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At least 1,027 records · Page 57Linked to original sources
PubMed2005

Effect of hexoses and gonadotrophin supplementation on bovine oocyte nuclear maturation during in vitro maturation in a synthetic follicle fluid medium.

In vitro oocyte maturation (IVM) culture conditions have been relatively unchanged over the past few decades and remain suboptimal. In contrast, studies of the in vivo environment have led to significant improvements to in vitro embryo culture technologies. The aim of the present study was to determine the effect of maturing bovine cumulus-oocyte complexes (COCs) in medium based on the composition of bovine follicular fluid (Bovine VitroMat; Cook Australia, Eight Mile Plain, Qld, Australia). In particular, the effect of different glucose concentrations and glucosamine supplementation on meiotic maturation was determined. Culturing COCs in the presence of gonadotrophins in Bovine VitroMat, containing either physiological glucose concentrations (2.3 mM) or 5.6 mM (equivalent to levels in Tissue Culture Medium 199 (TCM199)) supplemented with glucosamine resulted in comparable cumulus expansion to COCs cultured in TCM199 plus gonadotrophins. However, nuclear maturation was 1.3-fold lower in Bovine VitroMat cultures containing 2.3 mM glucose compared with 5.6 mM glucose and this effect was independent of glucosamine supplementation. Investigations into the effects of different glucose concentrations and gonadotrophin supplementation during the initial 6 h of maturation demonstrated that COCs cultured in Bovine VitroMat with 5.6 mM glucose without gonadotrophins had a twofold acceleration of the rate of meiotic resumption, yet the rate of polar body formation was decreased by approximately 20% compared with cultures in 2.3 mM glucose and TCM199. However, this effect was not seen when COCs were cultured for the initial 16 h in Bovine VitroMat + 5.6 mM minus gonadotrophins or in Bovine VitroMat + 2.3 mM glucose +/- gonadotrophins. These data demonstrate that glucose concentrations and the timing of the introduction of gonadotrophin during IVM have variable effects on nuclear maturation. Manipulation of glucose concentrations may be a mechanism to influence oocyte meiotic progression and may lead to the development of improved IVM systems, allowing for an increased developmental capacity of bovine oocytes.

Animals↗
PubMed1999

Intraerythrocytic Plasmodium falciparum expresses a high affinity facilitative hexose transporter.

Asexual stages of Plasmodium falciparum cause severe malaria and are dependent upon host glucose for energy. We have identified a glucose transporter of P. falciparum (PfHT1) and studied its function and expression during parasite development in vitro. PfHT1 is a saturable, sodium-independent, and stereospecific transporter, which is inhibited by cytochalasin B, and has a relatively high affinity for glucose (Km = 0.48 mM) when expressed in Xenopus laevis oocytes. Competition experiments with glucose analogues show that hydroxyl groups at positions C-3 and C-4 are important for ligand binding. mRNA levels for PfHT1, assessed by the quantitative technique of tandem competitive polymerase chain reaction, are highest during the small ring stages of infection and lowest in gametocytes. Confocal immunofluorescence microscopy localizes PfHT1 to the region of the parasite plasma membrane and not to host structures. These findings have implications for development of new drug targets in malaria as well as for understanding of the pathophysiology of severe infection. When hypoglycemia complicates malaria, modeling studies suggest that the high affinity of PfHT1 is likely to increase the relative proportion of glucose taken up by parasites and thereby worsen the clinical condition.

Amino Acid Sequence↗
PubMed2001

Formation pathways for lysine-arginine cross-links derived from hexoses and pentoses by Maillard processes: unraveling the structure of a pentosidine precursor.

Covalently cross-linked proteins are among the major modifications caused by the advanced Maillard reaction. So far, the chemical nature of these aggregates and their formation pathways are largely unknown. Synthesis and unequivocal structural characterization are reported for the lysine-arginine cross-links N(6)-(2-([(4S)-4-ammonio-5-oxido-5-oxopentyl]amino)-5-[(2S,3R)-2,3,4- trihydroxybutyl]-3,5-dihydro-4H-imidazol-4-ylidene)-l-lysinate (DOGDIC 12), N(6)-(2-([(4S)-4-ammonio-5-oxido-5-oxopentyl]amino)-5-[(2S)-2,3-dihydroxypropyl]-3,5-dihydro-4H-imidazol-4-ylidene)-l-lysinate (DOPDIC 13), and 6-((6S)-2-([(4S)-4-ammonio-5-oxido-5-oxopentyl] amino)-6-hydroxy-5,6,7,7a-tetrahydro-4H-imidazo[4,5-b] pyridin-4-yl)-l-norleucinate (pentosinane 10). For these compounds, as well as for glucosepane 9 and pentosidine 11, the formation pathways could be established by starting from native carbohydrates, Amadori products, and 3-deoxyosones, respectively. Pentosinane 10 was unequivocally proven to be an important precursor of pentosidine 11, which is a well established fluorescent indicator for advanced glycation processes in vivo. The Amadori products are shown to be the pivots in the formation of the various cross-links 9-13. The bicyclic structures 9-11 are directly derived from aminoketoses, whereas 12 and 13 stem from reaction with the 3-deoxyosones. All products 9-13 were identified and quantified from incubations of bovine serum albumin with the respective 3-deoxyosone or carbohydrate. From these results it seems fully justified to expect both glucosepane 9 and DOGDIC 12 to constitute important in vivo cross-links.

Arginine↗
PubMed1984

Hexose transport and mucosal morphology in the small intestine of the zinc-deficient rat.

Immature male Wistar rats were given a zinc-depleted semi-synthetic diet (2 mg Zn/kg diet) for 4 weeks. Control groups received a similar diet containing 60 mg Zn/kg diet, either ad lib. or in amounts matched to the consumption of the Zn-deficient group. Rates of growth and food conversion efficiency were markedly lower in the Zn-deficient group compared to controls. The phloridzin-sensitive uptake of galactose and 3-O-methyl glucose by everted jejunal rings from each group was measured over a range of concentrations. Kinetic analysis revealed that the maximum transport rate (Vmax) for the uptake of both sugars was significantly higher in the Zn-deficient group than in the control groups. The villi, microdissected from samples of proximal jejunum, were significantly shorter and narrower across the base in the Zn-deficient group than those of the control groups, but were present in greater numbers per unit serosal area. The present study shows that Zn deficiency leads to significant morphological changes in rat small intestine, which are accompanied by an increase in the capacity of the tissue to take up sugars across the mucosal membrane.

3-O-Methylglucose↗
PubMed1974

The hexose-proton cotransport system of chlorella. pH-dependent change in Km values and translocation constants of the uptake system.

The proton concentration in the medium affects the maximal velocity of sugar uptake with a K(m) of 0.3 mM (high affinity uptake). By decreasing the proton concentration a decrease in high affinity sugar uptake is observed, in parallel the activity of a low affinity uptake system (K(m) of 50 mM) rises. Both systems add up to 100%. The existence of the carrier in two conformational states (protonated and unprotonated) has been proposed therefore, the protonated form with high affinity to 6-deoxyglucose, the unprotonated form with low affinity. A plot of extrapolated V(max) values at low substrate concentration versus proton concentration results in a K(m) for protons of 0.14 microM, i.e. half-maximal protonation of the carrier is achieved at pH 6.85. The stoichiometry of protons cotransported per 6-deoxyglucose is close to 1 at pH 6.0-6.5. At higher pH values the stoichiometry continuously decreases; at pH 8.0 only one proton is cotransported per four molecules of sugar. Whereas the translocation of the protonated carrier is strictly dependent on sugar this coupling is less strict for the unprotonated form. Therefore at alkaline pH a considerable net efflux of accumulated sugar can occur. The dependence of sugar accumulation on pH has been measured. The decrease in accumulation with higher pH values can quantitatively be explained by the decrease in the amount of protonated carrier. The properties of the unprotonated carrier resemble strikingly the properties of carrier at the inner side of the membrane. The inside pH of Chlorella was measured with the weak acid 5,5-dimethyl-2, 4-oxazolidinedion (DMO). At an outside pH of 6.5 the internal pH was found to be 7.2. To explain the extent of sugar accumulation it has to be assumed that the membrane potential also contributes to active sugar transport in this alga.

Biological Transport↗
PubMed1992

Feeding modulation by pentose and hexose analogues.

D-Glucosamine (GlcN), N-acetyl-D-glucosamine (GlcNAc) and 2,5-anhydro-D-mannitol (2,5-AM) were infused into the rat third cerebroventricle (icv) to compare their effects on food intake. GlcN (24 mumols/L) accelerated eating, and concomitantly increased plasma glucose, free fatty acids, and glycerol without affecting plasma insulin. GlcN accelerated lateral hypothalamic (LHA), and reciprocally decreased ventromedial hypothalamic (VMH) neuronal activity. Infusion of 12 mumols GlcNAc icv did not affect feeding, but oral administration (1200 mumols/L) induced feeding. The GlcNAc-induced feeding was completely abolished by bilateral truncal vagotomy. Infusion of 2,5-AM dose-dependently induced feeding (P less than 0.01). A maximal dose (24 mumols/L) did not substantially change plasma glucose or insulin. Unilateral 2,5-AM microinfusion (1.2 mumols/L) into the VMH, but not into the LHA, elicited feeding. The characteristic actions of these analogues are useful to clarify central control of food intake and also as probes to examine relations between feeding modulation and energy metabolism in the central nervous system.

Acetylglucosamine↗
PubMed1981

Stimulation of hexose uptake by human eosinophils with chemotactic factors.

The ability of several stimuli, all of which have been reported to stimulate eosinophil motility, to augment uptake or extracellular deoxyglucose (DOG), a glucose analogue, was studied. DOG uptake was stimulated in a concentration-dependent manner by the more potent chemotaxins--zymosan-activated serum, partially purified C5a. N-formyl-methionyl-leucyl-phenylalanine, and 5- and 11-hydroxyeicosatetraenoic acids. Less potent stimuli--the eosinophil chemotactic factor of anaphylaxis, histamine, and prostaglandin E2--did not stimulate DOG uptake. However, the correlation between the abilities of the agents to stimulate motility and DOG uptake was not completely uniform. Prostaglandin F2 alpha was a potent stimulant of DOG uptake yet is known to enhance only weakly chemokinesis and to be not chemotactic for eosinophils. The combined data from this and other studies indicate that these stimuli elicit specific and different sets of functional responses from eosinophils.

Arachidonic Acids↗
PubMed1992

Incorporation of hexose nucleoside analogues into oligonucleotides: synthesis, base-pairing properties and enzymatic stability.

Oligonucleotides containing 1-(2,4-dideoxy-beta-D-erythro-hexopyranosyl)thymine (2) and 1-(3,4-dideoxy-beta-D-erythro-hexopyranosyl)thymine (3) were synthesized on a solid support using the phosphoramidite approach. The properties of these oligonucleotides were compared with the earlier reported characteristics of oligonucleotides containing 1-(2,3-dideoxy-beta-D-erythro-hexopyranosyl) thymine (1). The order in enzymatic stability of end-substituted oligonucleotides is 3 greater than 1 much greater than 2. The hybridization properties of the modified oligonucleotides are in reverse order: 2 much greater than 1 greater than 3.

Alkaline Phosphatase↗
PubMed2002

Interactions of nitrate and CO2 enrichment on growth, carbohydrates, and rubisco in Arabidopsis starch mutants. Significance of starch and hexose.

Wild-type (wt) Arabidopsis plants, the starch-deficient mutant TL46, and the near-starchless mutant TL25 were grown in hydroponics under two levels of nitrate, 0.2 versus 6 mM, and two levels of CO(2), 35 versus 100 Pa. Growth (fresh weight and leaf area basis) was highest in wt plants, lower in TL46, and much lower in TL25 plants under a given treatment. It is surprising that the inability to synthesize starch restricted leaf area development under both low N (N(L)) and high N (N(H)). For each genotype, the order of greatest growth among the four treatments was high CO(2)/N(H) > low CO(2)/N(H), > high CO(2)/N(L), which was similar to low CO(2)/N(L). Under high CO(2)/N(L), wt and TL46 plants retained considerable starch in leaves at the end of the night period, and TL25 accumulated large amounts of soluble sugars, indicative of N-limited restraints on utilization of photosynthates. The lowest ribulose-1,5-bisphosphate carboxylase/oxygenase per leaf area was in plants grown under high CO(2)/N(L). When N supply is limited, the increase in soluble sugars, particularly in the starch mutants, apparently accentuates the feedback and down-regulation of ribulose-1,5-bisphosphate carboxylase/oxygenase, resulting in greater reduction of growth. With an adequate supply of N, growth is limited in the starch mutants due to insufficient carbohydrate reserves during the dark period. A combination of limited N and a limited capacity to synthesize starch, which restrict the capacity to use photosynthate, and high CO(2), which increases the potential to produce photosynthate, provides conditions for strong down-regulation of photosynthesis.

Arabidopsis↗
PubMed1998

Hexose transport in growing petunia pollen tubes and characterization of a pollen-specific, putative monosaccharide transporter.

We investigated the molecular and physiological processes of sugar uptake and metabolism during pollen tube growth and plant fertilization. In vitro germination assays showed that petunia (Petunia hybrida) pollen can germinate and grow not only in medium containing sucrose (Suc) as a carbon source, but also in medium containing the monosaccharides glucose (Glc) or fructose (Fru). Furthermore, high-performance liquid chromatography analysis demonstrated a rapid and complete conversion of Suc into equimolar amounts of Glc and Fru when pollen was cultured in a medium containing 2% Suc. This indicates the presence of wall-bound invertase activity and uptake of sugars in the form of monosaccharides by the growing pollen tube. A cDNA designated pmt1 (petunia monosaccharide transporter 1), which is highly homologous to plant monosaccharide transporters, was isolated from petunia. Pmt1 belongs to a small gene family and is expressed specifically in the male gametophyte, but not in any other vegetative or floral tissues. Pmt1 is activated after the first pollen mitosis, and high levels of mRNA accumulate in mature and germinating pollen. A model describing the transport of sugars to the style, the conversion of Suc into Glc and Fru, and the active uptake by a monosaccharide transporter into the pollen tube is presented.

Amino Acid Sequence↗
PubMed1987

Effects of nordihydroguaiaretic acid, phloretin, and phloridzin on the activity of adenylate cyclase, lipoxygenase and hexose transport, and growth of cultured keratinocytes.

Compounds related to the flavonoid group of natural products may have potential as antipsoriatic drugs. The dihydrochalcone phloretin, its glycoside derivative phloridzin, and the structurally related compound nordihydroguaiaretic acid (NDGA) were selected for study. Phloretin and NDGA strongly inhibited keratinocyte growth but had no effect on isoproterenol-stimulated adenylate cyclase; phloridzin had no effect on growth but potentiated the response of the enzyme. None had any effect on phosphodiesterase. Neither phloretin or phoridzin inhibited lipoxygenase or, surprisingly, decreased deoxyglucose transport. Phloretin and NDGA should be considered antipsoriatic agents.

Adenylyl Cyclases↗