Schistosoma mansoni: effects of in vitro serotonin (5-HT) on aerobic and anaerobic carbohydrate metabolism

The effect of Serotonin on carbohydrate metabolism, excreted end products, and adenine nucleotide pools in Schistosoma mansoni was determined following 60 min in vitro incubations under air (= 21% O2) and anaerobic (95% N2:5% CO2) conditions. In the presence of 0.25 mM Serotonin, glucose uptake increased by 82-84% and lactate excretion increased by 77-78%; levels of excreted lactate were significantly higher under aerobic than under anaerobic conditions. The tissue pools of glucose, hexosephosphates, fructose 1,6-bisphosphate, pyruvate, and lactate were significantly increased under anaerobic conditions compared to air incubation; the presence of Serotonin decreased tissue glucose pools and increased the size of the pyruvate and lactate tissue pools. The glycolytic carbon pool was significantly greater under anaerobic than under aerobic conditions, irrespective of Serotonin. Serotonin increased adenosine 5'-diphosphate and adenosine 5'-monophosphate levels under aerobic conditions; neither Serotonin nor gas phase significantly affected total adenine nucleotide levels or the adenylate energy charge. Serotonin increased energy requirements by S. mansoni due to increased muscle contractions; demand was met by enhanced rates of carbohydrate metabolism. Irrespective of gas phase, 74-78% of available carbohydrate was converted to lactate. In the presence of Serotonin, conversion of glucose to lactate was reduced to 63-67%. In view of the requirements by S. mansoni for an abundant supply of glycoprotein and glycolipid precursors for surface membrane renewal, it is suggested that carbohydrate (glucose and glycogen) that was not converted to lactate may have been incorporated into biosynthetic processes leading to membrane synthesis.     

Glycogen metabolism in resting and growing cells of Saccharomyces carlsbergensis

Saccharomyces carlsbergensis cells, growing under carbohydrate or nitrogen limitation, initially deplete their glycogen, which is resynthesized only during the late exponential phase. Cells, harvested in the carly exponential phase, are even unable to synthesize glycogen in glucose-containing phosphate buffer. This is in contrast to cells from the stationary phase which rapidly synthesize glycogen under the same conditions. Lack of O₂ slows down glycogen synthesis.Contrary to cells suspended in complete medium, addition of ammonia alone to nitrogen free-media induced neither breakdown of glycogen, nor complete cessation of glycogen synthesis. Ammonia slowed down glycogen synthesis (both aerobic and anaerobic), only, in cells grown either under carbohydrate or under nitrogen limitation.Glycogen synthesis was observed 1 min after addition of glucose to a starved cell suspension in phosphate buffer. Removal of the sugar from the buffer resulted in an instantanous decrease of the glycogen level in the cells. The results indicate that glycogen-metabolism is regulated by a variety of endogenous and environmental factors.     

Glycogen phosphorylase from Dictyostelium: a kinetic analysis by computer simulation.

A model of carbohydrate metabolism during differentiation in Dictyostelium discoideum has been used to investigate which enzyme kinetic mechanism(s) might be operative for glycogen phosphorylase in vivo. The model, which has been described previously, is capable of simulating experimentally observed changes in metabolite concentrations and fluxes during differentiation under both the standard starvation condition and in the presence of glucose (25 mM). The concentrations of saccharide end products of differentiation under these 2 conditions differ substantially.Glycogen phosphorylase is described in the model by a rapid equilibrium random bi bi mechanism and the effect of substituting 4 other kinetic mechanisms was examined. Each of these mechanisms in the model allows simulations compatible with the saccharide accumulation patterns found during differentiation in the absence of glucose. However, in the presence of glucose, only a reversible mechanism (random or ordered) is compatible with the experimental data. It is concluded that glycogen degradation in vivo is controlled by an enzyme catalyzing a reversible reaction, the rate of which is inversely related to the glucose-1-P concentration.     

Effect of carbohydrate supplementation on postexercise GLUT-4 protein expression in skeletal muscle.

The effect of carbohydrate supplementation on skeletal muscle glucose transporter GLUT-4 protein expression was studied in fast-twitch red and white gastrocnemius muscle of Sprague-Dawley rats before and after glycogen depletion by swimming. Exercise significantly reduced fast-twitch red muscle glycogen by 50%. During a 16-h exercise recovery period, muscle glycogen returned to control levels (25.0 +/- 1.4 micromol/g) in exercise-fasted rats (24.2 +/- 0. 3 micro). However, when carbohydrate supplementation was provided during and immediately postexercise by intubation, muscle glycogen increased 77% above control (44.4 +/- 2.1 micromol/g). Exercise-fasting resulted in an 80% increase in fast-twitch red muscle GLUT-4 mRNA but only a 43% increase in GLUT-4 protein concentration. Conversely, exercise plus carbohydrate supplementation elevated fast-twitch red muscle GLUT-4 protein concentration by 88% above control, whereas GLUT-4 mRNA was increased by only 40%. Neither a 16-h fast nor carbohydrate supplementation had an effect on fast-twitch red muscle GLUT-4 protein concentration or on GLUT-4 mRNA in sedentary rats, although carbohydrate supplementation increased muscle glycogen concentration by 40% (35.0 +/- 0.9 micromol/g). GLUT-4 protein in fast-twitch white muscle followed a pattern similar to fast-twitch red muscle. These results indicate that carbohydrate supplementation, provided with exercise, will enhance GLUT-4 protein expression by increasing translational efficiency. Conversely, postexercise fasting appears to upregulate GLUT-4 mRNA, possibly to amplify GLUT-4 protein expression on an increase in glucose availability. These regulatory mechanisms may help control muscle glucose uptake in accordance with glucose availability and protect against postexercise hypoglycemia.     

Effect of duration and exogenous carbohydrate on gross efficiency during cycling

The purpose of this investigation was to determine the effects of 2.5 hours of cycling with and without carbohydrate supplementation on gross efficiency (GE). Trained cyclists (N = 15) were tested for V(.-)O2max (53.6 + 2.2 ml x kg(-1) x min(-1)) and lactate threshold during incremental tests to exhaustion. On 2 separate visits, cyclists performed 2.5 hours of cycling on an indoor trainer. A carbohydrate (C) or placebo (P) beverage was randomly provided and counterbalanced for each of the trials. Gross efficiency, cycling economy, power output, V(.-)O2, lactate, and blood glucose were measured every 20 minutes during the 2.5-hour ride. Muscle glycogen was measured immediately before and after the ride from the vastus lateralis. Results indicated that power output and V(.-)O2 decreased over time (p < 0.05) but were not different between trials. Relative GE and cycling economy during C were greater than P at 40 and 150 minutes (p < 0.05). Blood glucose significantly decreased in P and was lower than C at all time points (p < 0.05). Respiratory exchange ratio decreased over time in both trials, with a significant treatment effect at 40 and 150 minutes (p < 0.05). Muscle glycogen decreased by 65% during both conditions (p < 0.05) but demonstrated no treatment effect. We conclude that carbohydrate supplementation during 2.5 hours of cycling attenuated the decrease in GE possibly by maintaining blood glucose levels. This suggests that the positive effect of carbohydrate supplementation on endurance performance may be through the maintenance of metabolic efficiency.     

STUDIES ON CELL METABOLISM AND CELL DIVISION : VI. OBSERVATIONS ON THE GLYCOGEN CONTENT,CARBOHYDRATE CONSUMPTION,LACTIC ACID PRODUCTION,AND AMMONIA PRODUCTION OF EGGS OF ARBACIA PUNCTULATA

1. Under the present conditions of experiment, Arbacia eggs were found to contain an average of 110 mg. of acid-hydrolyzable carbohydrate (calculated as glucose) per gm. of egg protein. This carbohydrate was almost all in the egg proper, little or none being found in the jelly. To permit conversion of the data to other bases of reference the relation of nitrogen content to wet and dry weight and to egg number were determined. The eggs were found to contain 23.9 per cent solids, 0.10 mg. nitrogen per mg. dry weight, and 5.93 mg. nitrogen per 10⁶ cells. From these results, about 7 per cent of the egg dry weight is acid-hydrolyzable carbohydrate and about 65 per cent is protein. 2. Approximately one-half of the total acid-hydrolyzable carbohydrate was isolated in the form of an alkali-stable, alcohol-precipitable carbohydrate. This substance gave a typical glycogen color test with iodine, yielded glucose on acid hydrolysis, and had, within the limits of experimental error, the same optical rotation as glycogen from other animal sources. Since known amounts of glycogen were completely recovered when carried through the isolation process, the nature of one-half of the acid-hydrolyzable carbohydrate of Arbacia eggs remains undetermined. 3. In order to gain some estimate of the extent to which Arbacia eggs utilize their total carbohydrate for development, determinations of the oxygen consumption, respiratory quotient, carbohydrate consumption, lactic acid production, and ammonia production were made. While all samples of eggs were found to utilize carbohydrate from the 15th to the 24th hours of development at 20°C., certain samples of eggs consumed little or no carbohydrate from the 1st to the 6th hours, the period during which cell division proceeds most rapidly. In a number of instances where carbohydrate breakdown was lacking, a substantial proportion of the oxygen consumption could be accounted for on the basis of processes involving oxidation of protein or protein breakdown products.     

Anaerobiosis in the nematode Caenorhabditis elegans

In Caenorhabditis elegans, mortality rates and changes in concentrations of carbohydrate stores and anaerobic end products were determined in anoxic (test) and normoxic (control) animals at two different temperatures (10 and 20 degrees C). The anoxic tolerance of the free-living nematode proved to be well-developed: at 10 degrees C, about 50% of animals had survived a period of 50 h of anoxia. The carbohydrate stores (approximately 30 mmol glycosyl units kg-1 freshweight (FW)) were reduced by two-thirds within 24 h of anoxia at both temperatures. L-lactate, acetate, succinate, and propionate were identified as the main anaerobic end products. The amounts and proportions of the end products were dependent on temperature. They did not accumulate very much in the tissues, but were mainly excreted. During anoxia, the metabolism of C. elegans was depressed to 3-4% of the aerobic value. The food-source Escherichia coli was found to be at least partly alive in the gut of the animals. To separate between anaerobiosis in animals and bacteria, cleaning procedures were applied, and additional control measurements were made: anaerobic end products produced either by E. coli alone or by bacteria-free (axenic) bred nematodes were quantified at identical incubation conditions.     

Investigations of the anaerobic metabolism of the polychaete wormNereis diversicolor M.

Summary The anaerobic metabolism ofNereis diversicolor M. was studied during various periods of experimental anaerobiosis.The degradation of glycogen is shown to be the main source of anaerobic energy production. During first hours of anaerobiosis, aspartate, in addition to glycogen, is metabolized in considerable quantities.Five acids were found to accumulate as end-products: alanine, D-lactate, succinate, acetate and propionate (Table 2).Alanine is accumulated only during the first hours of anaerobiosis. The increase in alanine is correlated with a decrease in aspartate.D-Lactate is the main end-product during the first 24 h of anaerobiosis, and continues to be produced even during prolonged anaerobiosis. In accordance with lactate production,Nereis diversicolor possesses a high glycolytic capacity (Table 4).The major end-products of long term fermentation are propionate and acetate. In contrast to other end-products, these acids are excreted in substantial amounts.Abbreviations GAPDH glyceraldehydephosphate dehydrogenase, EC 1.2.1.12 - LDH lactate dehydrogenase, EC 1.1.1.27 - GOT aspartate aminotransferase, EC 2.6.1.1 - GPT alanine aminotransferase, EC 2.6.1.2 - MDH malate dehydrogenase, EC 1.1.1.37 Supported by Deutsche Forschungsgemeinschaft (Gr 456/5 and Gr 456/6)     

Partial restoration of dietary fat induced metabolic adaptations to training by 7 days of carbohydrate diet.

We tested the hypothesis that a shift to carbohydrate diet after prolonged adaptation to fat diet would lead to decreased glucose uptake and impaired muscle glycogen breakdown during exercise compared with ingestion of a carbohydrate diet all along. We studied 13 untrained men; 7 consumed a high-fat (Fat-CHO; 62% fat, 21% carbohydrate) and 6 a high-carbohydrate diet (CHO; 20% fat, 65% carbohydrate) for 7 wk, and thereafter both groups consumed the carbohydrate diet for an eighth week. Training was performed throughout. After 8 wk, during 60 min of exercise (71 +/- 1% pretraining maximal oxygen uptake) average leg glucose uptake (1.00 +/- 0.07 vs. 1.55 +/- 0.21 mmol/min) was lower (P < 0.05) in Fat-CHO than in CHO. The rate of muscle glycogen breakdown was similar (4.4 +/- 0.5 vs. 4.2 +/- 0.7 mmol. min(-1). kg dry wt(-1)) despite a significantly higher preexercise glycogen concentration (872 +/- 59 vs. 688 +/- 43 mmol/kg dry wt) in Fat-CHO than in CHO. In conclusion, shift to carbohydrate diet after prolonged adaptation to fat diet and training causes increased resting muscle glycogen levels but impaired leg glucose uptake and similar muscle glycogen breakdown, despite higher resting levels, compared with when the carbohydrate diet is consumed throughout training.     

The energy production of juvenileArenicola marina (Polychaeta) under anoxic and hypoxic conditions

The mode of anaerobic energy production of juvenileArenicola marina (0-generation) was investigated under experimental conditions and in the biotope. Under experimental anaerobic conditions, juvenileA. marina produce energy by the pathways known from the adults and other euryoxic invertebrates with succinate and the volatile fatty acids, acetate and propionate, as main end products. However, the juvenile lugworms are less resistent to anoxia than the adults. The reasons for this might be their small glycogen stores and their limited ability to reduce the metabolic rate. Nevertheless, on the tidal flats the juveniles settle particularly in the area next to the high tide line, which offers such extreme conditions that adult lugworms cannot live there. This different behaviour can be explained by the dissimilar ability to use oxygen at very low partial pressures. Juveniles maintain an aerobic energy metabolism even at a P_{WO 2} of 15 Torr at which adults are forced to produce energy exclusively by the less effective anaerobic mode. In the field, no indications of an anaerobic energy metabolism were detected in juveniles even after an exposure of 8 hours.     

Stoichiometric model of the aerobic metabolism of the biological phosphorus removal process

In the aerobic phase of the biological phosphorus removal process, poly-beta-hydroxybutyrate, produced during anaerobic conditions, is used for cell growth, phosphate uptake, and glycogen formation. A metabolic model of this process has been developed. The yields for growth, polyphosphate and glycogen formation are quantified using the coupling of all these conversions to the oxygen consumption. The uptake of phosphate and storage as polyphosphate is shown to have a direct effect on the observed oxygen consumption in the aerobic phase. The overall energy requirements for the P-metabolism are substantial: 25% of the acetate consumed during anaerobic conditions and 60% of the oxygen consumptions is used for the synthesis of polyphosphate and glycogen. (c) 1994 John Wiley & Sons, Inc.     

Metabolic reserves associated with pupal diapause in the flesh fly, Sarcophaga crassipalpis

Larvae of Sarcophaga crassipalpis destined for pupal diapause (light:dark 12:12, 20°C) contain nearly twice as much lipid and twice the haemolymph protein concentration as larvae that will not enter diapause (light:dark 15:9, 20°C). This conspicuous difference in metabolic reserves provides the earliest indication of the developmental fate of the larva. Lipid reserves are utilized rapidly during the first half of diapause and then remain stable until adult eclosion. In contrast, residual dry weight changes very little early in diapause but drops sharply late in diapause, thus implying a transition from lipid utilization to protein or carbohydrate utilization in mid-diapause. We suggest that this metabolic transition marks the end of the “fixed latency period”: pupae readily respond to environmental or hormonal stimulation after this point. Diapause-destined larvae did not accumulate more glycogen than nondiapause-destined larvae, but an 80% decrease in glycogen at the onset of diapause and its elevation at the end of diapause suggests the utilization of glycerol or related compounds as cryoprotectants during diapause. Profiles of water content are very similar in short-day and long-day flies, thus suggesting that dehydration is not a mechanism exploited by the flesh fly to achieve cold hardiness. Adult flies that have experienced pupal diapause emerge from the puparium with lipid, glycogen, and water content nearly identical to flies that have not experienced diapause, but the residual dry weight is much lower. The severe depletion of protein may account for the reduced fecundity of flies that have experienced diapause.     

Energy Metabolism and Survival of the Infective Juveniles of Steinernema carpocapsae under Oxygen-Deficient Conditions

Energy metabolism and its relation to survival of the infective juveniles (IJ) of S. carpocapsae under anaerobic and oxygen-deficient conditions were studied by monitoring changes in survival rate, levels of key energy reserve materials, oxygen consumption, and respiratory quotient (RQ). The effects of various factors on the survival of IJ under anaerobic conditions were also investigated. Under anaerobic conditions, the IJ were inactivated but could survive for several days in an immobile state, using the carbohydrate reserves glycogen and trehalose for energy supply. The survival time of IJ was mainly dependent on the availability of energy supply, which, in turn, was influenced by factors such as temperature and metabolic by-products. Surviving, anaerobically incubated IJ fully recovered upon return to aerobic conditions. Recovering IJ were characterized by regaining mobility and restoration of carbohydrate reserves consumed during the anaerobic period. Carbohydrate reserves were restored by conversion from lipid reserves and possibly from anaerobic metabolic by-products. The infectivity of IJ recovered from the anaerobic state was not affected. At 1% oxygen level, IJ were also immobile and mainly depended on carbohydrate reserves for energy supply and the RQ was greater than 1. However, some oxygen was consumed; the survival time of these IJ was shorter than those kept in natural air but longer than those under anaerobic conditions. When IJ were incubated at oxygen levels of 3% to 21%, the RQs were maintained at 0.7 to 0.8. Oxygen consumption rates and the reduction in both mean dry weight and lipid levels were proportional to oxygen levels while the survival time of IJ was inversely proportional to oxygen levels.     

Carbohydrate catabolism in the plerocercoids of Schistocephalus solidus (Cestoda: Pseudophyllidea)

The plerocercoids of S. solidus possess a complete sequence of glycolytic and tricarboxylic acid cycle enzymes. The presence of phosphoenolpyruvate carboxykinase and fumarate reductase activity and the relatively low activities of aconitase and isocitrate dehydrogenase suggest that carbon dioxide fixation is an important pathway in this parasite. Carbon balances show that glycogen is the main energy source under both aerobic and anaerobic conditions and there is only a slight Pasteur effect. Aerobically 22·5% of the glycogen catabolized is excreted as acetate and propionate (4:1), anaerobically 70% of the glycogen utilized can be accounted for as acetate and propionate (1:3). The results indicate that anaerobically the plerocercoids fix carbon dioxide and have a partial reversed tricarboxylic acid cycle, whilst under aerobic conditions at least part of the carbohydrate may be oxidized via a functional tricarboxylic acid cycle.     

Ingestion of a high-glycemic index meal increases muscle glycogen storage at rest but augments its utilization during subsequent exercise.

The aim of this study was to compare the effect of preexercise breakfast containing high- and low-glycemic index (GI) carbohydrate (CHO) (2.5g CHO/kg body mass) on muscle glycogen metabolism. On two occasions, 14 days apart, seven trained men ran at 71% maximal oxygen uptake for 30 min on a treadmill. Three hours before exercise, in a randomized order, subjects consumed either isoenergetic high- (HGI) or low-GI (LGI) CHO breakfasts that provided (per 70 kg body mass) 3.43 MJ energy, 175 g CHO, 21 g protein, and 4 g fat. The incremental areas under the 3-h plasma glucose and serum insulin response curves after the HGI meal were 3.9- (P < 0.05) and 1.4-fold greater (P < 0.001), respectively, than those after the LGI meal. During the 3-h postprandial period, muscle glycogen concentration increased by 15% (P < 0.05) after the HGI meal but remained unchanged after the LGI meal. Muscle glycogen utilization during exercise was greater in the HGI (129.1 +/- 16.1 mmol/kg dry mass) compared with the LGI (87.9 +/- 15.1 mmol/kg dry mass; P < 0.01) trial. Although the LGI meal contributed less CHO to muscle glycogen synthesis in the 3-h postprandial period compared with the HGI meal, a sparing of muscle glycogen utilization during subsequent exercise was observed in the LGI trial, most likely as a result of better maintained fat oxidation.     

Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion

The time of ingestion of a carbohydrate supplement on muscle glycogen storage postexercise was examined. Twelve male cyclists exercised continuously for 70 min on a cycle ergometer at 68% VO2max, interrupted by six 2-min intervals at 88% VO2max, on two separate occasions. A 25% carbohydrate solution (2 g/kg body wt) was ingested immediately postexercise (P-EX) or 2 h postexercise (2P-EX). Muscle biopsies were taken from the vastus lateralis at 0, 2, and 4 h postexercise. Blood samples were obtained from an antecubital vein before and during exercise and at specific times after exercise. Muscle glycogen immediately postexercise was not significantly different for the P-EX and 2P-EX treatments. During the first 2 h postexercise, the rate of muscle glycogen storage was 7.7 mumol.g wet wt-1.h-1 for the P-EX treatment, but only 2.5 mumol.g wet wt-1.h-1 for the 2P-EX treatment. During the second 2 h of recovery, the rate of glycogen storage slowed to 4.3 mumol.g wet wt-1.h-1 during treatment P-EX but increased to 4.1 mumol.g wet wt-1.h-1 during treatment 2P-EX. This rate, however, was still 45% slower (P less than 0.05) than that for the P-EX treatment during the first 2 h of recovery. This slower rate of glycogen storage occurred despite significantly elevated plasma glucose and insulin levels. The results suggest that delaying the ingestion of a carbohydrate supplement post-exercise will result in a reduced rate of muscle glycogen storage.     

STUDIES OF NATIVE GLYCOGEN ISOLATED FROM SYNCHRONIZED TETRAHYMENA PYRIFORMIS (HSM)

Native glycogen was isolated from Tetrahymena pyriformis (HSM) by isopycnic centrifugation in cesium chloride density gradients. A density of 1.62 to 1.65 was isopycnic for glycogen. Most of the banded glycogen existed as 35 to 40 mµ particles which had a sedimentation coefficient of 214. These particles were composed of aggregates of 2 to 3 mµ spherical particles. Extraction of glycogen with hot alkali reduced the sedimentation coefficient of native glycogen from 214 to 64.7 and the particle diameter from approximately 40 to 20 mµ and smaller. Cell division was synchronized by a repetitive 12-hour temperature cycle, and glycogen was measured at several times during the cell cycle. The temperature cycle consisted of 9.5 hours at 12°C and 2.5 hours at 27°C. Approximately 90 per cent of the cells divided during the last 1.5 hours of the warm period. The carbohydrate/protein ratio of cells at the end of the cold period was 0.27 and was reduced slightly during the warm period. Glucose was incorporated into glycogen during both periods, although the rate of incorporation was greater during the warm period. No preferential incorporation on the basis of particle size was noted. Incorporation was measured in both native glycogen and KOH-extracted glycogen. Tetrahymena glycogen is compared with rat liver glycogen previously isolated by similar procedures, and the significance of using combined rate-zonal and isopycnic centrifugation for isolating native glycogen is discussed.     

Anaerobic and aerobic energy metabolism in the larvae (tetrathyridia) of Mesocestoides corti

The tetrathyridia of Mesocestoides corti produce lactate, succinate, acetate, and CO₂ as major carbon-containing end products during in vitro incubation with glucose as the substrate. Differences in the rate of glucose consumption and lactate production under anaerobic or aerobic conditions were observed, but their significance could not be determined. However, succinate production was greatly decreased in the presence of oxygen.The relative activities and intracellular distribution of various enzymes involved in energy-supplying metabolism of the larvae appear to conform to the pathways observed in other parasitic helminths known to produce lactate, succinate, and volatile fatty acids as metabolic end products. Some common features found in this respect are the relatively low pyruvate kinase activity, the presence of a highly active cytoplasmic phosphoenolpyruvate carboxylase and the capability of mitochondrial membrane bound fumarate reductase to reduce fumarate by means of NADH. Although a stimulatory effect of fructose-1,6-diphosphate on the reaction velocity of pyruvate kinase occurred, the absolute activity of this enzyme is very low.Nearly all the enzymes required for Krebs cycle activity are available in the tetrathyridia. Under the assay conditions employed by us, only NAD-dependent isocitrate dehydrogenase could not be demonstrated. The small amounts of ¹⁴CO₂ liberated from 6-¹⁴C-glucose suggest that the cycle in its classical form probably only functions at a very low rate. The incorporation of ¹⁴C from labeled glucose into glycogen indicates the presence of enzymes capable of glycogenesis. The incorporation rate was found to be higher in the presence of oxygen than under anaerobic conditions. On account of the very low NAD-linked glycerol-3-phosphate dehydrogenase activity the glycerolphosphate cycle may be of minor importance for the tetrathyridia.As a result of these studies a scheme for the main carbohydrate dissimilating pathways in the tetrathyridia is proposed and the significance of oxygen with respect to energy-supplying metabolism is discussed.     

Metabolic model for glycogen-accumulating organisms in anaerobic/aerobic activated sludge systems

Glycogen-accumulating organisms (GAO) have the potential to directly compete with polyphosphate-accumulating organisms (PAO) in EBPR systems as both are able to take up VFA anaerobically and grow on the intracellular storage products aerobically. Under anaerobic conditions GAO hydrolyse glycogen to gain energy and reducing equivalents to take up VFA and to synthesise polyhydroxyalkanoate (PHA). In the subsequent aerobic stage, PHA is being oxidised to gain energy for glycogen replenishment (from PHA) and for cell growth. This article describes a complete anaerobic and aerobic model for GAO based on the understanding of their metabolic pathways. The anaerobic model has been developed and reported previously, while the aerobic metabolic model was developed in this study. It is based on the assumption that acetyl-CoA and propionyl-CoA go through the catabolic and anabolic processes independently. Experimental validation shows that the integrated model can predict the anaerobic and aerobic results very well. It was found in this study that at pH 7 the maximum acetate uptake rate of GAO was slower than that reported for PAO in the anaerobic stage. On the other hand, the net biomass production per C-mol acetate added is about 9% higher for GAO than for PAO. This would indicate that PAO and GAO each have certain competitive advantages during different parts of the anaerobic/aerobic process cycle.     

Anaerobic incorporation of radioactivity from 2,3-14C-succinic acid into citric acid cycle intermediates and related compounds in the sea musselMytilus edulis L.

Summary Sea mussels were exposed to nitrogen for various periods (0, 1, 3 and 6 days) and subsequently injected with 2,3-¹⁴C-succinic acid. After 2.5 h anaerobic incubation concentrations of succinate, some amino acids and volatile fatty acids were determined as well as the distribution of radioactivity.Conversion of the precursor decreased from 80 to 40%, due to increased dilution with endogenous succinate, accumulated during the anaerobic preincubation period.More than 80% of the activity of the converted 2,3-¹⁴C-succinic acid was incorporated into malate, aspartate, glutamate, alanine and propionate. This indicates that succinate is not only an end product of anaerobic glycogen breakdown, but remains an active intermediate of the tricarboxylic acid cycle, which can still operate under anaerobic conditions.Concentration and radioactivity of propionate were markedly increased after prolonged anoxia, which gives evidence that succinate is actively converted to propionate during anaerobiosis.Observed accumulation of glutamate during anoxia is explained by incomplete oxidation of pyruvate, which leaves the tricarboxylic acid cycle at the stage of 2-ketoglutarate.