and non-oxidative steps of the pentose phosphate pathway and vitamin C concentration was studied in experimental diffuse impairment of connective tissue. As compared with transketolase, activity of glucose-6-phosphate dehydrogenase was more closely dependent on concentration of ascorbic acid. Content of vitamin C was considerably altered in tissues thus demonstrating profound deterioration of vitamin C metabolism under these conditions. Simultaneous impairment of the pentose phosphate pathway primary steps and of vitamin C metabolism appear to be responsible for initiation of the diffuse injury of the connective tissue.

Animals↗
PubMed1990

Computer simulation of the pentose-phosphate pathway and associated metabolism used in conjunction with NMR experimental data from human erythrocytes.

A computer-based model of the metabolism of sugar phosphates by human erythrocytes has been developed to assist in the understanding of the biochemical transformations occurring in the pentose phosphate pathway. These transformations are reflected in the changes, with time, of the relative intensities of the metabolite peaks apparent in 1H, 13C and 31P NMR spectra. The deterministic model consists of 79 reactions interconnected in a defined structure and characterized by 155 rate constants. It also includes 17 different enzymes, 69 enzyme forms, 32 metabolites, and initial value of time and concentration of each of the reactants. The differential equations describing the time-dependence of the concentrations of the reactants are generated and then solved by using the computer program BIOSSIM, which is designed to solve arrays of "stiff" differential equations. We synthesized [1-13C]D-ribose 5-phosphate and used 13C and 31P NMR to monitor its transformation into various intermediates of the pentose phosphate pathway, after the addition of diluted haemolysates which had previously been depleted of nicotinamide- and adenine-nucleotides. The concentrations of several of the reactants were able to be quantified, while other peaks in both the 13C and 31P spectra are yet to be assigned with confidence. There was reasonable qualitative agreement between some aspects of the computer simulation of the proposed metabolic system and the experimental data.

Biotransformation↗
PubMed1990

Elevated pentose cycle and glucuronyltransferase in daunorubicin-resistant P388 cells.

Anthracycline resistance of P388 daunorubicin-resistant cells cannot be accounted for merely by differences in drug uptake and retention; protection against intracellular drug was also indicated. Cytotoxicity of daunorubicin may be partially due to the formation of free radicals and reactive oxygen species (hydrogen peroxide, hydroxyl radical, singlet oxygen, and superoxide anion radical). Protection against free radicals and peroxides is largely dependent upon the availability of reduced glutathione, which in turn requires NADPH for its continual regeneration. Pentose phosphate cycle (also called hexose monophosphate shunt) is known to provide NADPH for maintenance of glutathione. Activities of the two NADPH-producing dehydrogenases of the cycle, glucose-6-phosphate and 6-phosphogluconate dehydrogenase, were 40% higher (P less than 0.05) and activity of the cycle in intact cells was 2-fold higher in the resistant than the sensitive cells. The cycle was as active in these cells as it is known to be in macrophages, indicating a very effective protection against oxidative stress, free radicals, and alkylating electrophiles. Elevated activity of the pentose phosphate pathway in drug-resistant cells can represent a mechanism of resistance against multiple structurally unrelated drugs. Efflux of daunorubicin may be aided by further metabolism to glucuronides. Daunorubicinol, a known active metabolite of daunorubicin, can be metabolized to a glucuronide by the cells and eliminated into the surrounding medium. Glucuronidation of daunorubicinol was evidenced by (a) release of daunorubicinol following glucuronidase hydrolysis of media from cell incubations with 1.8 microM daunorubicin and (b) production of radioactive glucuronide when cell homogenates were incubated with UDP-[14C]glucuronic acid plus daunorubicinol. Glucuronyltransferase activity with a broad substrate specificity was found in the cells. Using model substrates, 1-naphthol and o-aminophenol, it was determined that glucuronyltransferase activity was 4 times higher in daunorubicin-resistant than -sensitive P388 cells. Elevated glucuronyltransferase could contribute to daunorubicin and multidrug resistance.

Animals↗
PubMed1990

Epidermal growth factor and 12-O-tetradecanoylphorbol 13-acetate stimulate lactate production and the pentose phosphate pathway in freshly isolated rat hepatocytes.

Epidermal growth factor (EGF) and tetradecanoylphorbol acetate (TPA) rapidly stimulated the production of lactate by hepatocytes isolated from fed rats. Our results indicate that enzymes of both glycolysis and the pentose phosphate pathway are involved in these actions. EGF stimulated CO2 release from the 1-position of glucose, and caused a small but significant increase in pyruvate kinase activity. In addition, EGF caused a rise in fructose 1,6-bisphosphate and fructose 2,6-bisphosphate concentrations, indicating activation of phosphofructokinase. TPA did not alter the concentrations of these sugar phosphates, but did cause an increased lactate production and CO2 production from the 1-position of glucose similar to EGF. Furthermore, the EGF stimulation of lactate formation was independent of the presence of medium Ca2+. Phenylephrine stimulation of this process, in parallel incubations, was entirely dependent upon the presence of Ca2+ in the medium. We conclude that EGF stimulates glycolysis and the pentose phosphate pathway in isolated hepatocytes from fed rats. The duplication of these actions by TPA suggests that protein kinase C is a mediator of EGF action in hepatocytes.

Animals↗
PubMed1989

Structure elucidation of a senescence cross-link from human extracellular matrix. Implication of pentoses in the aging process.

Isolation and structure elucidation of an acid-resistant fluorescent molecule from human extracellular matrix revealed the presence of an imidazo[4,5-b]pyridinium molecule comprising a lysine and an arginine residue cross-linked by a pentose. Structure confirmation was achieved in vitro by the nonenzymatic reaction of ribose with lysine and arginine residues. The cross-link, named pentosidine, could also be synthesized with isomers of ribose, arabinose, xylose, and lyxose as well as by incubating young human collagen with these sugars at 37 degrees C. Pentosidine was found in a variety of human tissues including plasma proteins and red blood cells. Its presence in cells grown in culture strongly suggests ribose or ribonucleotide metabolites as precursors. The unexpected discovery of pentose-mediated protein cross-linking raises new questions concerning the aging process.

Aging↗
PubMed1989

[Features of glycolysis and pentose phosphate pathway in novobiocin sensitive and novobiocin resistant staphylococci].

Intensity of glycolysis and the pentose phosphate cycle in staphylococci sensitive and resistant to novobiocin was studied. The resistant variants did not practically store lactate and the activity of glycolytic enzymes i.e. hexokinase and aldolase was lowered by 15-20 and 53-59 per cent, respectively. Monoiodoacetate, a glycolysis inhibitor suppressed the glucose oxidation rate by 53.3-66.9 per cent in the sensitive variants and by 16-21.8 per cent in the resistant variants. At the same time it was characteristic of the resistant variants to increase the activity of the pentose phosphate cycle enzymes; glucose-6-phosphate dehydrogenase by 25-38.1 per cent transketolase by 21.5-27.3 per cent and transaldolase by 30-57.1 per cent. No differences in the transhydrogenase reaction kinetics of both the novobiocin sensitive and the novobiocin resistant variants were observed.

Drug Resistance, Microbial↗
PubMed1985

14C labelling of octulose bisphosphates by L-type pentose pathway reactions in liver in situ and in vitro.

The complete reaction sequence of the pentose pathway in vitro was studied by incubating [1-14C] ribose 5-phosphate with rat liver enzyme preparation and assessed by both the rate and extent of formation of the glucose 6-P product. The reactions formed, as intermediates, the 1,8-bisphosphates of D-glycero D-ido octulose (D-g D-i Oct) and D-glycero D-altro octulose, both heavily labelled at C-4 with 14C isotope during the 12h incubation. The formation of the octulose phosphates and the specificity of their isotopic labelling confirms an important prediction of, and contribution by reactions of the L-type pentose phosphate pathway (L-PP) in liver in vitro. Infusion in situ of [6-14C] glucose into the liver of the anaesthetized rabbit resulted in the formation of high specific activity [8-14C] D-g D-i Oct 1,8-P2. The specificity of labelling indicates that the octulose intermediate is formed according to the options of the L-PP mechanism of glucose metabolism in intact liver.

Animals↗
PubMed1984

[Dehydrogenases of the pentose cycle in rat liver peroxisomes].

Subcellular distribution of NADP+-dependent dehydrogenases of pentose phosphate pathway (glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase) in rat liver was studied, using differential and isopycnic centrifugation. The enzyme activity was detected in the purified peroxisomal fraction as well as in the cytosol. Both dehydrogenases are localized in the peroxisomal matrix. Administration of a hypolipidaemic drug clofibrate increases the amount of both enzymes in peroxisomes. The putative functional role of pentose phosphate cycle dehydrogenases in peroxisomes is discussed.

Animals↗
PubMedDate not supplied

[Enzymatic activity of pentose cycle and the contractile function of rabbit womb as dependent on the carbon dioxide level].

The in vitro experiments were carried out to study the electrical and mechanical activities of the myometrium of nonpregnant and pregnant female rabbits as well as the enzymic activity of the pentose cycle in this tissue as affected by changes in the concentration and a fixation degree of carbon dioxide. It is shown that an increase in the carbon dioxide concentration in the incubation medium decreases the enzymatic activity of nonoxidative unit of the pentose cycle, but has no effect on the carbon dioxide fixation, electrical and mechanical activity of the myometrium. The carbon dioxide fixation in the myometrium tissue during pregnancy is established to be intensified. A higher content of carbon dioxide in the medium weakens the womb with the tonic properties of prostaglandins being significantly deteriorated.

Animals↗
PubMedDate not supplied

Pentose phosphate pathway alterations in multi-drug resistant leukemic T-cells: 31P NMR and enzymatic studies.

31P NMR studies were carried out on the parental drug-sensitive human T-lymphoblastoid cell line CCRI-CEM (CEM) and its multi-drug-resistant (MDR) CEM-VBL100 variants, to assess the role of the pentose phosphate (PP) in MDR expression. CEM and CEM-VBL100 were incubated in the presence of 2-deoxyglucose, as recently proposed by our group (Clin. Chim. Acta 208: 39, 1992). Accumulation of 2-deoxyglucose 6-phosphate was much lower in the drug-resistant than in sensitive cells, indicating PP shunt activation in the MDR variants. This result was confirmed by enzymatic analyses, which demonstrated that, with respect to the parental line, the MDR variant was characterized by a) unaltered hexokinase activity; b) higher glucose 6-phosphate dehydrogenase activity; c) increased levels of reduced glutathione and marked increase of glutathione peroxidase activity after cell exposure to an oxidizing agent (tert-butylhydroperoxide). These results support the view that cell detoxification mechanisms mediated by the pentose phosphate pathway may contribute to the expression of MDR in tumours.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Enzymes of glycolytic and pentose phosphate pathways in cytosolic and leucoplastic fractions of developing seeds of Brassica campestris.

Distribution of the enzymes of glycolytic and pentose phosphate pathways were studied in cytosolic and leucoplastic fractions of the developing seeds of Brassica. Leucoplasts were isolated using a discontinuous percoll gradient. Intactness of leucoplasts was checked by ADP-glucose pyrophosphorylase assay in presence and absence of triton X-100. No contamination by microbodies, mitochondria and cytosol was observed as assessed by measuring the activities of marker enzymes. The recovery, latency and specific activity of each enzyme in different fractions were compared. The leucoplastic fraction contained complete set of the enzymes of glycolytic and pentose phosphate pathways, indicating that the two subcellular compartments metabolize carbon independently by these pathways. However, the enzymes showed higher activities in cytosolic fraction as compared to those in the leucoplasts, suggesting the need for exchange of metabolites in the two compartments through various translocators, for acting in cooperation to produce energy, reducing power and carbon skeletons for different biosynthetic activities in the non-photosynthetic plastids. Based on these compartmentation studies, a model for carbon flow for fatty acid synthesis in leucoplasts of developing Brassica seeds has been proposed.

Acetates↗
PubMedDate not supplied

Effect of diabetogenic nitrosourea on the activity of the pentose phosphate hunt in isolated islets.

The effect of streptozotocin (STZ) on the activity of the pentose phosphate shunt in islets was studied. Isolated rat islets were pre-incubated with glucose (1.7 mM) alone or with streptozotocin (STZ) or N-methyl-N-nitrosourea (MNU). The effects of these pretreatments on glucose metabolism and insulin secretion were assessed during subsequent incubation with either (1.14C), (6.14C). or (U.14C). glucose (16.7 mM) alone or plus phenazine methosulfate (PMS). Islets pretreated with STZ (1.5 mM) metabolized less (1.14C) and (U.14C). glucose. The order of inhibition by STZ of (14C)-glucose metabolism by islets was: (1.14C). greater than (U.14C). greater than (6.14C)-glucose. Whereas PMS (0.5 mM) increased the metabolism of both (U.14C). and (1.14C)-glucose, the metabolism of (6.14C)-glucose by STZ-pretreated islets was not increased by PMS. In a separate series of experiments, the total NADP+ + NADPH, but not the NAD content of the islets decreased after 2 min exposure of islets of STZ. At 30-min exposure, the levels of both pyridine coenzymes and that of 6-phosphogluconate were significantly decreased. The level of NADP+ + NADPH in islets was decreased more than the level of NAD. Insulin secretion was suppressed by the nitrosoureas. PMS (0.5 mM) increased the level of NADP+ + NADPH content of islets and augmented insulin secretion. It is concluded that the pentose phosphate pathway is inhibited on brief exposure of islets to STZ or MNU. Such inhibition may contribute to the suppression of insulin secretion caused by these nitrosoureas.

Animals↗
PubMed1991

Ethanolic fermentation of pentoses in lignocellulose hydrolysates.

In the fermentation of lignocellulose hydrolysates to ethanol, two major problems are encountered: the fermentation of the pentose sugar xylose, and the presence of microbial inhibitors. Xylose can be directly fermented with yeasts, such as Pachysolen tannophilus, Candida shehatae, and Pichia stipis, or by isomerization of xylose to xylulose with the enzyme glucose (xylose) isomerase (XI; EC 5.3.1.5), and subsequent fermentation with bakers' yeast, Saccharomyces cerevisiae. The direct fermentation requires low, carefully controlled oxygenation, as well as the removal of inhibitors. Also, the xylose-fermenting yeasts have a limited ethanol tolerance. The combined isomerization and fermentation with XI and S. cerevisiae gives yields and productivities comparable to those obtained in hexose fermentations without oxygenation and removal of inhibitors. However, the enzyme is not very stable in a lignocellulose hydrolysate, and S. cerevisiae has a poorly developed pentose phosphate shunt. Different strategies involving strain adaptation, and protein and genetic engineering adopted to overcome these different obstacles, are discussed.

Aerobiosis↗
PubMed1996

Effects of modifications in the pentose moiety and conformational changes on the binding of nucleoside ligands to uridine phosphorylase from Toxoplasma gondii.

One hundred and fifty analogues of uridine, with various modifications to the uracil and pentose moieties, have been tested and compared with uridine with respect to their potency to bind to uridine phosphorylase (UrdPase, EC 2.4.2.3) from Toxoplasma gondii. The effects of the alpha- and beta-anomers, the L- and D-enantiomers, as well as restricted syn and anti rotamers, on binding were examined. Pseudo-, lyxo-, 2,3'-anhydro-2'-deoxy-, 6,5'-cyclo-, 6,3'-methano-, O5',6-methano- and carbocyclic uridines did not bind to the enzyme. Ribosides bound better than the corresponding xylosides, which were better than the deoxyribosides. The binding of deoxyribosides was in the following manner: 2',3'-dideoxynucleosides > 2',5'-dideoxynucleosides > 2'-deoxyribosides > 3'- and 5'-deoxyribosides. alpha-2'-Deoxyribosides bound to the enzyme, albeit less tightly than the corresponding beta-anomers. The acyclo- and 2,2'-anhydrouridines bound strongly, with the 2,2'-anhydro-derivatives being the better ligands. 2,5'-Anhydrouridine bound to UrdPase less effectively than 2,2'-anhydrouridine and acyclouridine. Arabinosyluracil was at best a very poor ligand, but bound better if a benzyl group was present at the 5-position of the pyrimidine ring. This binding was enhanced further by adding a 5-benzyloxybenzyl group. A similar enhancement of the binding by increased hydrophobicity at the 5-position of the pyrimidine ring was observed with ribosides, alpha- and beta-anomers of the 2'-deoxyribosides, acyclonucleosides, and 2,2'-anhydronucleosides. Among all the compounds tested, 5-(benzyloxybenzyl)-2,2'-anhydrouridine was identified as the best ligand of T. gondii UrdPase with an apparent Ki value of 60 +/- 3 nM. It is concluded that the presence of an N-glycosyl bond is a prerequisite for a nucleoside ligand to bind to T. gondii UrdPase. On the other hand, the presence of a 2'-, 3'-, or 5'-hydroxyl group, or an N-glycosyl bond in the beta-configuration, enhanced but was not essential for binding. Furthermore, the potency of the binding of 2,2'-anhydrouridines (fixed high syn isomers) in contrast to the weaker binding of the 6,1'-anhydro- or 2,5'-anhydrouridines (fixed syn isomers), and the complete lack of binding of the 6,5'-cyclo, O5',6-methano- and 6,3'-methanouridines (fixed anti isomers) to T. gondii UrdPase indicate that the binding of ligands to this enzyme is in the syn/high syn conformation around the N-glycosyl bond. The results also indicate that the parasite but not the mammalian host UrdPase can participate in hydrogen bonding with N3 of the pyrimidine ring of nucleoside ligands. T. gondii UrdPase also has a larger hydrophobic pocket adjacent to the C5 of the pyrimidine moiety than the host enzyme, and can accommodate modifications in the pentose moiety which cannot be tolerated by the host enzyme. Most prominent among these modifications is the absence and/or lack of the ribo orientation of the 3'-hydroxyl group, which is a requirement for a ligand to bind to mammalian UrdPase. These differences between the parasite and host, enzymes can be useful in designing specific inhibitors or "subversive" substrates for T. gondii UrdPase.

Animals↗
PubMed1982

Regulation of pathways of glucose metabolism in kidney. Specific linking of pentose phosphate pathway activity with kidney growth in experimental diabetes and unilateral nephrectomy.

The pentose phosphate pathway operates at an elevated level in rat kidney following induction of diabetes and in the compensatory hypertrophy following unilateral nephrectomy in control and alloxan-diabetic rats, as shown by the yields of 14CO2 from [1-14C]glucose, [6-14C]glucose and 3H2O yields from [2-3H]glucose. The elevated flux through the pentose phosphate pathway is correlated with the increased RNA content and weight of the kidney. The direct utilization of NADPH for reductive synthetic reactions and the potential for indirect utilization via the sorbitol route and the linked transhydrogenase reactions of the glucuronate-xylulose pathway, for NADH and ATP generation, are also discussed.

Animals↗