Rate Of Glycogen Accumulation Research Articles

Regulation of glycogen accumulation in L6 myotubes cultured under optimized differentiation conditions.

The differentiation of the L6 myogenic cell line was enhanced by the addition of dexamethasone, retinoic acid, insulin-like growth factor I (IGF-I), and creatine. Spontaneous contractions appeared from day 10 or 11 and persisted to day 14 or 15. Glucose transport was increased by insulin (100 nM) and IGF-I (5 nM) by approximately 60%. The highest level of glycogen was measured in myotubes differentiated under the influence of a combination of 5 nM dexamethasone, 100 nM retinoic acid, 5 nM IGF-I, and 10 mM creatine with glucose as substrate. The glycogen accumulation rate was constant from 0 to 2 h of incubation and decreased gradually to zero at 4 h. From 0 to 0.5 h of the glycogen accumulation, the glycogen synthase a (GSa) activity was 30-35% of the total activity, with a subsequent gradual decline to 2.5% after 6 h. The glycogen phosphorylase a (GPha) activity was constant at approximately 80% from 0 to 0.5 h, increasing to approximately 100% after 6 h. The activity ratio of GSa to GPha decreased about sixfold without significant change in the rate of glycogen accumulation. This indicates that factors other than phosphorylation/dephosphorylation play a decisive role in the regulation of glycogen metabolism in L6 myotubes. Intracellular glucose (glucosei) and glucose 6-phosphate (G-6-P) may be such factors. The observed values of these parameters may in fact explain an activation of GSa (G-6-P) and an inhibition of GPha (glucosei).

Coordinate genetic regulation of glycogen catabolism and biosynthesis in Escherichia coli via the CsrA gene product

The carbon storage regulator gene, csrA, encodes a factor which negatively modulates the expression of the glycogen biosynthetic gene glgC by enhancing the decay of its mRNA (M. Y. Liu, H. Yang, and T. Romeo, J. Bacteriol. 177:2663-2672, 1995). When endogenous glycogen levels in isogenic csrA+ and csrA::kanR strains were quantified during the growth curve, both the rate of glycogen accumulation during late exponential or early stationary phase and its subsequent rate of degradation were found to be greatly accelerated by the csrA::kanR mutation. The expression of the biosynthetic genes glgA (glycogen synthase) and glgS was observed to be negatively modulated via csrA. Thus, csrA is now known to control all of the known glycogen biosynthetic genes (glg), which are located in three different operons. Similarly, the expression of the degradative enzyme glycogen phosphorylase, which is encoded by glgY, was found to be negatively regulated via csrA in vivo. The in vitro transcription-translation of glgY was also specifically inhibited by the purified CsrA gene product. These results demonstrate that localization of glycogen biosynthetic and degradative genes within the Escherichia coli glgCAY operon facilitates their coordinate genetic regulation, as previously hypothesized (T. Romeo, A. Kumar, and J. Preiss, Gene 70:363-376, 1988). The csrA gene did not affect glycogen debranching enzyme, which is now shown to be encoded by the gene glgX.

Physiology, Biochemistry and Genetics of Bacterial Glycogen Synthesis

The chapter presents the current views and concepts of regulation of enzyme activity and expression on bacterial glycogen synthesis. The structural genes of the glycogen biosynthetic enzymes of Escherichia coli and of Salmonella typhimurium are isolated and more information bearing on the genetic regulation of glycogen synthesis in E. coli is accumulated. Many bacterial species accumulate glycogen in either stationary phase or under limited growth conditions with excess carbon in the media. For several bacterial species ( E. coli, Agrohactcrium tumcfacicws, Arthrohacter, Enterohacter aerogenes) , it has been shown that the rate of glycogen accumulation in stationary phase increases when growth ceases due to depletion of a nutrient required for growth. The site of regulation of glycogen synthesis in bacteria is at the ADPglucose pyrophosphorylase step. Many of the physical and chemical properties of the bacterial ADPglucose pyrophosphorylases are summarized. Effects of cAMP and cAMP receptor protein and effects of ppGpp on the expression of glycogen biosynthetic genes are discussed.

Glycogen Accumulation and the Induction of Nitrogenase Activity in the Heterocyst-forming Cyanobacterium Anabaena variabilis

Summary: Anabaena variabilis (ATCC 29413) grown in batch cultures for 2 d exhibited rapid glycogen synthesis upon dilution of the cell suspension. The cellular polysaccharide concentration attained a maximum after 9-12 h growth in fresh medium and decreased thereafter. The growth rate, the rate of glycogen accumulation and the maximum amount of glycogen increased when light intensity was increased. Accumulation occurred with both N2 and ammonia as N-sources. In cultures grown in the presence of ammonia, the increase in the cellular C-fraction upon dilution caused neither induction of nitrogenase nor heterocyst formation. However, ammonia depletion during subsequent growth gave rise to a second accumulation of glycogen followed by differentiation. Thus, in this phototroph, glycogen is synthesized without subsequent differentiation following an increase in average irradiation as long as the N-supply is maintained. Glycogen synthesis following N-depletion, however, is accompanied by induction of nitrogenase.

Persistent increase in glucose uptake by rat skeletal muscle following exercise.

The effect of a bout of exercise on glucose uptake and glycogen synthesis in skeletal muscle was examined using a perfused rat hindlimb preparation. Rats were subjected to a bout of swimming. The exercise stress was moderate as reflected in a reduction of muscle glycogen concentration of only 50%. Glucose uptake and glycogen synthesis were measured in perfused hindlimb muscles for a 30-min period beginning approximately 60 min following the exercise. The rate of glucose uptake in the absence of insulin was 10-fold higher in hindlimbs of exercised animals than in the controls. The rate of glucose uptake was also higher in exercised than in control muscles in the presence of 50 microunits/ml or 10 mU/ml of insulin, but these differences were smaller than that found in the absence of insulin. Conversion to glycogen was the major pathway for disposal of the glucose taken up by muscle. The rate of glycogen accumulation in the exercised plantaris muscles was greater than in the control muscles both in the absence and presence of insulin.

Glycogen synthesis from lactate in the three types of skeletal muscle.

Lactate utilization by skeletal muscle was studied in the perfused rat hindlimb. At lactate concentrations above 4 mu, the hindlimb consistently removed lactate from the perfusion medium. At the concentrations examined (up to 26 mu), the rate of lactate uptake was proportional to lactate concentration. When the hindlimb was perfused with medium containing 12 mu lactate as the only substrate, a rapid increase in glycogen occurred in the fast-twitch red and fast-twitch white types of muscle. In contrast, the rate of glycogen accumulation in the slow-twitch red type of muscle was so slow as to be of questionable physiological significance. [W]Lactate was rapidly incorporated into glycogen in the plantaris muscle which is composed predominantly (about 94%) of fast-twitch fibers, while there was little incorporation of [14C]lactate into glycogen in the soleus muscle which consists predominantly of slow-twitch red fibers. Measurement of fructose-1,6-bisphosphatase activity provided an explanation for the very slow rate of lactate conversion to glycogen in slow-twitch red muscle. It was found that in contrast to the fast-twitch red and white types of muscle, the slow-twitch red soleus muscle has an extremely low level of fructose1,6-bisphosphatase activity. There was a 24% inhibition of lactate uptake, and the amount of [14C]lactate incorporated into plantaris muscle glycogen was reduced by 30%, when 8.5 mu glucose and insulin were included in the perfusion medium. However, neither the rate of lactate uptake nor the rate of glycogen accumulation was affected by a high concentration of insulin alone.

Glycogen synthetase and the control of glycogen synthesis in the cellular slime mould Dictyostelium discoideum during the growth (myxamoebal) phase.

1. Myxamoebae of the cellular slime mould Dictyostelium discoideum Ax-2 that are grown in axenic medium containing 86mm-glucose have seven times the glycogen content of the same myxamoebae grown in the same medium but lacking added carbohydrate. 2. During the transition from the exponential to the stationary phase of growth in axenic medium containing glucose myxamoebae preferentially synthesize glycogen and can have as much as three times the glycogen content during the stationary phase as they have during the exponential phase of growth. 3. The rate of glycogen degradation by myxamoebae is, under all conditions of growth, small compared with the rate of glycogen accumulation and the changes in glycogen content thus reflect altered rates of glycogen synthesis. 4. There is no correlation between the rate of glycogen synthesis by myxamoebae and the glycogen synthetase content of the myxamoebae. 5. The activity of glycogen synthetase of D. discoideum is inhibited by a physiological concentration of ATP and this inhibition is overcome by glucose 6-phosphate. Both effects are especially marked at physiological concentrations of UDP-glucose. 6. The rate of glycogen accumulation by myxamoebae growing exponentially in axenic media can be satisfactorily accounted for in terms of the known intracellular concentrations of glucose 6-phosphate, UDP-glucose and glycogen synthetase. The rate-limiting factors controlling glycogen synthesis by the myxamoebae are apparently the substrate (UDP-glucose) and effector (glucose 6-phosphate and ATP) concentrations rather than the amount of the enzyme.

Endocrine control of yolk sac membrane glycogen in the developing chick embryo: II. Effects of hypophysectomy

The effect of hypophysectomy upon glycogen accumulation by the yolk sac membrane of the developing chick embryo has been studied. Animals were hypophysectomized at 33- to 38-hours of incubation by the “partial decapitation” method of Fugo (1940), Yolk sac membranes were collected at 24-hour intervals from day 9,5 through 19.5 of incubation. Glycogen levels were determined by the anthrone method ( Carroll et al., 1956 ). Although hypophysectomy produces no change in glycogen levels of yolk sac membranes of 9.5-, 10.5-, and 11.5-day embryos, by day 12.5 of incubation a statistically significant reduction in rate of glycogen accumulation has occurred. Glycogen levels of operated animals on days 13.5, 14.5, 15.5, 16.5, and 17.5 of incubation remain at the 12.5-day level. The period of 15.5 to 19.5 days of incubation is characterized by a sharp increase and decline in yolk sac membrane glycogen levels in normal animals. This increase and reduction is reflected in hypophysectomized animals, however it is out of phase by 1 day. A single administration of cortisone acetate on day 13.5 to pituoprivic embryos raises glycogen levels above normal on days 14.5 and 15.5 of incubation. The data demonstrate that the developing chick embryo does exert hormonal control over metabolic events within this membrane.