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At least 559 records · Page 31Linked to original sources
PubMed1971

Evidence for cell-surface glycosyltransferases. Their potential role in cellular recognition.

Intact chicken embryo neural retina cells have been shown to catalyze the transfer of galactose-(14)C from uridine diphosphate galactose (UDP-galactose) to endogenous acceptors of high molecular weight as well as to exogenous acceptors. Four lines of evidence indicate that the galactosyltransferases catalyzing these reactions are at least partly located on the outside surface of the plasma membrane: (a) there is no evidence for appreciable uptake of sugar-nucleotides by vertebrate cells nor did unlabeled galactose, galactose 1-phosphate, or UDP-glucose interfere with the radioactivity incorporated during the reaction; (b) the cells remained essentially intact during the course of the reaction; (c) there was insufficient galactosyltransferase activity in the cell supernatants to account for the incorporation of galactose-(14)C into cell pellets; and (d) the intact cells could transfer galactose to acceptors of 10(6) daltons, and the product of this reaction was in the extracellular fluid. Appropriate galactosyl acceptors interfered with the adhesive specificity of neural retina cells; other compounds, which were not acceptors, had no effect. These results suggested that the transferase-acceptor complex may play a role in cellular recognition.

Amines↗
PubMed1982

Preliminary studies of the metabolic activity of purified suspensions of Mycobacterium leprae.

Mycobacterium leprae isolated from armadillo tissue incorporated radioactivity from D-(14C)glucose and (14C)protein hydrolysate. In the presence of glucose, the rate of incorporation of (14C)protein hydrolysate was increased. Uptake of glucose was inhibited by 2-deoxy-D-glucose and sodium azide; that of the amino acids was inhibited by puromycin and chloramphenicol and, weakly, by cycloheximide.

Amino Acids↗
PubMed1979

beta-1,3-Glucan in Developing Cotton Fibers: Structure, Localization, and Relationship of Synthesis to That of Secondary Wall Cellulose.

Evidence is presented for the existence of a noncellulosic beta-1,3-glucan in cotton fibers. The glucan can be isolated as distinct fractions of varying solubility. When fibers are homogenized rigorously in aqueous buffer, part of the total beta-1,3-glucan is found as a soluble polymer in homogenates freed of cell walls. The proportion of total beta-1,3-glucan which is found as the soluble polymer varies somewhat as a function of fiber age. The insoluble fraction of the beta-1,3-glucan remains associated with the cell wall fraction. Of this cell wall beta-1,3-glucan, a variable portion can be solubilized by treatment of walls with hot water, a further portion can be solubilized by alkaline extraction of the walls, and 17 to 29% of the glucan remains associated with cellulose even after alkaline extraction. A portion of this glucan can also be removed from the cell walls of intact cotton fibers by digestion with an endo-beta-1,3-glucanase. The glucan fraction which can be isolated as a soluble polymer in homogenates freed of cell walls is not associated with membranous material, and we propose that it represents glucan which is also extracellular but not tightly associated with the cell wall. Enzyme digestion studies indicate that all of the cotton fiber glucan is beta-linked, and methylation analyses and enzyme studies both show that the predominant linkage in the glucan is 1 --> 3. The possibility of some minor branching at C-6 can also be deduced from the methylation analyses. The timing of deposition of the beta-1,3-glucan during fiber development coincides closely with the onset of secondary wall cellulose synthesis. Kinetic studies performed with ovules and fibers cultured in vitro show that incorporation of radioactivity from [(14)C]glucose into beta-1,3-glucan is linear with respect to time almost from the start of the labeling period; however, a lag is observed before incorporation into cellulose becomes linear with time, suggesting that these two different glucans are not polymerized directly from the same substrate pool. Pulse-chase experiments indicate that neither the beta-1,3-glucan nor cellulose exhibits significant turnover after synthesis.

Journal Article↗
PubMed1982

Trehalose Toxicity in Cuscuta reflexa: Cell Wall Synthesis Is Inhibited upon Trehalose Feeding.

alpha,alpha-Trehalose induced a rapid blackening of the terminal 2.5-centimeter region of excised Cuscuta reflexa Roxb. vine. The incorporation of radioactivity from [(14)C]glucose into alkali-insoluble fraction of shoot tip was markedly inhibited by 12 hours of trehalose feeding to an excised vine. This inhibition was confined to the apical segment of the vine in which cell elongation occurred. The rate of blackening of shoot tip explants was hastened by the addition of gibberellic acid A(3), which promoted elongation growth of isolated Cuscuta shoot tips. The symptom of trehalose toxicity was duplicated by 2-deoxyglucose, which has been shown to be a potent inhibitor of cell wall synthesis in yeast. The observations suggest that trehalose interferes with the synthesis of cell wall polysaccharides, the chief component of which was presumed to be cellulose.

Journal Article↗
PubMed1985

Effect of path or sink anoxia on sugar translocation in roots of maize seedlings.

After feeding the scutellum of young maize seedlings with a labeled analog of glucose, 2-deoxy-d-glucose, the progress of radioactivity along the root was followed when either 70% of the path or the whole root were in strict anoxic conditions, and was compared with the translocation pattern of aerobic seedlings. Special care was taken to suppress the internal O(2) transport and to control its occurrence.In air, the radioactive compounds accumulated from 30 minutes in the root tip mainly as an analog of sucrose. When the whole root was anoxic, the progress of the radioactivity was very slow and never reached the tip which did not survive more than 8 hours. When 70% of the path was in strict anoxia and the sink (root tip) in air, the translocation was not impaired and the radioactivity accumulated in the tips as fast as in aerobic controls. The addition of 3 millimolar NaF, which inhibits the fermentative energy production, did not modify these results. It is concluded that long distance transport in maize sieve tubes has no special energy requirements and is controlled by source-sink relationships. The inhibition of sugar supply in anoxic root tips is attributed to an effect on unloading processes rather than on sink metabolism.

Journal Article↗
PubMed1987

Glucosyltransferase activity in human in vivo formed enamel pellicle and in whole saliva.

Two hour in vivo formed enamel pellicle samples and paraffin wax-stimulated saliva samples were collected from 10 volunteers for analyses of glycosyltransferase activity (GTF). GTF activity was recorded by monitoring incorporation of radioactivity from 14C-glucose labeled sucrose into glucan. Pellicle and saliva samples from all 10 subjects demonstrated GTF activity. The GTF activity in the pellicle samples was highest in subjects with high GTF activity producing adhesive glucan in saliva.

Dental Deposits↗
PubMed1976

Gluconeogenesis in infancy and childhood. II. Studies on the glucose production from alanine in three cases of persistent neonatal hypoglycaemia.

Gluconeogenesis was studied in 3 cases of persistent neonatal hypoglycaemia. In 2 of the cases the labelling of blood glucose after i.v. injection of 1415C-alanine was reduced. In these 2 patients only 1.3-5% of the injected radioactivity was recovered in blood glucose, compared with 10% in normoglycaemic patients. The labelling of glucose from 14C-glycerol, as studied in one case, was not reduced. In this patient the labelling of blood glucose from C-alanine was improved after subtotal resection of the pancreas, and with increasing age. By the time of the isotope studies the plasma insulin was normal in all patients, and no deficiency of glucagon secretion could be detected after stimulation with an alanine load. A quantitative amino acid analysis of plasma revealed a moderate increase of some of the glucogenic amino acids. The results were interpreted as a deficiency of gluconeogenesis, probably at the phosphoenolpyruvate carboxykinase or pyruvate carboxylase step.

Alanine↗
PubMed1978

Respiration correction for microbial heterotrophic activity assays that use tritium-labeled substrates.

Filtrates from microbial heterotrophic activity assay experiments in which tritiated glucose was used as a radioactively labeled substrate were collected, and their radioactivities were determined. These filtrates were subsequently evaporated to dryness to remove tritiated water generated by metabolism of the labeled glucose; the residue was suspended to original volume with distilled water, and the tritium levels were again assayed. In the water samples assayed, the amount of tritium label retained by the microorganism was about 75% of that respired.

Journal Article↗
PubMed1989

Optimal design of sampling schedules for studying glucose kinetics with tracers.

Minimum size sampling schedules for estimating glucose kinetic parameters from an impulsive (bolus) tracer injection in normal humans and rats are presented. Glucose kinetics are described by a two-compartment linear model, and reference values of the parameters are estimated from a data base with many samples. The optimal sampling schedule (OSS) is determined in each individual by using a D-optimal criterion and consists of four samples. A population optimal sampling schedule (POSS) applicable to all the individuals of a given population is then determined, and its reliability and efficiency in recovering kinetic parameters (e.g., rate constants, plasma clearance rate, and mean residence time) is assessed. The influence of model and measurement error on OSS is discussed. Moreover, the adoption of an enhanced POSS (EPOSS, 8 samples) is shown to improve accuracy and precision of parameter estimates in a predictable manner. Finally some suggestions are given for obtaining more information from turnover studies using a constant infusion of tracer, with or without a priming pulse of tracer.

Animals↗
PubMedDate not supplied

Effect of cold-exposure on rat organ blood flows.

Rat tissue blood flows and heart output were determined in adult Wistar rats under up to two hours of cold (4 degrees C) exposure, using radioactive 46Sc microspheres. Circulating glucose, lactate and triacylglycerol levels were also determined. Glucose concentrations increased with cold exposure in spite of the drainage of substrates induced by the activation of thermogenesis. Plasma triacylglycerol levels agree with a high involvement of fats in the sustenance of heat production. Cold-exposure had an immediate effect decreasing skin circulation, but increased that of muscle and brown adipose tissue. Kidney and intestine blood flows were maintained. In liver, blood flow increased progressively with cold-exposure. White adipose tissue showed--at first--low blood flow, but increased in parallel to that of liver. The data presented show a distribution of the blood in the body of the cold-exposed rat in which thermogenic responsibilities and supply of blood are evenly distributed throughout. The importance of haemodynamic changes in brown adipose tissue was considerable but the increased share of muscle blood flow suggests that it may have a global role in maintaining thermal homeostasis.

Adipose Tissue↗
PubMed1988

Metabolic activity in rat tectal grafts is influenced by host sensory innervation.

It has been shown previously that fetal tectal tissue grafted to the midbrain of newborn host rats grows, differentiates, and receives input from the host brain. In the present study, 4 neuroanatomical techniques have been combined to examine how metabolic activity in tectal transplants is influenced by an identified host sensory pathway. Tectal tissue from E15 pigmented rat embryos was transplanted to the midbrain region of anesthetized newborn rats of the same strain. Six to 22 weeks later, the functional relationship between tectal transplants and the visual system of the host animal was examined by mapping metabolic activity in the grafts and relating this activity to the presence or absence of host retinal innervation. Metabolic activity in tectal grafts was assessed using the radioactive 2-deoxy-glucose (2-DG) method and cytochrome oxidase (CO) histochemistry. Graft regions receiving input from host retinal axons were demonstrated by anterograde labeling after bilateral intraocular injections of HRP or WGA-HRP; all areas in grafts that were homologous to the superficial layers of normal superior colliculus (SC) were identified using AChE histochemistry. The levels of metabolic activity demonstrated with 2-DG and CO varied between animals and within individual grafts. Grafts that did not connect with the host showed only low metabolic activity. In grafts that received host input, localized areas of high metabolic activity were seen with both 2-DG and CO. Highest levels of activity were consistently found in area containing both intense AChE activity and a high density of host retinal innervation.

Animals↗
PubMed1966

Relationship between fatty acid and glucose utilization in Ehrlich ascites tumor cells.

Glucose greatly increased total free fatty acid (FFA) esterification by Ehrlich ascites tumor cells. However, the FFA concentration of the cells was not altered. Less exogenous FFA was oxidized to CO(2) at any given extracellular FFA:albumin molar ratio when glucose was available, but increasing amounts of radioactive CO(2) were produced as the FFA:albumin molar ratio was raised, even in the presence of glucose. It is suggested that glucose, by providing either energy or an excess of triose acceptor for fatty acid esterification, stimulated FFA uptake only indirectly, by increasing the utilization of FFA subsequent to initial uptake from the medium, i.e., by increasing the turnover rate of the cellular FFA pool. Availability of glucose decreased the oxidation of endogenous lipid radioactivity and the depletion of endogenous lipid ester radioactivity. Most of the radioactivity utilized was derived from phospholipids, and depletion of phospholipid radio-activity was spared when glucose was available. Depletion of cellular total lipid ester also was spared in the presence of glucose. Availability of FFA did not decrease total glucose uptake or its oxidation to CO(2). Glucose utilization by these cells appears not to be regulated by FFA availability in the manner that Randle and coworkers described for muscle.

Animals↗
PubMed1993

Is glycolysis impaired in erythrocytes of diabetic rats?

In erythrocytes from diabetic rats the generation of radioactive metabolites from 3H- or 14C-labeled D-glucose occurs at a lower rate than in cells from control animals, while the total production of L-lactic acid is the same in both cell types. The radioisotopic anomaly is not corrected by agents causing phosphofructokinase activation and is not attributable to interference of metabolites generated from either glycogen or 2,3-diphospho-D-glycerate. It is mimicked by preincubating the erythrocytes at a high concentration of D-glucose and suppressed in diabetic rats treated with insulin in order to lower the blood glucose concentration prior to sacrifice. These findings suggest isotopic dilution of the 3H- or 14C-labeled tracer by endogenous unlabeled D-glucose. The influence of factors such as the concentration of erythrocytes in the incubation medium, the concentration of extracellular D-glucose, and the length of incubation upon radioactive metabolic variables is also compatible with the postulated phenomenon of isotopic dilution.

1-Methyl-3-isobutylxanthine↗
PubMed1967

Microbial growth on C1 compounds. Uptake of [14C]formaldehyde and [14C]formate by methane-grown Pseudomonas methanica and determination of the hexose labelling pattern after brief incubation with [14C]methanol.

1. A study has been made of the incorporation of carbon from [(14)C]formaldehyde and [(14)C]formate by cultures of Pseudomonas methanica growing on methane. 2. The distribution of radioactivity within the non-volatile constituents of the ethanol-soluble fractions of the cells, after incubation with labelled compounds for periods of up to 1min., has been analysed by chromatography and radioautography. 3. Radioactivity was fixed from [(14)C]formaldehyde mainly into the phosphates of the sugars, glucose, fructose, sedoheptulose and allulose. 4. Very little radioactivity was fixed from [(14)C]formate; after 1min. the only products identified were serine and malate. 5. The distribution of radioactivity within the carbon skeleton of glucose, obtained from short-term incubations with [(14)C]methanol of Pseudomonas methanica growing on methane, has been investigated. At the earliest time of sampling over 70% of the radioactivity was located in C-1; as the time increased the radioactivity spread throughout the molecule. 6. The results have been interpreted in terms of a variant of the pentose phosphate cycle, involving the condensation of formaldehyde with C-1 of ribose 5-phosphate to give allulose phosphate.

Carbon Isotopes↗
PubMed1973

Glucose metabolism in the newborn rat. Hormonal effects in vivo.

1. The concentrations of liver glycogen and plasma d-glucose were measured in caesarian-delivered newborn rats at time-intervals up to 3h after delivery after treatment of the neonatal rats with glucagon, dibutyryl cyclic AMP, cortisol or cortisol+dibutyryl cyclic AMP. Glycogenolysis was promoted by glucagon or dibutyryl cyclic AMP in the third hour after birth but not at earlier times. Cortisol and dibutyryl cyclic AMP together (but neither agent alone) promoted glycogenolysis in the second hour after birth, but no hormone combination was effective in the first postnatal hour. 2. The specific radioactivity of plasma d-glucose was measured as a function of time for up to 75 min after the intraperitoneal injection of d-[6-(14)C]glucose and d-[6-(3)H]glucose into newborn rats at delivery and after treatment with glucagon or actinomycin D. Glucagon-mediated hyperglycaemia at this time was due to an increased rate of glucose formation and a decreased rate of glucose utilization. Actinomycin D prevented glucose formation and accelerated the rate of postnatal hypoglycaemia. 3. The specific radioactivity of plasma l-lactate and the incorporation of (14)C into plasma d-glucose was measured as a function of time after the intraperitoneal injection of l-[U-(14)C]lactate into glucagon- or actinomycin D-treated rats immediately after delivery. The calculated rates of lactate formation were unchanged by either treatment, but lactate utilization was stimulated by glucagon administration. Glucagon stimulated and actinomycin D diminished (14)C incorporation into plasma d-glucose. 4. The factors involved in the initiation of glycogenolysis and gluconeogenesis in the rat immediately after birth are discussed.

Animals↗