Pathways Of Glucose Utilization Research Articles

13C and 31P NMR studies on sugar metabolism in Bombyx mori and Philosamia cynthia ricini larvae

Studies were made on 13C and 31P NMR in larvae of two species of silkworm, Bombyx mori and Philosamia cynthia ricini, in vivo as well as in vitro to determine the pathways of glucose utilization, especially those to amino acids as components of silk fibroin. Results showed that the 13C of [1- 13C]glucose administered orally into 5th instar larvae of both species was incorporated into glucose-1-phosphate, glucose-6-phosphate and trehalose. Serine, glutamate, glutamine, citrate, malate, trehalose and sorbitol-6-phosphate were detected in the hemolymphs of these larvae as metabolites of [1- 13C]glucose. Two days after [1- 13C]glucose administration, labeled alanine, glycine, serine, urea, glycogen, trehalose and glycerol were clearly detected in Bombyx larvae. Starvation caused rapid consumption of administered [1- 13C]glucose with very little accumulation of 13C in glycogen or trehalose. In the in vivo 31P NMR spectra of Bombyx larvae, ATP, arginine phosphate, sorbitol-6-phosphate, uridine diphosphoglucose, phosphoenolpyruvate and inorganic phosphate were detected with some sugar phosphates, such as glucose-1-phosphate and glucose-6-phosphate. During starvation, the intensity of the signal of inorganic phosphate increased and those of sugar phosphate other than sorbitol-6-phosphate decreased, but these changes were reversed by oral administration of glucose.

Alternative pathways of glucose utilization in developing rat spinal cord

The activities of alternative pathways of glucose utilization in the developing rat spinal cord were evaluated from the release of (14)CO(2) and the incorporation of [(14)C] into lipids from differentially labelled glucose. Total lipid synthesis had peak activity at 15 days post-partum corresponding to the period of peak myelination in rat spinal cord. The activities of the glycolytic route, tricarboxylic acid cycle and fully activated pentose phosphate pathway were highest up to 20 days post-partum. After this period myelin (which is biochemically relatively inert) will constitute a larger proportion of the mass of the cord and this may contribute to the lower observed rates of the above pathways during later stages of development. Treatment of 20 day old rats with 6-aminonicotinamide resulted in spastic paralysis of the rats and pronounced inhibition of the pentose phosphate pathway indicating that this pathway, although low in activity (less than 4% of total glucose oxidation) has an important role in developing rat spinal cord.

Pyridine nucleotide analog interference with metabolic processes in mitogen-stimulated human T lymphocytes

The differential metabolic effects of three nicotinamide analogs, 6-aminonicotinamide, 3-aminobenzamide, and 5-methylnicotinamide, were analyzed in mitogen-stimulated preparations of human T lymphocytes. Mitogen stimulation with the phorbol ester TPA and a monoclonal antibody to the T3 cell surface antigen caused an increase in cellular NAD and ATP levels and a marked increase in glucose metabolism as demonstrated by an increase in cellular levels of glucose 6-phosphate and a sevenfold increase in radioactive CO 2 formation from [1- 14C]glucose. 6-Aminonicotinamide had drastic inhibitory effects on the mitogen-stimulated increases in NAD and ATP levels as well as on the metabolism of glucose. Treatment of the mitogen-stimulated cells with 6-aminonicotinamide also caused a marked increase in cellular levels of 6-phosphogluconate, suggesting inhibition of the hexose monophosphate shunt at 6-phosphogluconate dehydrogenase. Radioactive CO 2 formation from [6- 14C]glucose showed that metabolism through the tricarboxylic acid cycle was not used to compensate for the inhibition of the hexose monophosphate shunt pathway. Treatment of cells with 3-aminobenzamide had the opposite effect of 6-aminonicotinamide in that cellular NAD levels increased, presumably due to inhibition of poly(ADP-ribose) polymerase. 3-Aminobenzamide did not interfere with ATP or glucose 6-phosphate levels and did not cause significant elevations of 6-phosphogluconate. Thus, 6-aminonicotinamide appears to have direct inhibitory effects on the synthesis of both pyridine nucleotides and poly(ADP-ribose), whereas 3-aminobenzamide has its major inhibitory effect on poly(ADP-ribose) synthesis. 5-Methylnicotinamide also interferes with the mitogen-stimulated increase in NAD levels but not as effectively as 6-aminonicotinamide. The alterations in pyridine nucleotide metabolism resulting from treatment with these nicotinamide analogs can produce drastic and diverse alterations in pathways of glucose utilization and energy generation.

Glycoconjugates as noninvasive probes of intrahepatic metabolism: pathways of glucose entry into compartmentalized hepatic UDP-glucose pools during glycogen accumulation.

Recent studies have questioned the efficiency with which administered glucose generates hepatic glycogen through the direct nonrecycling route compared with the indirect route from glucose recycled through glycolysis followed by gluconeogenesis. Using fasted and refed rats, we examined the relative access of infused [1-3H]- and [U-14C]glucose by way of these two pathways to liver glycogen and to hepatic glucuronic acid, the latter recovered from the urine as the glucuronide conjugated with administered acetaminophen. In fasted animals and during early refeeding, extensive dilution of administered [3H]- and [14C]glucose recovered in glycogen showed that 60-70% of the labeled glucose had undergone recycling by the indirect route. As refeeding progressed with substantial glycogen deposition, the contribution of the recycling pathway to glycogen and glucuronic acid diminished considerably. Thus, there is a shift in pathways of hepatic glucose utilization as liver glycogen accumulates. Consequently, the ratio of 3H/14C in glucuronic acid was closely correlated with the glycogen content of the liver at sacrifice, indicating that this ratio may prove useful as a noninvasive indicator of liver glycogen concentration. Since glycogen and glucuronic acid are derived by single reactions from UDP-glucose, they should show a common labeling pattern with 3H and 14C under various nutritional conditions. However, detailed analysis of their labeling patterns showed a striking divergence, implying that there must be compartmentation of the UDP-glucose pools leading to each of these end products, either because they are made in separate compartments within the same cell or because each is made in different hepatocyte populations. We favor the former explanation because galactose secreted in glycoproteins shows 3H and 14C labeling patterns similar to those of glucuronic acid conjugated with acetaminophen, and both of these conjugations occur in the endoplasmic reticulum of the liver, whereas most glycogen is present in the cytosol.

Equations and calculations of product yields and preferred pathways for butanediol and mixed‐acid fermentations

Using the available information of fermentation biochemistry, fermentation (stoichiometric) equations are derived for anaerobic saccharolytic fermentations of butanediol and mixed acids. The equations describe the interrelations among the fermentation products, biomass, and consumed substrate (glucose). The validity of the equations is tested using a variety of batch data from the literature. The validity of the equations is expected to extend to steady-state and transient fermentations, as well. Uses, improvements, and extensions of the equations are also discussed in detail. Among others, it is shown that the equations are useful for checking the consistency of experimental data, for calculating maximal yields and selectivities for the fermentation products, and calculating the extent of utilization of the Embden-Meyerhof-Parnas pathway versus the Hexose Monophosphate pathway of glucose utilization.

Oxytocin: Anti-insulin-like effects in isolated fat cells

Oxytocin has both insulin-like and insulin antagonistic actions in fat cells in vitro. The anti-insulin-like effects of oxytocin in dispersed rat fat cells have been studied. The magnitude of the anti-insulin-like activity varies with the metabolic pathway of glucose utilization; oxidation [ 14CO 2 production], 32%; glycogen synthesis ( d-[U- 14C] glucose incorporation into glycogen), 77%. In addition, direct inhibition of the activation of fat cell glycogen synthase has been shown. These inhibitory effects depend upon an intact disulfide ring, since the ability of N-ethylmaleimide-reacted oxytocin to inhibit insulin-stimulated processes was reduced by more than 90% when compared to the intact molecule.

Alternative pathways of glucose utilization in brain: changes in the pattern of glucose utilization and of the response of the pentose phosphate pathway to 5-hydroxytryptamine during aging.

The oxidation of differentially labelled glucose, pyruvate and glutamate in brain slices from rats aged 20 days to 26 months has been studied and the partition of the glucose used into the glycolytic-tricarboxylic acid cycle pathway, the pentose phosphate pathway and the glutamate-GABA shunt has been calculated. Over the time range 4 to 26 months, there is an approximately 20% decrease in the production of CO2 via the glycolytic-tricarboxylic acid cycle route, as there is in the rate of glucose phosphorylation. The glutamate-GABA pathway falls by about 50% over this same time span. The broad activity of the pentose phosphate pathway falls rapidly and cannot be detected in the brains of rats aged 18 months or more, whereas the fully stimulated pathway, i.e. in the presence of the artificial electron acceptor phenazine methosulphate, declines only marginally over this period, falling sharply only after 23 months. The pentose phosphate pathway is stimulated by the presence of 5-hydroxytryptamine and this stimulation appears to increase with age.

Alternative pathways of glucose utilization in brain; changes in the pattern of glucose utilization in brain resulting from treatment of rats with 6-aminonicotinamide.

The effect of 6-aminonicotinamide (6AN) treatment on the activities of alternative pathways of glucose metabolism in 20-day-old rat brain was evaluated by measurements of yields of 14CO2 from glucose labeled with 14C on carbons 1, 2, 3 + 4, or 6 and uniformly labeled glucose, and from the incorporation of 14C from specifically labeled glucose into lipids by brain slices from cerebral hemispheres and cerebellum. At the highest dose of 6AN used (35 mg/kg body weight) there was a significant decrease in the 14CO2 yields via the pentose phosphate pathway, the glycolytic route, tricarboxylic acid (TCA) cycle, and via the glutamate-gamma-aminobutyric acid pathway. Giving a graded series of doses (20-35 mg 6AN/kg body weight) revealed a hierarchy of responses in which the pentose phosphate pathway, lactate, glyceride-glycerol, and fatty acid formation were most sensitive, followed, in sequence, by the pyruvate dehydrogenase reaction, the glutamate-gamma-aminobutyrate route and, finally, the TCA cycle. The nature of the blocks in the various pathways was examined by the use of metabolite profiles.

Alternative pathways of glucose utilization in brain. Changes in the pattern of glucose utilization in brain during development and the effect of phenazine methosulfate on the integration of metabolic routes

The activities of alternative pathways of glucose metabolism in developing rat brain were evaluated by measurement of the yields of 14CO 2 from glucose labeled with 14C on carbons 1, 2, 3 + 4, 6 and uniformly labeled glucose, from the detritiation of [2- 3H]glucose and from the incorporation of 14C from specifically labeled glucose into lipids by brain slices from cerebral hemispheres and cerebellum. The glycolytic route and tricarboxylic acid cycle ( 14CO 2 yield from carbons 3, 4, and 6 of glucose) increased during development. The flux through the glutamate-γ-aminobutyric route ( 14CO 2 yield from carbon 2-carbon 6 of glucose) also showed an increase with development. In contrast, the proportion of glucose metabolized via the pentose phosphate pathway was markedly decreased as development progressed. The artificial electron acceptor, phenazine methosulfate, was used as a probe to investigate the effect of alterations in the redox state of NADP + NADPH couple on a number of NADP-linked systems in developing brain. Phenazine methosulfate produced a massive (20- to 50-fold) stimulation of the pentose phosphate pathway, in contrast, the incorporation of glucose carbon into fatty acids and flux through the glutamate-γ-aminobutyrate shunt were sharply decreased. The effects of phenazine methosulfate on the incorporation of glucose into glyceride glycerol, on the flux of glucose through the pyruvate dehydrogenase reaction and tricarboxylic acid cycle, all processes linked to the NAD + NADH couple, appeared to be minimal in the brain at the stages of development studied, i.e., 1, 5, 10, 20 days, and in the adult rat. The significance of the massive reserve potential of the pentose phosphate pathway in the developing brain is discussed.

Effects of dietary composition on adipose tissue hexokinase-II and glucose utilization in normal and streptozotocin-diabetic rats.

The control of adipose tissue hexokinase isoenzymes in response to altered dietary composition was investigated. Rats that were fasted and then refed carbohydrate-free diets increased their HK-II activity in epididymal fat pads above the level in fasted animals. However the ultimate activity of HK-II achieved during refeeding with seven diets of varying composition was dependent mainly on dietary carbohydrate; the effect of dietary carbohydrate overcame poor growth due to protein deficiency or decreased food intake. Fat pads from animals fed for three weeks from weaning with 19 per cent protein diets showed a marked increase in HK-II on 51 per cent carbohydrate over those on a carbohydrate-free diet but no further increase on 81 per cent carbohydrate. However, adipocytes from rats on 81 per cent carbohydrate had significantly higher HK-II than those from rats on 51 per cent carbohydrate. In streptozotocin-diabetic rats there was no difference in adipose tissue HK-II between rats on 19 per cent protein-51 per cent carbohydrate and those on 19 per cent protein carbohydrate-free diets. Treatment of diabetic rats with 3 U. lente insulin daily brought HK-II into the range for normal rats, but once again there was no difference between the two diets. The treated rats showed marked weight gain but were still hyperglycemie. Adipocytes from rats on the 19 per cent protein carbohydrate-free diet showed lower HK-II and glucose conversion to CO2 and triglyceride than adipocytes from rats on the 51 per cent carbohydrate diet. There was a high correlation of HK-II to both pathways of glucose utilization on both diets. However, the slope of the regression line of triglyceride production on HK-II was much lower on the carbohydrate-free than on the basal diet. Adipocytes from rats on the 81 per cent carbohydrate diet had HK-II activity and glucose utilization that fell within the 95 per cent confidence limits for the relationship derived from adipocytes from rats on the 51 per cent carbohydrate diet. Values for glucose utilization in adipocytes from treated diabetic rats on the carbohydrate-free diet were above the expected range for this diet for both CO2 and triglyceride production; CO2 production was also above the expected range for diet in treated diabetic rats on the 51 per cent carbohydrate diet. Glucose conversion to both end products was higher for a given level of HK-II in the treated diabetic animals on the 51 per cent carbohydrate diet than on the carbohydrate-free diet. These data indicate that diet has a major effect on HK-II that is probably mediated by carbohydrate and is dependent on insulin. Although there appears to be a relationship between HK-H and glucose utilization in a given diet-and-treatment group, there is a departure from the normal relationship in adipocytes from rats on a high-fat carbohydrate-free diet or from partially treated diabetic rats.

The potential use of inhibitors of glycerol-3-phosphate oxidase for chemotherapy of African trypanosomiasis

The bloodstream forms of African trypanosomes, responsible for sleeping sickness in man, are completely dependent on glycolysis for their energy supply, because the biogenesis of a mitochondrial respiratory chain is suppressed in the vertebrate host [l-4] . The present ideas on trypanosome glycolysis are presented in a simplified form in fig.1. Grant and Fulton [5] showed that the flow of carbon is consistent with the view that the Embden-Meyerhof scheme is the only pathway of glucose utilization. Pyruvate is not further metabolized because of the absence of a functional Krebs cycle [6,7] and the lack of lactate dehydrogenase [8] and is excreted into the host blood. The NAD’ reduced in the glyceraldehyde phosphate dehydrogenase step is reoxidized by a Lglycerol-3-phosphate oxidase system [9] , unique to trypanosomes (boxed in fig. 1). According to fig. 1 this oxidase system is essential for survival of bloodstream trypanosomes. Since it is absent in the mammalian host, it should provide an ideal target for a selective chemotherapeutic agent. This paper deals with the effect of salicylhydroxamic acid (SHAM), a powerful inhibitor of the glycerolphosphate oxidase system in trypanosomes, on glycolysis and on the energy production of isolated, intact trypanosomes. Although the oxidase is completely blocked by 1 mM SHAM, we have found that motility and ATP production are not drastically

Effects of medroxy-progesterone acetate on rat fat cell metabolism.

The effects of medroxyprogesterone acetate (MPA) on rat fat cell metabolism were investigated. 8 female rats received 10 mg MPA/kg (Depo-Provera) im and 8 served as controls for 4 weeks. 3-5 days after the last injection parametrial fat was excised and fat cells from each rat were isolated for fat determination or for the measurement of radioactivity in corporated into carbon dioxide and triglycerides. The results showed that glucose oxidation to carbon dioxide as well as incorporation into total lipids was significantly lower (p less than .001) in fat cells of MPA-treated rats when expressed on the basis of fat content. The differences between the 2 groups were marked only when glucose-1-carbon-14 served as substrate. However there appeared to be no qualitative difference in the metabolic pathways of glucose utilization of treated and control rats. The mean cell fat:protein ratio was 336 and 194 in the MPA and control groups respectively. The results suggest that MPA caused cellular enlargement due to increased fat deposition and a corresponding decrease in glucose utilization. This study underscores the differences one may encounter when data are expressed in terms of fat content vs. protein content of fat cells.

Different pathways for fructose and glucose utilization in Rhodopseudomonas capsulata and demonstration of 1-phosphofructokinase in phototrophic bacteria

Rhodopseudomonas capsulata Kb1 utilizes glucose via the Entner—Doudoroff pathway and fructose via the Embden—Meyerhof pathway. In this bacterium, 1-phosphofructokinase (EC 2.7.1.56) is the key enzyme of the Embden—Meyerhof pathway and is induced by fructose but not by glucose. This enzyme could also be demonstrated in various species of phototrophic bacteria after growth in fructose-salts medium.

Physical Characteristics and Chemi-osmotic Transformations of Mutarotases from Various Species

Abstract Previous studies indicated that the function of mutarotase (aldose-1-epimerase) in glucose metabolism in primitive organisms should have become redundant with the evolution of the phosphorylitic pathways of glucose utilization and suggested that in higher organisms the enzyme may have evolved into a component of a glucose transport system. In order to obtain some information on its evolutionary background, the enzyme was purified to homogeneity from a variety of species, including some mammalian embryonic forms, and the physical and catalytic properties were compared. Mutarotase content is highest in mammalian kidneys, comprising from 0.15 to 0.29% of the total soluble protein of this tissue. The catalytic coefficients (moles of α-glucose converted to β-glucose per mole of enzyme per min) of the purified enzymes ranged from 2.8 x 105 for rabbit to 1.0 x 106 for the bovine kidney enzyme, the most active mutarotase so far isolated. On the basis of Km values for glucose, mutarotases fall into two distinct groups: those with a Km of 19 mm (bovine adult, sheep, sheep embryo, hog, hog embryo, mouse, gerbil, and dog) and those with a Km of 12 mm (human, rabbit, toadfish, yellow perch, chicken, catfish, and newborn calf). In the ox, three different kinetic forms of the enzyme which have otherwise indistinguishable physical properties are present at different stages of development (embryo calf Km 5 mm, calf (0 to 6 months) 12 mm, and adult 19 mm). All forms of the enzyme have the same substrate specificity and are inhibited equally by inhibitors of glucose transport such as phloridzin, phloretin, and diethylstilbestrol. The molecular sizes and asymmetries of the enzymes were measured by sedimentation velocity in the ultracentrifuge, electrophoretic mobility, and gel permeation chromatography. All were monomers of the same size as indicated by the following values for the molecular weights: human kidney (37,500), bovine adult kidney (37,300), calf kidney (37,300), lamb kidney (38,100), embryo calf liver (38,000), rabbit kidney (36,700), chicken kidney (35,900), yellow perch kidney (35,800), guinea pig kidney (38,100), and green pepper (38,300). The Stokes radii averaged 31.4 ± 1.3 A, indicating similar molecular asymmetries. The corresponding frictional ratios (f:f0) in buffers of low osmolarity were about 1.37 and the enzymes from all species underwent an identical molecular transition, converting to a more compact form with an f:f0 of 1.17 in buffers of physiological ionic strength. This transformation was also monitored by measuring the changes induced in the filtration of purified bovine kidney mutarotase through Diaflo membranes and was shown to be specifically reversed by substrate sugars. The prolonged evolutionary history and apparently stable physical and catalytic properties of the enzyme, when taken in conjunction with the lack of a requirement in glucose metabolism, indicate that some significant alternative function must have evolved. The osmotic transformation undergone by all mutarotases may be relevant to this function, since it suggests a possible mechanism whereby sugar transport could be coupled to the osmotic gradients which are established during solute transport in kidney and intestine.

The influence of pH and methylene blue on the pathways of glucose utilization and lactate formation in erythrocytes of man.

The influence of pH on the contributions of the Embden‐Meyerhof and of the oxidative pentose‐phosphate pathways in the utilization of glucose by human erythrocytes in the presence and absence of methylene blue were determined from yields of 14CO2 and [14C]lactate.In the absence of methylene blue both the NADP+ concentration and the phosphofructokinase are controlling factors. At pH 7.0 the oxidative pentose‐phosphate pathway accounts for nearly one‐half of the metabolic flux. Its contribution nearly vanishes at pH 8.2.In the presence of methylene blue the limitation by the NADP+ concentration disappears. At pH values of 7.4 and below the phosphofructokinase is completely inhibited and is circumvented for the formation of lactate. The limitation of the glucose influx resides in the hexokinase. At pH 8.2 both the Embden‐Meyerhof and the oxidative pentose‐phosphate pathway participate in the metabolic flux, since the inhibition of the phosphofructokinase is released.With methylene blue metabolic pools are formed. They are derived exclusively from the oxidative pentose‐phosphate pathway up to pH 7.5–7.6 and entirely from the Embden‐Meyerhof pathway at pH 8.2.

Pathways of glucose utilization in kidney homogenates of tuberculous and isoniazid-treated tuberculous guinea pigs

Male albino guinea pigs were infected by injection 0.1 ml of 7-day-old culture of Mycobacterium tuberculosis , strain H 37 Rv. The animals were divided into two groups: tuberculous and tuberculous-given-isoniazid. The latter group received isoniazid solution in lieu of drinking water from the 8th to the 30th day postinfection. The animals of both groups were sacrificed 30 days after infection. Kidney homogenates were studied for the utilization of glucose-1-C 14 and glucose-6-C 14. Some data have also been obtained on levels of succinic, isocitric and glucose-6-phosphate dehydrogenases and glucose-6-phosphatase. The utilization of both glucose-1-C 14 and glucose-6-C 14 and activities of succinic and isocitric dehydrogenases were markedly lowered in tuberculous homogenates as compared to controls. The levels of glucose-6-phosphate dehydrogenase and glucose-6-phosphatase were enhanced in infected homogenates. The ratios of C 14O 2 from glucose-1-C 14 to that from glucose-6-C 14 in tuberculous homogenates were approximately two and one-half times those of controls. This was apparently due to marked reduction in utilization of glucose-6-C 14 in comparison with that of glucose-1-C 14. Administration of isoniazid to tuberculous animals from the 8th to the 30th day postinfection revealed a normal utilization of both glucose-1-C 14 and glucose-6-C 14 by kidney homogenates. The levels of succinic and isocitric dehydrogenases were restored to control levels and those of glucose-6-phosphate dehydrogenase and glucose-6-phosphatase tended to lower to base levels. It is concluded that changes in levels of enzymes reported in this investigation are probably responsible for subnormal utilization of glucose by various pathways.

Metabolic Characteristics of Washed Boar Spermatozoa

Pathways of glucose and fructose utilization in washed boar spermatozoa were investigated, using glucose 1-14C, glucose 6-14C, glucose 3,4-14C, glucose-UL-14C and fructose UL-14C as tracers. Semen was washed twice at 650 g and resuspended in buffer solution at 37° C. Washed sperm were then incubated with labeled sugar for 15, 30, 45, 60, 90 or 120 min. using Warburg manometric techniques. Glucose 1-14C and glucose 6-14C sugars were paired, glucose 3,4-14C and uniformly labeled glucose were paired and uniformly labeled glucose was paired with uniformly labeled fructose. Twelve trials were run on the three pairs of sugars with four trials for each pair. Each trial was made up of 12 flasks. The respiratory 14CO2 ratios from glucose 1-14C to glucose 6-14C did not indicate the presence of the phosphogluconate pathway. The glycolytic pathway seems to be the major metabolic pathway for glucose utilization. Glucose had a significant sparing effect on fructose. There was no significant difference in oxygen consumption between glucose 1-14C, glucose 6-14C, glucose 3,4-14C and glucose UL-14C incubated cells. Lipid fractions were extracted from the sperm incubated with glucose 3,4-14C and separated with thin layer chromatography. Some of the fatty acids had a small amount of radioactivity, but not enough to show a pathway through the phosphogluconate shunt.

Metabolism of 14C-glucose in normal and foot-and-mouth disease virus infected bovine kidney culture cells

The contributions of the Embden-Meyerhof (EM), pentose, and nontriose phosphate pathways to glucose utilization in primary bovine-kidney cell cultures have been investigated by determining specific activities of lactic acid- 14C derived from glucose labeled in its 1,2, or 6 position. Pentose and nontriose phosphate pathways contributed about 4 per cent and at least 1 per cent respectively, to the total glucose metabolism. The EM pathway contribution could not be assessed directly from the data. However, assuming that the nontriose pathway is limited to 1 per cent, and that no other pathways for glucose utilization exist, the EM contribution would be about 95 per cent. Evidence supporting such assumptions is discussed. Cells infected with foot-and-mouth disease virus maintained the same pattern of glucose metabolism as did noninfected cells. The relative molar specific activity of lactic acid as compared to glucose varied from 0.3 to 0.5 depending upon the kidney tissue from which the primary cell cultures were derived. The contribution of nonlabeled precursors to this variability is discussed. Pretreatment of the culture cells, i.e., starvation, did not alter this effect. Total recovery experiments demonstrated a predominant conversion of glucose to lactic acid for both 3- and 18-hr incubation periods. Intracellular components and respired CO 2 were only slightly labeled.

Glucose uptake by HeLa cells as influenced by insulin

A simple system has been described in which insulin stimulation of glucose uptake by HeLa cells can be measured after a three hour incubation in a solution of bicarbonate buffered saline. The glucose uptake of HeLa cells in the presence and absence of insulin in the above medium was compared to that occurring in more complex media. The influence of temperature and osmotic pressure on glucose uptake and insulin effect in this simple medium was also studied. In these experiments, there did not appear to be any relationship between the insulin stimulation of glucose uptake and the amount of glucose uptake occurring in the absence of insulin. These findings are best explained in terms of two independent pathways of glucose utilization, one insulin dependent and the other non-responsive to insulin.

The localization of enzyme activity in the electric organ of Electrophorus electricus (L)

The main oxidative enzyme activities in the Sachs organ of Electrophorus electricus, whether related to the tricarboxylic acid cycle or to the glycolytic pathways, are concentrated in the posterior portion of the electroplate. No evidence could be found for the existence of an alternative (pentose cycle) pathway of glucose utilization. Phosphorylase is present exclusively in the anterior portion of the electroplate. It is suggested that the neutral polysaccharide (glycogen) present in the anterior portion of the electroplate acts as the main source of energy for maintenance of electric potential in the membrane. Its breakdown product (glucose-1-phosphate) could diffuse from the anterior portion across the electroplate to be utilized at the active posterior membrane.