Construction of Glucose-6-Phosphate Dehydrogenase Overexpression Strain of Schizochytrium sp. H016 to Improve Docosahexaenoic Acid Production

Docosahexaenoic acid (DHA) is an important omega-3 polyunsaturated fatty acid (PUFA) that plays a critical physiological role in human health. Schizochytrium sp. is considered an excellent strain for DHA production, but the synthesis of DHA is limited by the availability of nicotinamide adenine dinucleotide phosphate (NADPH). In this study, the endogenous glucose-6-phosphate dehydrogenase (G6PD) gene was overexpressed in Schizochytrium sp. H016. Results demonstrated that G6PD overexpression increased the availability of NADPH, which ultimately altered the fatty acid profile, resulting in a 1.91-fold increase in DHA yield (8.81 g/L) and increased carbon flux by shifting it from carbohydrate and protein synthesis to lipid production. Thus, G6PD played a vital role in primary metabolism. In addition, G6PD significantly increased DHA content and lipid accumulation by 31.47% and 40.29%, respectively. The fed-batch fermentation experiment results showed that DHA production reached 17.01 g/L in the overexpressing G6PD strain. These results elucidated the beneficial effects of NADPH on the synthesis of PUFA in Schizochytrium sp. H016, which may be a potential target for metabolic engineering. Furthermore, this study provides a promising regulatory strategy for the large-scale production of DHA in Schizochytrium sp.

One-time ozone treatment improves the postharvest quality and antioxidant activity of Actinidia arguta fruit

The major aim of this study was to check the effect of one-time ozonation on selected quality parameters and antioxidant status of Actinidia arguta fruit. For this purpose, A. arguta fruit was ozonated with gas at a concentration of 10 and 100 ppm, which was carried out successively for 5, 15 and 30 min. Next, the selected quality attributes, antioxidants level as well as NADPH and mitochondrial energy metabolism in mini-kiwi fruit after ozonation were analysed. Our research has shown that ozonation reduced the level of yeast and mould without affecting the content of soluble solids or acidity. In turn, ozonation clearly influenced the antioxidant activity and the redox status of the fruit. The ozonated fruit was characterised by a lower level of ROS due to the higher level of low molecular weight antioxidants, as well as the higher activity of superoxide dismutase and catalase. In addition, improved quality and antioxidant activity of the fruit were indirectly due to improved energy metabolism and NADPH level. The ozonated fruit showed a higher level of ATP, due to both higher activity of succinate dehydrogenase and higher availability of NADH. Moreover, the increased level of NAD⁺ and the activity of NAD⁺ kinase and glucose-6-phosphate dehydrogenase contributed to higher levels of NADPH in the fruit.

Mitochondrial glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase abrogate p53 induced apoptosis in a yeast model: Possible implications for apoptosis resistance in cancer cells

BACKGROUND

Escape from apoptosis is an important hallmark of tumor progression and drug resistance in cancer cells. It is well demonstrated that over-expression of human wtp53 in Saccharomyces cerevisiae induces apoptosis by directly targeting the mitochondria. In this study, we showed that how S.cerevisiae escaped from p53 induced apoptosis in the presence of a fermentable carbon source (sucrose), but not on non-fermentable carbon source (glycerol).

METHODS

Mitochondrial fractions from yeast cultures grown in the presence of sucrose or glycerol with and without p53 expression were fractionated and analyzed by LC-MS/MS. Differentially expressed proteins were studied and detailed biochemical analysis for selected proteins was performed.The effect of mitochondrial HXK-2 over-expression induced by p53 in sucrose grown cells on cell survival was evaluated using gene deletion/tagging, co-localisation and mitochondrial ROS detection.

RESULTS

We observe that mitochondria isolated from p53 over-expressing cells accumulate Pentose phosphate Pathway (PPP) enzymes including glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) which led to enhanced mitochondrial NADPH production only when cells are cultured in sucrose but not glycerol. In contrast, mitochondria isolated from Δhxk2 p53 over-expressing cells grown in sucrose did not accumulate G6PDH and 6PGDH and resulted in defective growth.

CONCLUSIONS

Enhanced association of HXK2 with the mitochondria with the concomitant accumulation of G6PDG and 6PGDH results in increased NADPH that scavenges ROS and provides resistance to apoptosis.

GENERAL SIGNIFICANCE

Given the extensive similarity of aerobic glycolysis between humans and yeast, the phenomena described here could as well be responsible for the escape of apoptosis in cancer cells.

The effect of Zn2+ on glucose 6-phosphate dehydrogenase activity from Bufo arenarum toad ovary and alfalfa plants

The effect of Zn2+ on glucose 6-phosphate dehydrogenase (G6PD) activity was monitored in samples from Bufo arenarum toad ovary and alfalfa plants, in the search for a possible new bioindicator able to detect levels of exposure through contaminated soils, and also to elucidate possible similarities between the enzyme from animal and plant tissues. The in vivo effect was evaluated after exposure of the toads to the metal in Ringer solution during 30 days and after 10 days of treatment in 6 weeks old plants, cultured under laboratory conditions. In vitro effects were measured in different extracts from control samples and partially purified enzyme from ovarian tissue as well as in different extracts from control alfalfa plants, by addition of the metal to the reaction mixture containing the enzyme. G6PD from toad ovary was noncompetitively inhibited by zinc both in vivo and in vitro, under all the experimental conditions studied. A kinetic analysis of the enzyme activity showed that the Michaelis-Menten constant (Km) was not modified, while maximal velocity (Vmax) decreased as the consequence of treatment. It was not possible to obtain a dose-response curve for the effects of Zn2+ on G6PD from alfalfa whole plants, measured in vivo or in vitro. Only leaf extracts evidenced a possible relationship between treatment with the metal and G6PD activity alteration. The results agree with a possible role for G6PD as a biomarker of effect and exposure to Zn2+ in B. arenarum ovarian tissue but not in alfalfa plants.

Effects of long-term exposure to Cu2+ and Cd2+ on the pentose phosphate pathway dehydrogenase activities in the ovary of adult Bufo arenarum: possible role as biomarker for Cu2+ toxicity

The effects of copper and cadmium on metabolism through the pentose phosphate pathway were evaluated in Bufo arenarum toad ovary. The effects of the two metals on dehydrogenases from this pathway were evaluated by three experiments: (1) in samples obtained from control females with addition of the metals to the reaction mixture (in vitro), (2) in samples obtained from control females and after long-term exposure of females to 4 and 100 microg/L of Cu or Cd in the incubation media (in vitro after exposure to the metals in vivo), and (3) 14CO2 production through the pentose phosphate pathway was evaluated after [U-14C]glucose microinjection on ovulated oocytes (in vivo after microinjection of the metals). Results from (1) evidenced inhibition of both enzyme activities but only above 1.5 mM Cu and Cd added to the reaction mixture. In (2) both glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities decreased in samples from the ovaries of females exposed in vivo to Cu, in a concentration-dependent manner (up to 90% in females exposed to 100 microg/L Cu: 2.12 +/- 1.57 NADPH micromol/min microg protein x 10(-5) vs 19.97 +/- 8.54 in control females). Cd treatment of the toads only rendered an inhibitory effect on 6-phosphogluconate dehydrogenase activity after exposure to 4 microg/L of the bivalent cation. (3) In vivo 14CO2 evolution significantly decreased in oocytes coinjected with 6.3 x 10(-3) mM Cu (calculated intracellular final concentration of the metal injected) and radioactive glucose. Cu and Cd concentration in samples from exposed females were always under detection limit by particle-induced X-ray emission. The results presented here are in agreement with a role for both glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities determination as biomarkers of effect and exposure for Cu but not for Cd toxicity.

Effect of sulfur dioxide inhalation on the glutathione redox system in mice and protective role of sea buckthorn seed oil

This study investigated the effects of sulfur dioxide (SO2) inhalation and protection by sea buckthorn seed oil from oxidative damage caused by SO2 in male Kunming-strain mice. One approach was set up to study the effects of SO2 inhalation on changes of the mice antioxidant defense system. SO2 at different concentrations (22 +/- 2, 64 +/- 3, and 148 +/- 23 mg/m3) was administered to animals in treatment groups for 7 days, 6 h per day, while control groups were exposed to filtered air under the same condition. The activities of glutathione-S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PD) and the contents of reduced glutathione (GSH) in brain, lung, heart, liver, and kidney of mice were measured. In the case of inhalation of a SO2 concentration of 148 +/- 23 mg/m3, the activities of GST and G6PD and contents of GSH in the brain, lung, heart, liver, and kidney were significantly decreased. Dose-dependent relations were found between various SO2-exposed concentrations and the activities of GST and G6PD and the content of GSH. Meanwhile another approach was taken to determine whether sea buckthorn seed oil could maintain the glutathione redox system and prevent the oxidative damage of lung induced by SO2. In groups given a high dosage (6 or 8 ml/kg) intraperitoneally, the level of TBARS (thiobarbituric acid-reactive substances) was decreased significantly (p < 0.05) by the injection of sea buckthorn seed oil, and the activity of GST was increased significantly (p < 0.05). Overall GST activity and TBARS level exhibited a significant negative correlation (r = 0.891, p < 0.05). The observations showed that SO2 inhalation resulted in a significant change in the glutathione redox system and indicated that sea buckthorn seed oil could contribute to the antioxidant effects in the case of SO2 exposure.

Effects of phenylhydrazine or recombinant human erythropoietin on deformability and activity of dehydrogenase glucose-6-phosphate and acetylcholinesterase in Wistar rats blood enriched in reticulocytes

Deformability and activity of the enzymes: acetylcholinesterase (AChE) and dehydrogenase glucose-6-phosphate (G-6-PD), were assayed for RBC enriched in immature reticulocytes. Reticulocytosis was evoked by administration of two different drugs: recombinant human erythropoietin (rHuEPO) and phenylhydrazine (PHZ) to two groups of Wistar rats. After treatment with the former compound, a group of animals exhibited 17.33% reticulocytes in blood whereas a group of rats treated with the latter drug reached 57.66% of these cells in blood. A marked decrease in RBC deformability was found in both groups of animals. AChE did not significantly change activity neither in PHZ-treated nor in rHuEPO-treated rats, whereas G-6-PD activity was significantly decreased in the PHZ-treated group.

Effects of aluminum on physiological metabolism and antioxidant system of wheat (Triticum aestivum L.)

The Al-tolerant cultivar TAM202 and the Al-sensitive cultivar TAM 105 of winter wheat (Triticum aestivum L.) were exposed to 0, 50, 75, 100 or 150 microM of Al. The absorption of Al by wheat, the growth of root, several key enzymes concerned with C, N and P metabolism, as well as key constituents of antioxidant system, were investigated. The results showed that TAM105 absorbed more Al than TAM202 and its root growth (presented by the length) was inhibited more severely. The root growth was most closely related to mononuclear Al (Ala) activity. The metabolic enzymes (presented by glucose-6-phosphate dehydrogenase, nitrate reductase and acid phosphatase) in TAM202 were Al-tolerant. Presented by superoxide dimutase (SOD) and the content of reduced glutathione (GSH) and malondialdehyde (MDA), antioxidant system in TAM202 indicated lower oxidative stress and greater ability to protect the cultivar.

Some factors affecting mutant numbers in the Salmonella/microsome assay

An examination has been made of some of the parameters which can affect mutant numbers in the Salmonella/microsome assay. The type of minimal media plates used for the assay and the concentration of glucose-6-phosphate, one of the co-factors necessary for mono-oxygenase action, had no effect on mutant numbers. Increases in mutated bacteria resulted from the use of (1) log-phase bacteria, (2) higher NADP concentrations than those normally recommended, and (3) higher phosphate buffer concentrations. Six mutagens, i.e., 2-acetylaminofluorene (AAF), 3,3'-dichlorobenzidine (3,3'-DCB), cyclophosphamide (CY), aflatoxin B1 (AFB1), 3-methylcholanthrene (3MC) and benzo[a]pyrene (BP), all requiring mono-oxygenase activation, were studied with two Salmonella typhimurium strains, TA98 and TA100, and liver preparations from rats given different inducing agent treatments using optimum conditions. Phenobarbitone induction was generally superior to Aroclor-1254 in converting these substrates to mutagens except for the polycyclic hydrocarbon substrates. A comparison of 3-methylcholanthrene, Aroclor-1254, beta-naphthoflavone or phenobarbitone as inducing agents revealed the first three of these to be equally effective in activating BP or 3MC to mutagens, whereas phenobarbitone was less active. Dual administration of 3-methylcholanthrene and phenobarbitone to rats did not result in an additive mutagenic effect using AAF, AFB1 or 3,3'-DCB as substrates, the numbers of mutant bacteria obtained being only equal to that seen with 3-methylcholanthrene alone. These differences were not due to there being different liver protein optima for the various inducing agent treatments. The foregoing results are discussed in relation to attempts to draw up a rigid protocol for mutagenicity testing.

Sample pretreatment with nitrate reductase and glucose-6-phosphate dehydrogenase quantitatively reduces nitrate while avoiding interference by NADP+ when the Griess reaction is used to assay for nitrite

An assay for the simultaneous measurement of nitrite and nitrate, products of nitric oxide metabolism, is described. Others have reported pretreating sample by using nitrate reductase (NR) and NADPH to reduce endogenous NO3- before assaying the resultant NO2- using the Griess reaction. However, we found that the NADP+ formed during pretreatment interfered with the Griess reaction when NADPH was used at concentrations necessary to drive the NR reaction. For instance, 500 microM NADP+ in 100 microM NaNO3- (without NR) causes a 90% interference with the formation of Griess reaction product. To limit interference, we modified the method by decreasing the NADPH concentration to 1 microM. NADPH was regenerated by coupling the NR reaction with that catalyzed by glucose-6-phosphate dehydrogenase (GD). Using this method, NaNO3- standard curves were linear up to 100 microM and coincided with control curves obtained using NaNO2- incubated in parallel. Addition of urine up to a strength of 20% did not interfere with the assay. Comparison with an alternative assay based on cadmium reduction resulted in the following linear regression: [Cd method] = 0.915*[NR-GD method] + 0.37, r2 = 0.997. Coupling GD to NR to recycle NADPH allows this cofactor to be used at a low concentration so that interference with the Griess reaction is negligible.

Biochemical mechanisms of hydrogen peroxide- and hypochlorous acid-mediated inhibition of human mononuclear leukocyte functions in vitro: protection and reversal by anti-oxidants

Both H2O2 (IC50 = 70 microM) and HOCl (IC50 = 8.5 microM) inhibited mitogen-induced MNL proliferation in a dose-dependent manner. This was found to be due to a depletion of intracellular ATP by at least two distinct mechanisms. HOCl and high concentrations (greater than 100 microM) of H2O2 inhibit ATP generation via sulfhydryl group oxidation on the active site of the glyceraldehyde-3-phosphate dehydrogenase (G3PDH) enzyme of the glycolytic pathway. On the other hand, low H2O2 concentrations cause ATP depletion by an activation of the DNA repair enzyme, poly(ADP-ribose)polymerase (pADPRP), leading to consumption of NAD+, an essential cofactor for G3PDH. The anti-oxidants ascorbate and cysteine protected MNL against the anti-proliferative effects of HOCl. Similar results were achieved with the HOCl-mediated inhibition of ATP production and G3PDH activity. However, ascorbate was unable to protect against H2O2-mediated inhibition of MNL functions, while cysteine protected against the inhibitory effects on ATP production and G3PDH activity, induced by this oxidant.

[The role of gonadotropins, cyclic AMP, 22-R-hydroxycholesterol and cofactors in regulating endocrine functions of the Leydig cells in rats. I. Effect of cofactors on the synthesis of steroid hormones in the interstitial gland of rats]

The authors evaluated the influence of NAD, NADP, G-6-P and G-6-PDH on the synthesis of steroid hormones in the interstitial gland of the rat. The animals were killed by decapitation, and sections of the nucleus weighing altogether 20 mg were incubated with NAD (0.4 mM), NADP (0.4 mM), G-6-P (3.5 mM) and G-6-PDH (2 j.m./ml) for 4 hours in CO2 incubator. Then the tissue was homogenized, removed by centrifugation and then from the homogenous supernatant the authors extracted steroids which were in the incubating medium and in the tissue. Steroid hormones examined were marked radioimmunologically, they were: pregnenolon as the first and testosterone as the second stage of synthesis of nucleus androgens. The search carried out shows that the strongest stimulator in biosynthesis of pregnenolon was NADP together with the reducing system (G-6-P and G-6-PDH). On the other hand, in case of testosterone the highest effectiveness was achieved by simultaneous use of the cofactors examined. Applying cofactors separately the authors were able to find that both NAD and NADP together with the reducing system were responsible for testosterone synthesis and their simultaneous applying in the incubating medium leads to a synergistic effect.

[The role of gonadotropins, cyclic AMP, 22-R-OH-cholesterol and cofactors in regulating endocrine functions of the Leydig cells in rats. III. Mechanisms responsible for "desensitization" of the Leydig cells of rats caused by high doses of hCG]

Two groups of rats (a control group and the group examined) were administered intraperitoneally supraphysiological doses of hCG in order to induce a "down regulation" effect on the level of receptors LH and to achieve the desensibilization of Leydig cells. The authors tried to find out at which stage of sequence of changes from receptor stimulation to hormone production there appears a state of cellular resistance to further stimulation. Sections of the nucleus were incubated with various substances influencing steridogenesis (LH, hCG, dbcAMP, 22-R-OH-cholesterol, NAD + NADP + G-6-P + G-6-PDH). An index of the influence of the above substances on the synthesis of androgens were amounts of pregnenolon as the first and testosterone as the final stage of hormonal changes marked radioimmunologically in nucleus homogenates and incubating media. It was shown that the resistance of Leydig cells to further stimulation in the group of animals that were given high doses of hCG is the result of enzymatic blocks in testosterone synthesis. The first block is "late" block of 17 alpha-hydroxylase and 17-20 desmolase, disturbing transforming of 21-carbon steriods into 19-carbon androgens. When the dose of hCG increases, there appears the second block, the so called "early" block, disturbing mitochondrial synthesis of pregnenolon. It was found that exogenic cofactors are in a position, at least partially, to restore the activity of blocked enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

[The role of gonadotropins, cyclic AMP, 22-R-hydroxycholesterol and cofactors in regulating endocrine functions of the Leydig cells in rats. II. Effects of LH, hCG, dbcAMP, 22-R-OH-cholesterol and cofactors on the synthesis of pregnenolone and testosterone in the interstitial gland of rats]

The authors examined in vitro the influence of gonadotrophins, cAMP, 22-R-OH-cholesterol and cofactors on the synthesis of pregnenolon and testosterone in the interstitial gland of the rat. Sections of the nucleus were incubated with LH (100 ng/ml), hCG (1.0 j.m./ml), dbcAMP (1 mM), 22-R-OH-cholesterol (30 microM) and cofactors (NAD + NADP + G-6-P + G-6-PDH). It was found that an increase in concentrations of hCG above physiological values was not accompanied by an increase in secreting steroid hormones. LH, hCG and dbcAMP increased the synthesis of pregnenolon twice, and testosterone--three times. 22-R-OH-cholesterol as a substrate increased the synthesis three and four times respectively, and added cofactors five times and four and a half times respectively. Joining 22-R-OH-cholesterol or a cofactor with LH does not intensify a stimulating effect.

Mutagenic activation of carcinogenic N-nitrosopropylamines by rat liver: evidence for a cytochrome P-450 dependent reaction

Mutagenic potential of carcinogenic N-nitrosopropylamines was examined by the Ames's liquid incubation assay, using rat liver 9000 g supernatant (S9) fraction for metabolic activation. N-Nitrosobis(2-hydroxypropyl)amine, N-nitroso(2-hydroxypropyl)-(2-oxopropyl)amine (HPOP), N-nitrosobis(2-oxopropyl)amine (BOP), N-nitrosobis(2-acetoxypropyl)amine, N-nitroso-2,6-dimethylmorpholine, N-nitrosomethyl-(2-hydroxypropyl)amine and N-nitrosomethyl(2-oxopropyl)amine all showed positive mutagenicity in strain TA100 in the presence of liver S9 while being negative in strain TA98. With the exception of HPOP and BOP, which were also mutagenic in TA100 without S9 metabolic activation, these N-nitrosopropylamines required the presence of microsomes as a source of enzymes as well as NADP+ as a cofactor for mutagenic activation. Treatment of rats with polychlorinated biphenyls or phenobarbital (PB) resulted in a marked increase in the ability of S9 to activate the seven N-nitrosamines tested whereas 3-methylcholanthrene (3-MC) induction was not effective. All the mutagenic activities were considerably decreased by preincubation in an atmosphere of either carbon monoxide or nitrogen gas or by adding cytochrome c to the S9 mixture. Metyrapone, a specific inhibitor of PB-inducible major cytochrome P-450, considerably inhibited mutagenicity, whereas 7,8-benzoflavone, a specific inhibitor of 3-MC-inducible major cytochrome P-448, was totally lacking this effect. These results demonstrate a correlation between rat liver S9 dependent mutagenicity of six N-nitrosopropylamines and their known carcinogenicity in rat in vivo experiments, and that the PB-inducible major cytochrome P-450 is involved in the mutagenic activation. BOP was also shown to be activated by extrahepatic (lung, kidney, pancreas) tissue S9, blood S9 and bovine serum albumin (BSA) to the extent of 50% of that activity obtained with liver S9. A possible mechanism of BSA-mediated activation of BOP is discussed.

Glycogen synthase activity in Chinese hamster ovary cells. Studies with wild-type and mutant cells defective in cyclic AMP-dependent protein kinase

Glycogen synthase (EC 2.4.1.11) activity was studied in cell extracts from wild-type Chinese hamster ovary (CHO) cells and three mutants resistant to cyclic AMP effects on cell shape and cell growth. Based on the capacity of crude extracts to phosphorylate exogenous histone, two of the mutants appeared to have altered cyclic AMP-dependent protein kinase (EC 2.7.1.37) and one of them had apparently normal amounts of kinase activity. Glycogen synthase activity was present in comparable amounts in wild-type and all three mutant strains in a presumably inactive phosphorylated form since activity was virtually completely dependent upon the presence of glucose 6-phosphate. The enzyme could be partially dephosphorylated by endogenous phosphatases and rephosphorylated by exogenous cyclic AMP-dependent protein kinase. Attempts to find culture conditions (e.g. glucose starvation) or cell treatment (e.g. insulin) which might activate glycogen synthase in intact cells were unsuccessful. since glycogen synthase activity present in CHO cells was independent of the level of cyclic AMP-dependent kinase, we conclude that cyclic AMP-dependent protein kinase does not play a critical role in regulating the state of phosphorylation of the synthase.

An investigation of factors influencing the measurement of creatine phosphokinase activity in serum using coupled enzymatic methods

1. The factors influencing the measurement of creatine phosphokinase (CPK) activity in serum by coupled enzymatic methods were investigated to establish optimum conditions for this type of assay. Such a study was indicated following observations by the authors of poor performance of commerically produced reagent kits together with the failure of most of the established an well accepted methods to operate under true optimum zero order kinetics in the reaction phase state. 2. The factors invested were the effects of pH, substrate concentrations (creatine phosphate, glucose and NADP+), added auxiliary (hexokinase) and indicator (glucose-6-phosphate dehydrogenase) enzymes, dithiothreitol (DTT) as an activator and conditions of storage of substrate stability. DTT was found to be a suitable activator but not a reactivator of the reaction. The optimum concentrations of creatine phosphate, glucose and NADP+ were found to be 20.0, 20.0 and 2.0 mmol/litre, respectively. Optimum activieies of the enzymes, glucose-6-phosphate dehydrosenase and hexokinase were 1000 and 2000 units/litre, respectively. 3. The between-day precision of the method for measuring serum at pH 6.8 and 30 degrees C at three activity levels under the optimum conditions developed was excellent yielding coefficients of variation ranging from 2.0 to 2.7%.

Incorporation of N-acetylglucosamine into endogenous acceptors of rough microsomes from rat liver: stimulation by GTP after treatment with pyrophosphate

Upon incubation of UDP-N-acetyl[14C]glucosamine and GDP-mannose with rough microsomes from rat liver, GlcNAc incorporation occurred mostly into acid-labile products extractable by chloroform/methanol that were presumed to be dolichol pyrophosphate GlcNAc and, for a small part, dolichol pyrophosphate N,N'-diacetylchitobiose. The production of this latter glycolipid was greatly enhanced when rough microsomes, previously treated with pyrophosphate, were incubated in the presence of GTP. Furthermore, under these particular conditions, high levels of radioactivity were obtained in products precipitated by trichloroacetic acid and not extracted by chloroform/methanol. The label appeared in acid-labile and in acid-resistant products, presumed to be dolichol pyrophosphate mannosylated oligosaccharides, and glycoproteins, respectively. From these results, dolichol pyrophosphate N,N'-diacetylchitobiose appears to be an obligate metabolic intermediate in protein glycosylation by this system. Whether or not dolichol pyrophosphate N,N'-diacetylchitobiose must be mannosylated prior to transfer of the N,N'-diacetylchitobiose moiety to protein is an open matter, because GlcNAc was also incorporated into acid-resistant products when the reaction was carried out in absence of GDP-mannose.

[Effect of ACTH on glucose-6-phosphate dehydrogenase and transketolase activity in mitochondria and hyaloplasm of rabbit liver]

The glucose-6-phosphate dehydrogenase and transketolase activities in mitochondria and hyaloplasm of the rabbit liver were studied as affected by ACTH injected daily in a dose of 10 u/kg of weight for two weeks. It was shown that the activity of glucose-6-phosphate dehydrogenase was unchanged neither in mitochondria nor in hyaloplasm. The transketolase activity in hyaloplasm was not changed as well. But in mitochondria it decreases by 47% (by an increase of sedoheptulose-7-phosphate S-7-P) simultaneously the ribose-5-phosphate (R-5-P) conversion is inhibited by 35%. The ratio of converted R-5-P and formed S-7-P became 2:0.68 (instead of theoretical 2:1). Administration of ACTH has no effect on the total concentration of acid-soluble ribose-containing compounds in both mitochondria and hyaloplasm.

An interstrain difference in cholesterol synthesis in vitro in mice, dependent upon a difference in endogenous NADPH-generating capacity

Earlier experiments have shown that significantly more endogenously generated NADPH is available for reduction of corticosterone in liver homogenates from C57BL/10 male mice than in those from the DBA/2 strain. To test the effect of this interstrain difference upon a representative NADPH-requiring biosynthetic pathway in vitro, the biosynthesis of cholesterol from mevalonic acid was studied in homogenates of livers from the two strains of mice, with and without addition of an NADPH-generating system. The incorporation of mevalonic acid into cholesterol in homogenates from the C57BL/10 strain is little affected by omission of the NADPH-generating system, but in the DBA/2 strain, addition of an NADPH-generating system is necessary to elevate the level of cholesterol synthesis to that of the C57BL/10 strain. Without this addition, the DBA/2 homogenate mainly produces lanosterol and other precursors of cholesterol which require NADPH for their further metabolism.

The effect of progesterone, glucose-6-phosphate dehydrogenase, adrenocorticotrophic hormone and metyrapone on adrenocortical secretion of rat adrenal glands cultured under hyperbaric oxygen

Exposure of organ cultures of rat adrenal glands to hyperbaric oxygen at 2 atm. increases steroid output during the first 24 hr. but the secretion rate falls after that time. This reduction is partially prevented by the addition of progesterone and during the period 24–48 hr. completely prevented by the addition of progesterone together with glucose-6-phosphate, glucose-6-phosphate dehydrogenase and nicotinamide adenine dinucleotide phosphate.

Addition of bovine and synthetic adrenocorticotrophin to cultures maintained in hyperbaric oxygen results in a further increase in steroid secretion during the period 0–6 hr. Addition of metyrapone results in a reduction in the output of corticosterone, 18-hydroxycorticosterone and aldosterone.

Control of glycolysis in cerebral cortex slices

1. Intracellular concentrations of intermediates and cofactors of glycolysis were measured in guinea-pig cerebral cortex slices incubated under varying conditions. 2. Comparison of mass-action ratios with apparent equilibrium constants for the reactions of glycolysis showed that hexokinase, phosphofructokinase and pyruvate kinase catalyse reactions generally far from equilibrium, whereas phosphoglucose isomerase, aldolase, phosphoglycerate kinase, phosphoglycerate mutase, enolase, adenlyate kinase and creatine phosphokinase are generally close to equilibrium. The possibility that glyceraldehyde 3-phosphate dehydrogenase may catalyse a ;non-equilibrium' reaction is discussed. 3. Correlation of changes in concentrations of substrates for enzymes catalysing ;non-equilibrium' reactions with changes in rates of glycolysis caused by alteration of the conditions of incubation showed that hexokinase, phosphofructokinase, pyruvate kinase and possibly glyceraldehyde 3-phosphate dehydrogenase are subject to metabolic control in cerebral cortex slices. 4. It is suggested that the glycolysis is controlled by two regulatory systems, the hexokinase-phosphofructokinase system and the glyceraldehyde 3-phosphate dehydrogenase-pyruvate kinase system. These are discussed. 5. It is concluded that the rate of glycolysis in guinea-pig cerebral cortex slices is limited either by the rate of glucose entry into the slices or by the hexokinase-phosphofructokinase system. 6. It is concluded that addition of 0.1mm-ouabain to guinea-pig cerebral cortex slices causes inhibition of either glyceraldehyde 3-phosphate dehydrogenase or phosphoglycerate kinase or both, in a manner independent of the known action of ouabain on the sodium- and potassium-activated adenosine triphosphatase.