A new assay of phosphorylase based on the filter paper technique

Sensitive assay of glycogen phosphorylase activity by analysing the chain-lengthening action on a Fluorogenic [corrected] maltooligosaccharide derivative

The action of glycogen phosphorylase (GP) is essentially reversible, although GP is generally classified as a glycogen-degrading enzyme. In this study, we developed a highly sensitive and convenient assay for GP activity by analysing its chain-lengthening action on a fluorogenic maltooligosaccharide derivative in a glucose-1-phosphate-rich medium. Characterization of the substrate specificity of GP using pyridylaminated (PA-) maltooligosaccharides of various sizes revealed that a maltotetraosyl (Glc(4)) residue comprising the non-reducing-end of a PA-maltooligosaccharide is indispensable for the chain-lengthening action of GP, and PA-maltohexaose is the most suitable substrate for the purpose of this study. By using a high-performance liquid chromatograph equipped with a fluorescence spectrophotometer, PA-maltoheptaose produced by the chain elongation of PA-maltohexaose could be isolated and quantified at 10 fmol. This method was used to measure the GP activities of crude and purified GP preparations, and was demonstrated to have about 1,000 times greater sensitivity than the spectrophotometric orthophosphate assay.

Assay for enzyme activity by following the absorbance change of pH-indicators

Based on the absorbance change of indicators with the concentration of hydrogen ion released from an enzyme-catalyzed reaction, a convenient colorimetric method was established for the assay of acidic phospholipase A2 and glycogen phosphorylase b. Brilliant yellow and bromothymol blue were chosen as indicators for assays of acidic phospholipase A2 and glycogen phosphorylase b by following the absorbance changes at 495 and 615 nm, respectively. The method is simple, sample-saving, sensitive and valid for a wide range of enzyme concentrations. It can be extended for assaying other enzymes catalyzing reactions with hydrogen ion concentration changes.

Glycogen phosphorylase isoenzymes from hepatoma 3924A and from a non-tumorigenic liver cell line. Comparison with the liver and brain enzymes

Glycogen phosphorylase isoenzymes were isolated from normal rat liver, rat brain, the glycogen-poor Morris hepatoma (MH) 3924A, and the glycogen-rich non-tumorigenic liver cell line C1I. Electrophoretic and immunological characterization of the enzymes showed that tumour and C1I cells expressed a phosphorylase isoform similar to the brain type; the liver type was not detectable. All enzymes were obtained as dimers; the Mr of the subunits was 96,000 (liver), 93,000 (brain and MH 3924A) and 92,000 (C1I). Isoelectric focusing revealed a main band of pI 6.34 for liver phosphorylase a, pI 5.67 for the enzymes from MH 3924A and brain, and pI 5.68 for C1I phosphorylase. Partial kinetic characterization of the AMP-independent forms of the isoenzymes yielded Km values for glucose 1-phosphate of 3.5 +/- 0.5 mM (liver), 3.9 mM (brain), 1.9 +/- 0.3 mM (MH 3924A) and 2.5 +/- 0.5 mM (C1I); Km values for glycogen were 0.4 mM (liver) and 0.3 mM (MH 3924A and C1I), calculated as glucose equivalents. The AMP-independent phosphorylase was inhibited by glucose 6-phosphate (Glc6P) with Ki values of 0.32 +/- 0.03 mM (C1I), 0.50 +/- 0.04 mM (MH 3924A) and approximately 5 mM (brain). The inhibition could be abolished by 1 mM-AMP, indicating that AMP and Glc6P may partially compete for the same site on the protein. Liver phosphorylase a was not inhibited by up to 25 mM-Glc6P. In contrast with liver and brain isoenzymes, phosphorylase from the cell lines was not affected by NaF and Na2SO4. The data show that both the hepatocellular carcinoma and the non-malignant immortalized liver cells express a phosphorylase isoform different from the liver type. Furthermore, there is some evidence that the enzyme from MH 3924A and C1I cells is distinct from brain phosphorylase a, in spite of electrophoretic and immunological resemblance, and that this isoenzyme is subject to altered metabolic regulation.

Glucose 6-phosphate plays a central role in the regulation of glycogen synthesis in a glycogen-storing liver cell line

Two substrains of the epithelial liver cell line C1I, one storing large amounts of glycogen, the other one being very poor in glycogen were used as a model for studying glycogen synthesis. The glycogen content of glycogen-rich cells doubled during the proliferative phase and remained high in plateau phase although glycogen synthase I activity was not significantly altered during growth cycle and was too low to account for the increase in glycogen. However, the activity of the glucose 6-phosphate (Glc6-P)-dependent synthase rose continuously during growth cycle, and intracellular Glc6-P-concentration increased about 10-fold in log phase cells to 0.72 mumol g-1 wet weight. A0.5 of synthase for Glc6-P was 0.79 mM. It was also found that in contrast to the enzyme from normal liver, glycogen phosphorylase a from C1I cells was inhibited by Glc6-P, the apparent Ki being 0.45 mM. It was concluded that glycogen accumulation in C1I cells was due to stimulation of synthase and inhibition of phosphorylase by Glc6-P. Findings from the glycogen-poor cell line which revealed similar specific activities of synthase and phosphorylase but only low Glc6-P (0.056 mumol g-1 wet weight) supported this conclusion. Addition of glucose to starved cells resulted in a transient activation of synthase in both cell lines. Net glycogen synthesis, was, however, only observed in the cells with a high Glc6-P-content. Thus, modulation of synthase and phosphorylase by Glc6-P and not activation/inactivation of the enzymes seems to play a predominant role in glycogen accumulation in this cell line.

Insulin controls key steps of carbohydrate metabolism in cultured HT29 colon cancer cells

Effects of insulin on key steps of carbohydrate metabolism were investigated in cultured HT29 colon cancer cells by two different approaches, i.e. incubation of the cells either in the absence or in the presence of glucose in the medium. In glucose-deprived cells, insulin decreased glycogen breakdown, but did not affect polysaccharide levels when glucose was present. Glycogen synthase became activated after insulin treatment in both conditions, even though the activation was more evident when glucose was omitted. No effect on glycogen phosphorylase activity was evident under our experimental conditions. In cells incubated with glucose, the hormone stimulated in a dose-dependent manner the rates of glucose uptake and lactate release. Concomitantly with the increase in glycolytic rate, insulin caused a strong increase in fructose 2,6-bisphosphate. This effect was not observed in the absence of glucose. It is concluded that the carbohydrate metabolism of cultured HT29 cells responds to insulin, making this biological model suitable for investigations in vitro on the mechanism of insulin action.

Characteristics of acetylcholine-induced phosphorylase a activity in uterine segments as a substitute for contractile response to acetylcholine

Studies were made on whether the ACh-induced phosphorylase a activity in isolated rat uterine muscle segments could be used as a substitute for the contractile response to ACh. This ACh-induced phosphorylase a activity was dependent upon the concentration of ACh and was inhibited by atropine, suggesting that it was linked to muscarinic ACh receptors. Both extracellular calcium and an increase of the intracellular calcium concentration were needed for its activation by ACh. Ca2+-antagonists such as Co2+, diltiazem, nitrendipine and verapamil inhibited the ACh-induced activity, suggesting that the activation by ACh required the influx of calcium ions into the uterine muscle through Ca2+-antagonist sensitive Ca2+ channels. The IC50 values of CoCl2, diltiazem, nitrendipine and verapamil on the ACh-induced phosphorylase a activity were 3.4 x 10(-3) M, 2.5 x 10(-4) M, 2.5 x 10(-5) M and 1.1 x 10(-4) M, respectively. These values were comparable with the IC50 values of these Ca2+-antagonists on the contractile response of isolated rat uterine muscle segments to 3 x 10(-4) M ACh. The inhibitory effects of Co2+, nitrendipine and verapamil, but not diltiazem, on ACh-induced phosphorylase a activity were attenuated by higher concentrations of CaCl2 (0.36 to 2 mM). These findings suggested that the ACh-induced phosphorylase a activity in isolated rat uterine muscle segments could be used as a substitute for the contractile response to ACh.

Activity of glycogen synthase and phosphorylase and glucose 6-phosphate content in renal clear cell carcinomas

Eleven renal clear cell carcinomas were investigated with regard to their glycogen and glucose 6-phosphate (G6P) content and the activities of glycogen synthase and phosphorylase. Compared to normal cortex from the same kidneys, all tumours revealed increased glycogen and G6P content. The activities of phosphorylase a and b as well as of synthase R and D were also increased. Synthase I activity, however, was reduced. It was concluded that in these tumours glycogen synthesis may preferentially be catalyzed by synthase R which is activated by G6P. These findings agree with those in some other glycogenotic tissues and support the concept that an accumulation of G6P is associated with excessive storage of glycogen in preneoplastic and neoplastic lesions.

Phosphorylase a activity as an indicator of neutrophil activation by chemotactic peptide

The activity of glycogen phosphorylase, an enzyme that is activated by both cAMP and calcium, was used as an indicator of the state of the cytoplasm after chemotactic stimulation of polymorphonuclear leukocytes (neutrophils). The activity of the enzyme showed a clear dependence on cytoplasmic calcium. Addition of the calcium ionophore A23187 caused a 4-5-fold increase in activity of phosphorylase a. In the absence of external Ca2+, A23187 caused only brief transient activation of phosphorylase; probably reflecting release of sequestered intracellular Ca2+. Addition of the chemotactic peptide N-formylnorleucylleucylphenylalanine (FNLLP) caused a transient 2-3-fold activation of the enzyme. The dose-dependence of activation by FNLLP showed a peak at 10(-8) M, near the Kd of the receptor for FNLLP. The phosphorylase activity peaks by 90 s and then declines, returning to basal levels by 20 min after stimulation with 10(-8) M peptide and by 60 min with 10(-7) M peptide. This finding suggests that the cells do not need to maintain elevated cytoplasmic calcium levels to exhibit stimulated locomotion. Thus, if calcium continues to modulate the motility, there either must be highly localized changes that are not detected in measures of the total cytoplasm, or the sensitivity to calcium must be variable such that basal levels are sufficient to maintain locomotion. Cells loaded with the fluorescence calcium probe quin2 (0.6 mM) in the presence or absence of external Ca2+ had elevated phosphorylase levels before addition of FNLLP. Thus, the presence of quin2 may alter the cytoplasmic Ca2+ level, and it clearly alters some aspects of the neutrophil physiology. Phosphorylase a appears to be a sensitive, nonperturbing indicator of the cytoplasmic calcium levels.

Purification and properties of glycogen synthase I from bovine polymorphonuclear leucocytes

Glycogen synthase I was purified from bovine polymorphonuclear leucocytes (PMNs) by a procedure involving concanavalin A-Sepharose affinity chromatography. The purified glycogen-bound glycogen synthase I had a specific activity of 9.83 U/mg protein and the glycogen free enzyme 21 U/mg protein. Molecular ratio of the native enzyme and the subunit were 340 K and 85 K respectively. After phosphorylation by the catalytic subunit of cAMP-dependent protein kinase the phosphorylated sites were studied using high-performance liquid chromatography (HPLC) of the tryptic 32P-peptides. The enzyme was phosphorylated at three different sites with retention times identical to site 1a, site 1b, and site 2 from rabbit skeletal muscle glycogen synthase.

Activity of enzymes related to carbohydrate metabolism in the HT 29 colon adenocarcinoma cell line and tumor

Activity of several enzymes of the glycogen and carbohydrate metabolism is studied in HT 29 colon adenocarcinoma cell line and in HT 29 tumors developed in nude mice, by reference to the normal human colon mucosa. Activity of glycogen synthase, glycogen phosphorylase, pyruvate kinase, fructose-1,6-diphosphatase, glucose-6-phosphate dehydrogenase and lactate dehydrogenase is found to be increased in both the cultured cells and the tumors. It indicates that the biochemical strategy of malignant cells, due to the neoplastic transformation process, involves specific changes in the carbohydrate metabolism of tumor as well as in vitro growing correspondent cell line.

Chromatographic characteristics and subcellular localization of synthase phosphatase, phosphorylase phosphatase and histone phosphatase in human polymorphonuclear leukocytes

Synthase phosphatase, phosphorylase phosphatase and histone phosphatase activity in a leukocyte homogenate were found to have different sedimentation characteristics: both synthase phosphatase and phosphorylase phosphatase activity are associated with the microsomal fraction, while the majority of histone phosphatase activity (75-85%) was found in the cytosol. Synthase phosphatase, phosphorylase phosphatase and histone phosphatase activities accompanying the microsomal fraction are readily solubilized by 0.3% Triton X-100. When the solubilized microsomal enzymes were chromatographed on Sephadex G-200, the majority of synthase phosphatase, phosphorylase phosphatase and histone phosphatase activity migrated in single peaks corresponding to apparent molecular weights of 380 000, 250 000 and 68 000, respectively. A minor peak of 30 000, which had phosphatase activity against all three substrates was also obtained. Ethanol treatment resulted in solubilization and dissociation of the three phosphatase activities. It was found that although ethanol treatment resulted in a 4-fold increase of phosphorylase phosphatase activity, histone phosphatase activity was decreased (by 60%), while synthase phosphatase activity remained stable. Similar results were obtained when ethanol treatment was performed on the 17 000 X g supernatant. Chromatography of the ethanol-treated microsomes (or homogenate) on Sephadex G-200 showed that the phosphatase activity towards synthase D, phosphorylase a and phosphohistone coincided a Mr 30 000 species. Heat treatment of the Mr 30 000 peak resulted in dissociation of synthase phosphatase and phosphorylase phosphatase activity. Synthase phosphatase was inhibited by phosphorylase a in a kinetically non-competitive manner while histone phosphatase activity was not inhibited by synthase D (8.5 unit/ml) or by phosphorylase a (12 unit/ml).

Turbidimetric method for determination of glycogen phosphorylase activity and its use for estimation of equilibrium position of enzymic reaction

A turbidimetric method has been developed for the continuous monitoring of the enzyme reaction catalyzed by glycogen phosphorylase. This method is based on the registration of the turbidity of glycogen solution at wavelengths above 300 nm. It has been shown that the increase in the turbidity is strictly proportional to the quantity of glucose 1-phosphate formed during the enzyme reaction. The method has the advantage of continuity, and it is suitable for determining the initial rate of catalytic synthesis or degradation of glycogen in a relatively simple and fast way. The kinetic experiments may be carried out under various conditions. The method of calculation of the overall equilibrium constant of the enzyme reaction catalyzed by glycogen phosphorylase has been elaborated. This method is based on the analysis of the dependence of the initial rate of the enzymic reaction on the proportion of the substrate of the forward reaction: [Pi]/( [Pi] + [G-1-P] ).

Activity of glycogen metabolizing enzymes in glucose deprived HT 29 adenocarcinoma cell-line

When deprived of glucose, the cultured HT 29 adenocarcinoma cells are able to mobilize their glycogen within 4 hours. Glycogen phosphorylase is strongly activated during the first hour of glucose starvation. Then, while the a/a + b ratio for phosphorylase is declining, glycogen synthase is partially converted into the a form; this conversion does occur although glycogen phosphorylase is far from being totally inactivated. After 4 hours, activity of both a and total forms of glycogen synthase decrease. Cell UDP-glucose and glucose-6-P levels are declining during the 24 hours period of glucose starvation. Cell ATP content decreases by only 50 percent over the same period of time.

Energy metabolism of human neutrophils during phagocytosis

Detailed quantitative studies were performed on the generation and utilization of energy by resting and phagocytosing human neutrophils. The ATP content was 1.9 fmol/cell, was constant during rest, and was not influenced by the presence or absence of glucose in the medium. The intracellular content of phosphocreatine was less than 0.2 fmol/cell. In the presence of glucose, ATP was generated almost exclusively from lactate produced from glucose taken up from the surrounding medium. The amount of lactate produced could account for 85% of the glucose taken up by the cells, and the intracellular glycosyl store, glycogen, was not drawn upon. The rate of ATP generation as calculated from the rate of lactate production was 1.3 fmol/cell/min. During phagocytosis, there was no measurable increase in glucose consumption or lactate production, and the ATP content fell rapidly to 0.8 fmol/cell. This disappearance of ATP was apparently irreversible since no corresponding increase in ADP or AMP was observed. It therefore appears that this phagocytosis-induced fall in ATP concentration represents all the extra energy utilized in human neutrophils in the presence of glucose. In the absence of glucose, the rate of ATP generation in the resting cell was considerably smaller, 0.75 fmol/cell per min, as calculated from the rate of glycolysis, which is sustained exclusively by glycogenolysis. Under this condition, however, phagocytosis induces significant enhancement of glycogenolysis and the rate of lactate production is increased by 60%, raising the rate of ATP generation to 1.2 fmol/cell per min. Nonetheless, the ATP content drops significantly from 1.9 to 1.0 fmol/cell. Neutrophils from patients with chronic granulomatous disease have the same rate of glycolysis and the same ATP content as normal cells, thus confirming that the defective respiration of these cells does not affect their energy metabolism.

Metabolic type of muscles of the sheep. III. evolution with age and influence of sex

Myofibrillar ATPase activity (in the presence of Ca2+ and Mg2+), activities of various glycolytic and mitochondrial enzymes, and haemin iron, glycogen, ATP and lactic acid levels were determined in the heart and five skeletal muscles of the sheep as a function of age and sex. During growth from 2 to 13 months, ATPase activity remained stable whereas most mitochondrial and glycolytic activities tended to decrease, particularly between 2 and 6 months. The isoenzyme composition of lactic dehydrogenase evolved markedly, with in particular a rise in the percentage of M4. Haemin iron level rose from 6 months. These modifications occurred in most of the skeletal muscles but rarely in the heart. Glycogen and ATP decreased progressively between 2 and 13 months. Overall, results indicated a regression of the metabolic differentiation among muscles between 2 and 13 months, particularly marked before 6 months. At 3 and 7 months, sex had practically no influence on the enzyme activities studied.

Activation of the glycogenolytic cascade in human polymorphonuclear leucocytes by different phagocytic stimuli

Human polymorphonuclear leucocytes were found to respond to activation by immunoglobulin opsonized latex particles and to complement opsonized zymosan particles with a rapid transient increase in cAMP concentration, dissociation of the cAMP dependent protein kinase, activation of glycogen phosphorylase and glycogen break down. However, since phosphorylase kinase was not activated, the activation of phosphorylase is believed to be secondary to non-covalent activation of phosphorylase kinase by Ca2+. Activation by the soluble stimulator phorbol myristate acetate resulted in activation of phosphorylase and glycogen break down, whereas no changes in cAMP concentration, protein kinase activity, or phosphorylase kinase activity were observed. The activation of phosphorylase is ascribed to an increase in cytosolic Ca2+ concentration. The response to stimulation by zymosan was strongly inhibited by ethylene glycol-bis-(beta-aminoethyl ether)-N,N1-tetraacetic acid, which did not affect stimulation by either latex particles or phorbol myristate acetate. The same differential effect of ethylene glycol-bis(beta-aminoethyl ether)-N,N1-tetraacetic acid was observed when the response of the cells was measured as increase in oxygen consumption and activation of the hexose monophosphate shunt.

Metabolic types of muscle in the sheep: I. Myosin ATPase, glycolytic, and mitochondrial enzyme activities

The metabolic characteristics of 12 skeletal muscles of the sheep were studied. Glycolytic activities (hexokinase, glycogen synthetase I and D, phosphorylase a and b, phosphofructokinase) were measured. Myofibrillar ATPase activity was evaluated. Oxygen consumption, respiratory control and carnitine palmityl transferase, isocitrate dehydrogenase, succinate dehydrogenase and cytochrome oxidase activities were measured in isolated mitochondria. Three metabolic types could be distinguished; (1) essentially oxidative slow twitch muscles, typified by the supraspinatus and infraspinatus, having low ATPase activity, (2) fast twitch red muscles, typified by the longissimus dorsi and the semimembranosus, having a higher ATPase activity and both high oxidative and high glycolytic activity, and (3) essentially glycolytic fast twitch muscles, typified by the tensor fascia lata and the semitendinosus, having the highest ATPase activity.

Effect of glycogenolytic agents on glycogen synthase activity in polymorphonuclear leukocytes. Evidence for a Ca2+-mediated regulation of glycogen synthase activity

Human polymorphonuclear leukocytes were found to respond to the beta-receptor activators, adrenalin and isoproterenol, with a rapid transient increase in cyclic AMP, activation of cyclic AMP-dependent protein kinase, phosphorylase kinase, deactivation of glycogen synthase and glycogen breakdown. This response was unaffected by the presence of 10 mM EGTA. Incubation of leukocytes with phorbol myristate acetate, which stimulates the hexose monophosphate shunt by a Ca2+ mediated mechanism, resulted in activation of phosphorylase without affecting cyclic AMP-dependent protein kinase or phosphorylase kinase activity, thus indicating a Ca2+-mediated activation of phosphorylase. This was, however, unaffected by EGTA. Prolonged incubation with phorbol myristate acetate was found to result in a parallel activation of phosphorylase and glycogen synthase secondary to a pronounced depletion of cellular glycogen. Addition of glucose to polymorphonuclear leukocytes resulted in total conversion of phosphorylase a to the b form and activation of glycogen synthase, however, when EGTA was included, the response to glucose was greatly amplified, thus indicating the synthase conversion is regulated by Ca2+ sensitive mechanisms which do not involve phosphorylase kinase. Addition of adrenalin to cells previously activated by glucose resulted in an increase in the concentration of cyclic AMP and activation of cyclic AMP-dependent protein kinase but deactivation of synthase was not effectuated under these conditions.

Effect of supplemental dietary chromium or nicotinic acid on carbohydrate metabolism during basal, starvation, and refeeding periods in poults

A series of experiments were conducted with turkey poults to ascertain the effects of supplemental chromium or excess of nicotinic acid on growth and carbohydrate metabolism. A 23% protein starter diet was selected to emphasize the effect of chromium under basal, starvation for 48 hr, and refeeding periods. Thirty percent protein diets were also used to determine if the effects were compounded by protein levels. Supplemental chromium (20 ppm) significantly increased (P less than .05) weight at 3 weeks of age of poults consuming 23% protein diets, while an additional 250 ppm of nicotinic acid had little effect on poult weight at 3 weeks (P greater than .05). Supplemental chromium did not increase (P greater than .05) feed consumption of poults consuming both 23 and 30% protein diets. Supplemental chromium increased liver glycogen at 3 weeks of age and following refeeding after the 48 hr fast (P less than .05). Blood glucose was significantly affected by starvation-refeeding (P less than .05) but was not affected by either chromium or nicotinic acid. Supplemental chromium increased (P less than .01) active glycogen synthetase, while nicotinic acid increased (P less than .01) active phosphorylase at both protein levels. Synthetase was not decreased by starvation but was increased (P less than .01) by refeeding regardless of protein level fed. Phosphorylase was not affected by a starvation-refeeding regimen. Chromium supplementation increased in the vitro incorporation of (14C) glucose into glycogen during basal, starvation and refeeding periods (P less than .01), again, regardless of protein level.

Increased hepatic glycogen synthetase and decreased phosphorylase in trained rats

Rats were either physically trained by a 12 wk swimming program or were freely eating or weight matched, sedentary controls. Trained rats had a higher relative liver weight and total hepatic glycogen synthetase (EC 2.4.1.11) activity and a lower phosphorylase (EC 2.4.1.1) activity than the other groups of rats. These changes may partly explain the demonstrated training-induced increase in glucose tolerance. None of the findings could be ascribed to differences in foold intake or body weight.

Phosphorylase kinase from human polymorphonuclear leukocytes

Phosphorylase kinase from human polymorphonuclear leukocytes was investigated in a gel filtered crude preparation (17,000 x g supernatant). It was found to exist in two forms, one (the phosphorylated form) more active than the other (the dephosphorylated form). Interconversion between the two forms was carried out by a cyclic AMP dependent protein kinase and phosphoprotein phosphatase, respectively. The ratio of activity measured at pH 8.0 and 6.0 was 0.36 for the non-activated and 0.83 for the activated form, which is in contrast to the behaviour of phosphorylase kinase from muscle. Km app for the substrate phosphorylase b was 650 U/ml and 85 U/ml for the non-activated and activated form, respectively, whereas Km app for ATP was 0.03 mM and identical for the two forms. The non-activated form of phosphorylase kinase was activated by Ca2+ in the range 10(-7)--5 . 10(-6) M, which may have physiological importance, whereas the activated form was insensitive to variations in Ca2+ concentration between 10(-9) and 10(-3) M.

Modifications of the activities of key enzymes and intracellular levels of cyclic nucleotides, in correlation with the glyogen deposition in a cultured hepatoma cell line

Glycogen accumulation in growing cultures of ZHC cells (originally derived from the Zajdela ascitic hepatoma) is accompanied by an increase in glycogen synthetase (E.C. 2.4.1.11) and phosphorylase (E.C. 2.4.1.1) activities. Essentially the synthetase b and the phosphorylase a are involved in this process. The glycogen accumulation in ZHC cells us preceeded by a noticeable peak of cAMP, whereas cGMP rises early after replating and then decreases simultaneously with the growth rate. The present results suggest that these cultured hepatoma cells undergo throughout every passage an induction process involved in glycogen synthesis storage. Since the original ascites cells growing in vivo (which lack glycogen) and the cultured ZHC cells exhibit similar glycogen synthetase and phosphorylase activities, the resurgence of the glycogenic function (Staedel and Beck, 1978) in the in vitro cultureed cells does not seem related to a change in these two enzymes. By contrast, the high cyclic nucleotide levels in the cultured cells, as compared to those in the ascites cells, offer a possible explanation.

The role of calcium and cyclic adenosine 3',5'-monophosphate in the regulation of glycogen metabolism in phagocytozing human polymorphonuclear leukocytes

Incubation of human polymorphonuclear leukocytes in a glucose-free Krebs-Ringer bicarbonate buffer for 2 h resulted in glycogen depletion, decreased phosphorylase activity and increased synthase-R activity. Addition of dialyzed latex particles to starved leukocytes revealed a very rapid ingestion rate (half-maximal ingestion within 30 s). This uptake is followed by glycogenolysis associated with an immediate two-fold increase in phosphorylase a activity and a synthase-R to -D conversion within 30 s. Furthermore, in rapid time-course experiments with phagocytozing cells we found that the concentration of cyclic AMP increased by 93% within 15 s and returned to baseline values at 1 min. In a medium without added calcium and with 1 mM ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid, phagocytosis was blocked, cyclic AMP formation decreased by 50% and phosphorylase activation was abolished, but the conversion of synthase-R to -D was preserved. Addition of calcium ions to cells suspended in a calcium-free buffer without added latex results in phosphorylase activation and glycogenolysis, but not in cyclic AMP increase or synthase-R to -D conversion. Measurements of 45Ca efflux during phagocytosis suggest an initial increase in cytosolic calcium obtained by a release of membrane-bound 45Ca. Activation of phosphorylase during phagocytosis is thus presumably due to an increase in cytosol Ca2+ and subsequent activation of phosphorylase kinase, and is independent of the simultaneous increase in concentration of cyclic AMP. Phosphorylation of synthase R to the D form does not depend on the presence of Ca2+ in the extracellular phase.

Effect of metabolites and phosphorylase on the D to I conversion of glycogen synthase from human polymorphonuclear leukocytes

The D to I conversion of glycogen synthase from human polymorphonuclear leukocytes was examined both in a gel-filtered homogenate and in a preparation of glycogen particles with adhering enzymes, purified by chromatography on concanavalin A bound to Sepharose. It was found that glucose 6-phosphate as well as mannose 6-phosphate, glucosamine 6-phosphate, and 2-deoxy-glucose 6-phosphate activated the reaction, whereas the corresponding sugars were without effect. Mn2+ and Ca2+ increased the conversion rate by 51% and 27%, respectively, whereas Mg2+ and inorganic phosphate were without effect. Sodium fluoride inhibited the reaction completely. Glycogen inhibited the reaction in physiological concentrations and 0.5 mM glucose 6-phosphate was able to overcome this inhibition. MgATP greatly augmented the inhibition caused by glycogen in the glycogen particle preparation. This combined effect could be overcome by glucose 6-phosphate in concentrations from 0.1 to 1 mM. Phosphorylase alpha purified from human polymorphonuclear leukocytes inhibited the D to I conversion in a glycogen particle preparation. The inhibition was counteracted by glucose 6-phosphate and to a lesser degree by AMP. Phosphorylase beta was also inhibitory, but only at higher concentrations than phosphorylase alpha. No phosphorylase phosphatase activity was found in the glycogen particle preparation, which may indicate that chromatography on concanavalin A-Sepharose separates this enzyme from the synthase phosphatase or partially destroys the activity of a hypothetical common protein phosphatase.

Changes in serum glucose and lipids, and liver glycogen and phosphorylase during vitellogenesis in nature in the flounder (Platichtys flesus, L.)

1. During vitellogenesis in nature the concentration of phospholipid in serum of female flounders is correlated to the concentration of vitellogenin. 2. High levels of glucose and total lipid in blood occur before the onset of vitellogenesis. During early vitellogenesis the values decrease. At spawning they reach maximum levels. After spawning they decrease to low levels. 3. The concentration of glycogen in the liver oscillates during the period August to May. The phosphorylase activity shows peak activities with high concentrations of glycogen in the liver. There is no simple correlation between glycogen concentration in the liver and glucose concentration in the blood.

Purification and steady state kinetic mechanism of glycogen synthase-D from human polymorpho-nuclear leukocytes

The authors' work on the purification and steady state kinetic investigation of the enzyme glycogen synthase D (UDP-glucose: glycogen 4-alpha-glucosyl-transferase, EC 2.4.1.11) from human polymorphonuclear leukocytes is reviewed. The main features of the kinetic mechanism for catalysis of the reaction interconversion of the quaternary enzyme-substrate-activator complexes. The anions interact exclusively with the G-6-P binding site of the enzyme. The dissociation constants for the enzyme-modifier complexes are determined, and a kinetic mechanism for the action of the anions is proposed, leading to activation or inhibition, depending on the concentration of G-6-P.

Mobilization of granulose in Clostridium pasteurianum. Purification and properties of granulose phosphorylase

1. The granulose of Clostridium pasteurianum ATCC 6013 is degraded when the organism is incubated in a medium containing no utilizable source of carbon and energy. 2. Mobilization of the polyglucan does not occur in the presence of exogenous glucose. 3. Breakdown of granulose is effected by a constitutively synthesized alpha-1,4-polyglucan phosphorylase. 4. Partial (530-fold) purification of this granulose phosphorylase was facilitated by its being loosely bound to the native granules of its substrate polyglucan. 5. The enzyme (pH optimum 6.4) was assayed both (a) in the degradative direction, K(m) for P(i)=2.2mm, and (b) in the synthetic direction, K(m) for glucose 1-phosphate=0.05mm. No requirement for bivalent cations was evidenced. 6. Granulose phosphorylase was inhibited by various nucleotide sugars; GDP-glucose, ADP-glucose (K(i)=20mum) and UDP-glucose (K(i)=60mum) were particularly potent competitive inhibitors. ATP, NADP(+) and NADPH (at 1mm) were less effective inhibitors, whereas AMP was slightly stimulatory. 7. It would appear that granulose mobilization is favoured under conditions of low adenylate energy charge, but is prevented under conditions of ;glucose excess' chiefly by ADP-glucose-mediated inhibition of granulose phosphorylase.