The metabolism of glucose by heterocysts and vegetative cells of Anabaena cylindrica

Whole filaments of autotrophically grown Anabaena cylindrica and heterocysts isolated from them will assimilate and metabolise exogenous glucose. Radiorespirometric experiments suggest the operation of the pentose phosphate pathway. Glucose-6-phosphate and 6-phosphogluconate dehydrogenase are present in heterocysts at 6–8 times the levels found in vegetative cells whereas enzymes of the reductive pentose phosphate and glycolytic pathways are barely or not detectable. Glucose-6-phosphate dehydrogenase in vegetative cells, but not in heterocysts is subject to inhibition by ribulose diphosphate.     

Changes in activity of enzymes metabolizing glucose 6-phosphate during development of the basidiomycete Schizophyllum

During the formation of fruit bodies in the basidiomycete Schizophyllum commune, there are changes in the specific activities of the enzymes utilizing glucose 6-phosphate. These include a 50% increase in the relative amount of glucose-6-phosphate dehydrogenase followed by a decrease in this enzyme and a 90% decrease in phosphoglucomutase activity. This results in a 10-fold change in the relationship between these two enzymes during development. The activities in several mutants were examined and abnormal enzyme levels were found in some cases. The activity of 6-phosphogluconate dehydrogenase was also examined, and its contribution to the assay of the other enzymes was determined.     

The control properties of phosphofructokinase in relation to the respiratory climacteric in banana fruit

Glucose 6-phosphate, fructose 6-phosphate, fructose 1, 6-diphosphate, and triose phosphates, and the enzymes phosphofructokinase, aldolase, and glucose 6-phosphate dehydrogenase were extracted from banana fruit (Musa cavendishii, Lambert var. Valery) at the (a) preclimacteric, (b) climacteric rise, (c) climacteric peak, and (d) postclimacteric stages of ripening. The level of fructose 1, 6-diphosphate increased 20-fold whereas the concentration of other intermediates changed no more than 2.5-fold between stages a and c. For these same extracts, phosphofructokinase activity increased 2.5-fold whereas the activity of glucose 6-phosphate dehydrogenase and aldolase changed only fractionally. Substrate saturation studies (fructose 6-phosphate) of phosphofructokinase activity showed a decrease in the [S]_0.5 from 5.6 to 1.7 mM betwen stages a and c. The enzyme from both sources seems to be regulated by a negative cooperative effect with the control being more stringent in the enzyme from stage a. The difference in enzyme activity is consistent with the increase in respiratory activity between the two stages.     

Enzymes of glucose metabolism in normal mouse pancreatic islets

1. Glucose-phosphorylating and glucose 6-phosphatase activities, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, NADP⁺-linked isocitrate dehydrogenase, `malic' enzyme and pyruvate carboxylase were assayed in homogenates of normal mouse islets. 2. Two glucose-phosphorylating activities were detected; the major activity had K<sub>m</sub> 0.075mm for glucose and was inhibited by glucose 6-phosphate (non-competitive with glucose) and mannoheptulose (competitive with glucose). The other (minor) activity had a high K<sub>m</sub> for glucose (mean value 16mm) and was apparently not inhibited by glucose 6-phosphate. 3. Glucose 6-phosphatase activity was present in amounts comparable with the total glucose-phosphorylating activity, with K<sub>m</sub> 1mm for glucose 6-phosphate. Glucose was an inhibitor and the inhibition showed mixed kinetics. No inhibition of glucose 6-phosphate hydrolysis was observed with mannose, citrate or tolbutamide. The inhibition by glucose was not reversed by mannoheptulose. 4. 6-Phosphogluconate dehydrogenase had K<sub>m</sub> values of 2.5 and 21μm for NADP<sup>+</sup> and 6-phosphogluconate respectively. 5. Glucose 6-phosphate dehydrogenase had K<sub>m</sub> values of 4 and 22μm for NADP<sup>+</sup> and glucose 6-phosphate. The K<sub>m</sub> for glucose 6-phosphate was considerably below the intra-islet concentration of glucose 6-phosphate at physiological extracellular glucose concentrations. The enzyme had no apparent requirement for cations. Of a number of possible modifiers of glucose 6-phosphate dehydrogenase, only NADPH was inhibitory. The inhibition by NADPH was competitive with NADP<sup>+</sup> and apparently mixed with respect to glucose 6-phosphate. 6. NADP<sup>+</sup>–isocitrate dehydrogenase was present but the islet homogenate contained little, if any, `malic' enzyme. The presence of pyruvate carboxylase was also demonstrated. 7. The results obtained are discussed with reference to glucose phosphorylation and glucose 6-phosphate oxidation in the intact mouse islet, and the possible nature of the β-cell glucoreceptor mechanism.     

Regulation of liver and brain hexose monophosphate dehydrogenases by insulin and dietary intake in the female rat

Summary Liver glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities were significantly decreased in both diabetic and fasted rats. Treatment of diabetic rats with insulin resulted in liver glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities that were significantly greater than controls. Insulin promoted an increase in food consumption that was blocked by adrenaline. Insulin, when administered together with adrenaline, restored hepatic glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenas activities of diabetic animals to control values, without altering food consumption. Brain glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities were not significantly altered by either dietary restriction, diabetes or insulin treatment. These results demonstrate a dissociation between the action of insulin on hepatic glucose 6-phosphate dehydrogenase activity and its action to increase food intake.Abbreviations NADP⁺ oxidoreductase, EC 1.1.1.49 Glucose 6-P dehydrogenase, GPD, D-glucose-6-phosphate - NADP⁺ 2-oxidoreductase (decarboxylating), EC 1.1.1.44 phosphogluconate dehydrogenase, PGD, 6-phospho-D-gluconate     

Decrease of Glucose 6-Phosphate and 6-Phosphogluconate Dehydrogenase Activities in the Xylem of Populus gelrica on Budding

The activities of glucose 6-phosphate and 6-phosphogluconate dehydrogenases, transketolase, phosphoglucose isomerase, and fructose 6-phosphate kinase were studied in extracts of wintering poplar (Populus gelrica) xylem. The xylem of wintering poplar showed high levels of transketolase, glucose 6-phosphate, and 6-phosphogluconate dehydrogenases. On recommencement of growth, the two dehydrogenase activities decreased. The three remaining enzymes appeared to be unchanged. In spring and early summer, glucose 6-phosphate dehydrogenase of the xylem was extremely low. On the other hand, 6-phosphogluconate dehydrogenase, which also became lower during the metabolic shift from winter to spring, was readily detected, and was several times higher than glucose 6-phosphate dehydrogenase throughout the year. The low dehydrogenase activities lasted into late October and then appeared to resume their original activity. A shift of metabolism at the beginning of growth was also observed by measuring the amount of sugar phosphates, soluble amino acids and amides, and proteins in the xylem. In contrast to the decrease of the two dehydrogenases and soluble proteins at the time of budding, incorporation of lysine-U-¹⁴C into the xylem protein ramained constant. A method to transfuse radioactive compounds into a section of stem was described.     

Fructose supports glycogen accumulation,heterocysts differentiation,N2 fixation and growth of the isolated cyanobiont Anabaena azollae

Cells of the cyanobiont Anabaena azollae isolated from the water fern Azolla filiculoides were found to take up and utilize fructose in the light for mixotrophic growth. Fructose was favored by the cyanobiont as a substrate over sucrose and glucose. Cell growth in the presence of 8 mM fructose led to glycogen accumulation in the cells which approached 20% of the cell dry weight within 2 to 3 days, followed by reduction of glycogen content during the fourth day. Glucose-6-phosphate dehydrogenase activity was increased 5–6-fold in the fructose grown cells from the third day of growth onwards. The frequency of heterocysts in fructose-grown cells increased from 6 to 18%, and acetylene reduction by nitrogenase was increased 3-fold in the presence of fructose as compared with control cells, with maximum values observed between the third and fifth day of mixotrophic growth. Fructose-supported growth yielded a 2–4-fold increase in cell dry weight over controls.It is suggested that fructose-supported development and growth of the cyanobiont in batch cultures may resemble its mixotrophic growth and development in situ in the leaf cavity of the host fern Azolla.Abbreviation G6PDH glucose-6-phosphate dehydrogenase     

The pentose phosphate pathway of glucose metabolism. Hormonal and dietary control of the oxidative and non-oxidative reactions of the cycle in liver

1. Measurements were made of the non-oxidative reactions of the pentose phosphate cycle in liver (transketolase, transaldolase, ribulose 5-phosphate epimerase and ribose 5-phosphate isomerase activities) in a variety of hormonal and nutritional conditions. In addition, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities were measured for comparison with the oxidative reactions of the cycle; hexokinase, glucokinase and phosphoglucose isomerase activities were also included. Starvation for 2 days caused significant lowering of activity of all the enzymes of the pentose phosphate cycle based on activity in the whole liver. Re-feeding with a high-carbohydrate diet restored all the enzyme activities to the range of the control values with the exception of that of glucose 6-phosphate dehydrogenase, which showed the well-known ;overshoot' effect. Re-feeding with a high-fat diet also restored the activities of all the enzymes of the pentose phosphate cycle and of hexokinase; glucokinase activity alone remained unchanged. Expressed as units/g. of liver or units/mg. of protein hexokinase, glucose 6-phosphate dehydrogenase, transketolase and pentose phosphate isomerase activities were unchanged by starvation; both 6-phosphogluconate dehydrogenase and ribulose 5-phosphate epimerase activities decreased faster than the liver weight or protein content. 2. Alloxan-diabetes resulted in a decrease of approx. 30-40% in the activities of 6-phosphogluconate dehydrogenase, ribose 5-phosphate isomerase, ribulose 5-phosphate epimerase and transketolase; in contrast with this glucose 6-phosphate dehydrogenase, transaldolase and phosphoglucose isomerase activities were unchanged. Treatment of alloxan-diabetic rats with protamine-zinc-insulin for 3 days caused a very marked increase to above normal levels of activity in all the enzymes of the pentose phosphate pathway except ribulose 5-phosphate epimerase, which was restored to the control value. Hexokinase activity was also raised by this treatment. After 7 days treatment of alloxan-diabetic rats with protamine-zinc-insulin the enzyme activities returned towards the control values. 3. In adrenalectomized rats the two most important changes were the rise in hexokinase activity and the fall in transketolase activity; in addition, ribulose 5-phosphate epimerase activity was also decreased. These effects were reversed by cortisone treatment. In addition, in cortisone-treated adrenalectomized rats glucokinase activity was significantly lower than the control value. 4. In thyroidectomized rats both ribose 5-phosphate isomerase and transketolase activities were decreased; in contrast with this transaldolase activity did not change significantly. Hypophysectomy caused a 50% fall in transketolase activity that was partially reversed by treatment with thyroxine and almost fully reversed by treatment with growth hormone for 8 days. 5. The results are discussed in relation to the hormonal control of the non-oxidative reactions of the pentose phosphate cycle, the marked changes in transketolase activity being particularly outstanding.     

Catalases protect cellular proteins from oxidative modification in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae cells had higher antioxidant enzyme activities under growth in ethanol than that in glucose as a carbon and energy source. The correlations between catalase activity and protein carbonyl level (r(2)=0.857), between catalase and glucose-6-phosphate dehydrogenase activities (r(2)=0.924) and between protein carbonyl levels and glucose-6-phosphate dehydrogenase activity (r(2)=0.988) under growth in ethanol were found. Growing in ethanol the strain deficient in cytosolic and peroxisomal catalases had 7.1-fold higher level of carbonyl proteins than that of wild-type strain. Our data suggest that in vivo catalases may protect glucose-6-phosphate dehydrogenase against oxidative inactivation.     

Regulation of Chloroplast Development by Nitrogen Source and Growth Conditions in a Chlorella protothecoides Strain

Chlorella strain (UTEX 27) maintains optimal photosynthetic capacity when growing photoautotrophically in the presence of ammonium. Nitrate-grown photoautotrophic cells, however, show a drastic loss of chlorophyll content and ribulose-1,6-bisphosphate carboxylase/oxygenase activity, resulting in a greater than 10-fold decrease in photosynthetic capacity and growth rate. Nitrate-grown cells are not deficient in protein content, and under mixotrophic and heterotrophic conditions, the alga can utilize nitrate as well as it does ammonium. The alga metabolizes both glucose and acetate in the dark with a doubling time of 5 to 6 hours. However, its growth on acetate is inhibited by light. Ribulose-1,6-biphosphate carboxylase/oxygenase activity correlates well with photosynthetic capacity, and glucose 6-phosphate dehydrogenase and hexokinase activities are altered in a manner consistent with the availability of glucose in growing cells. The alga appears to assimilate ammonium under photoautotrophic conditions primarily via the glutamine synthetase pathway, and shows an induction of both NADH and NADPH dependent glutamate dehydrogenase pathways under mixotrophic and heterotrophic conditions. Multiple isoforms are present only for hexokinase and glucose 6-phosphate dehydrogenase. Etiolated nitrate-grown cells resume greening and increase their photosynthetic capacity after about 6 hours of incubation in the presence of ammonium under photoautotrophic conditions. Similarly, the loss of photosynthetic capacity in ammonium-grown photoautotrophic cells commence about 9 hours after their transfer to heterotrophic nitrate containing media.     

Changes in the activity of selected enzymes during starvation of Physarum polycephalum

The levels of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, lactate dehydrogenase, and cyclic phosphodiesterase activities were examined in growing and starving plasmodia of Physarum polycephalum. The activities of lactate dehydrogenase, 6-phosphogluconate dehydrogenase, and glucose-6-phosphate dehydrogenase decreased whereas that of cyclic phosphodiesterase increased. The change in activity of lactate dehydrogenase was the result of the variation of the activity of a single enzyme quite similar to the lactate dehydrogenases of higher animals.     

Levels of enzymes of the pentose phosphate pathway in Pachysolen tannophilus Y-2460 and selected mutants

The compositions of intracellular pentose phosphate pathway enzymes have been examined in mutants of Pachysolen tannophilus NRRL Y-2460 which possessed enhanced D-xylose fermentation rates. The levels of oxidoreductive enzymes involved in converting D-xylose to D-xylulose via xylitol were 1.5–14.7-fold higher in mutants than in the parent. These enzymes were still under inductive control by D-xylose in the mutants. The D-xylose reductase activity (EC 1.1.1.21) which catalyses the conversion of D-xylose to xylitol was supported with either NADPH or NADH as coenzyme in all the mutant strains. Other enzyme specific activities that generally increased were: xylitol dehydrogenase (EC 1.1.1.9), 1.2–1.6-fold; glucose-6-phosphate dehydrogenase (EC 1.1.1.49), 1.9–2.6-fold; D-xylulose-5-phosphate phosphoketolase (EC 4.1.2.9), 1.2–2.6-fold; and alcohol dehydrogenase (EC 1.1.1.1), 1.5–2.7-fold. The increase of enzymatic activities, 5.3–10.3-fold, occurring in D-xylulokinase (EC 2.7.1.17), suggested a pivotal role for this enzyme in utilization of D-xylose by these mutants. The best ethanol-producing mutant showed the highest ratio of NADH- to NADPH-linked D-xylose reductase activity and high levels of all other pentose phosphate pathway enzymes assayed.     

Factors involved in changes in hepatic lipogenesis during development of the rat

1. Changes in the activities of acetyl-CoA carboxylase (EC 6.4.1.2), phosphofructokinase (EC 2.7.1.11), aldolase (EC 4.1.2.13), extramitochondrial aconitate hydratase (EC 4.2.1.3) and NADP-dependent isocitrate dehydrogenase (EC 1.1.1.42) have been measured in the livers of developing rats from late foetal life to maturity. 2. The effect of altering the weaning time on some enzymes associated with lipogenesis has been studied. Weaning rats at 15 days of age instead of 21 days results in an immediate increase in the activity of ;malic' enzyme (EC 1.1.1.40) whereas the activities of glucose 6-phosphate dehydrogenase (EC 1.1.1.49) and ATP citrate lyase (EC 4.1.3.8) did not increase until 4-5 days and acetyl-CoA carboxylase 2-3 days after early weaning. Weaning rats on to an artificial-milk diet led to complete repression of the rise in activity of hepatic enzymes associated with lipogenesis normally found on weaning, except for ;malic' enzyme, which increased in activity after 20 days of age. 3. The effect of intraperitoneal injections of glucagon, cortisol, growth hormone and thyroxine on the same hepatic enzymes has been investigated. Only thyroxine had any effect on enzyme activities and caused a 20-fold increase in ;malic' enzyme activity and a twofold increase in ATP citrate lyase activity. 4. The activities of hepatic glucose 6-phosphate dehydrogenase and ;malic' enzyme are higher in adult female than in adult male rats and it has been shown that this sex difference in enzyme activities is due to both male and female sex hormones. 5. Hepatic malate, citrate, pyruvate, glucose 6-phosphate and phosphoenolpyruvate concentrations have been measured throughout development. 6. The results are discussed in relation to the dietary and hormonal control of hepatic enzyme activities during development.     

The preparation of nylon-tube-supported hexokinase and glucose 6-phosphate dehydrogenase and the use of the co-immobilized enzymes in the automated determination of glucose.

Triethyloxonium tetrafluoroborate was used to O-alkylate nylon-tube thus producing the imidate salt of the nylon which was further made to react with 1,6-diaminohexane. 2. Hexokinase (EC 2.7.1.1) and glucose 6-phosphate dehydrogenase (EC 1.1.1.49) were immobilized on the amino-substituted nylon tube through glutaraldeyde and bisimidates. 3. The effect of varying the conditions of O-alkylation and the amount of enzyme immobilized on the activity of nylon tube-hexokinase derivatives was determined. 4. The effect of varying the amount of enzyme immobilized on the activity of nylon-tube-glucose 6-phosphate dehydrogenase derivatives was determined. 5. The thermal stability of nylon-tube-hexokinase and nylon-tube-glucose 6-phosphate dehydrogenase derivatives was studied. 6. Different ratios of hexokinase and glucose 6-phosphate dehydrogenase were co-immobilized on nylon tube, and the rate of conversion of glucose into 6-phosphogluconolactone was compared with the individual activities of the immobilized enzymes. 7. Hexokinase and glucose 6-phosphate dehydrogenase co-immobilized on nylon tube were used in the automated analysis of glucose.     

The effect of streptozotocin-induced diabetes on glycogen metabolism in rat kidney and its relationship to the liver system.

The effects in kidney of streptozotocin-induced diabetes and of insulin supplementation to diabetic animals on glycogen-metabolizing enzymes were determined. Kidney glycogen levels were approximately 30-fold higher in diabetic animals than in control or insulintreated diabetic animals. The activities of glycogenolytic enzymes i.e., phosphorylase (both a and b), phosphorylase kinase, and protein kinase were not significantly altered in the diabetic animals. Glycogen synthase (I form) activity decreased in the diabetic animals whereas total glycogen synthase (I + D) activity significantly increased in these animals. The activities were restored to control values after insulin therapy. Diabetic animals also showed a 3-fold increase in glucose 6-phosphate levels. These data suggest that higher accumulation of glycogen in kidneys of diabetic animals is due to increased amounts of total glycogen synthase and its activator glucose 6-phosphate.     

The pentose phosphate pathway of glucose metabolism. Hormonal and dietary control of the oxidative and non-oxidative reactions and related enzymes of the cycle in adipose tissue

1. Measurements were made of the activities of the enzymes of the pentose phosphate pathway concerned in both the oxidative (glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase) and the non-oxidative (ribose 5-phosphate isomerase, ribulose 5-phosphate epimerase, transketolase and transaldolase) reactions of this pathway, together with hexokinase and phosphoglucose isomerase, in adipose tissue in a variety of nutritional and hormonal conditions. 2. Starvation for 2 days caused a significant decrease in the activities of all the enzymes of the pentose phosphate pathway, with the exception of glucose 6-phosphate dehydrogenase, when expressed as activity/2 fat-pads; only the activities of ribose 5-phosphate isomerase and ribulose 5-phosphate epimerase were significantly decreased on the basis of activity/mg. of protein. Re-feeding with a high-carbohydrate or high-fat diet for 3 days restored the activity of all the enzymes of the pentose phosphate pathway to the range of the control values, with the exception of transketolase, which showed a marked ;overshoot' in rats re-fed with carbohydrate. Starvation for 3 days caused a marked decrease in the activities of glucose 6-phosphate dehydrogenase and transketolase. 3. On the basis of activity/two fat-pads, alloxan-diabetes caused a marked decrease, to about half the control value, in the activities of all the enzymes concerned in the pentose phosphate pathway, transketolase showing the smallest decrease; hexokinase and phosphoglucose isomerase activities were also decreased. Treatment with insulin for 3 and 7 days raised the activities to normal or supranormal values, transketolase showing the most marked ;overshoot' effect. On the basis of activity/mg. of protein the activity of none of the enzymes was significantly decreased in alloxan-diabetes; transketolase and transaldolase activities were raised above the control values. With insulin treatment for 3 or 7 days the activities of all the enzymes were significantly increased, except that of ribulose 5-phosphate epimerase at the shorter time-interval. Glucagon treatment did not alter any of the enzyme activities expressed on either basis. 4. Thyroidectomy caused a decrease of 30-40% in the activities of enzymes of the pentose phosphate pathway, except for transketolase activity, which fell to 50% of the control value. Little change occurred in adipose-tissue weight or protein content. 5. Adrenalectomy caused a decrease of 40% in the activity of glucose 6-phosphate dehydrogenase and of 20-30% in the activities of the remaining enzymes of the pentose phosphate pathway; hexokinase activity was also decreased. Treatment with cortisone for 3 days did not significantly raise the activity from that found in adrenalectomized rats. Treatment of normal rats with high doses of cortisone had no significant effect on the activities of the enzymes of the pentose phosphate pathway in adipose tissue. 6. The changes in enzyme activities are discussed in relation to: (a) the concept of constant-proportion groups of enzymes; (b) the known changes in the flux of glucose through alternative metabolic pathways; (c) the pattern of change found in liver with similar hormonal and dietary conditions.     

Cellobiose catabolism in the haloalkaliphilic hydrolytic bacterium <Emphasis Type="Italic">Alkaliflexus imshenetskii</Emphasis>

Cellobiose metabolism was studied in Alkaliflexus imshenetskii, a haloalkaliphilic hydrolytic bacterium capable of utilizing certain polymers of plant origin, as well as mono- and disaccharides. The major products of cellobiose fermentation by the bacterium were succinate and acetate, and formate was a minor product. Cellobiose could be split into glucose molecules by both β-glucosidase (hydrolytic pathway) and phosphorylase (phosphorolytic pathway); the activity of the former enzyme was two orders of magnitude higher (3600 nmol/(min mg) versus 36 nmol/(min mg)). In cell extracts of the bacterium, high activities of the Embden-Meyerhof-Parnas pathway enzymes—hexokinase, glucose-phosphate isomerase, and phosphofructokinase—were revealed, as well as the activities of glucose-6-phosphate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, and key enzymes of the Entner-Doudoroff pathway—6-phospho-gluconate dehydratase and 2-keto-3-deoxy-6-phospho-gluconate aldolase. Neither the activity of the key enzyme of the hexose-mono-phosphate pathway, 6-phospho-gluconate dehydrogenase, nor the activities of the key enzymes of the modified Entner-Doudoroff pathway, glucose dehydrogenase and 2-keto-3-deoxy-gluconate kinase, were revealed.     

Enzymes of the Glycolytic and Pentose Phosphate Pathways in Proplastids from the Developing Endosperm of Ricinus communis L

The metabolism of sucrose to long chain fatty acids in the endosperm of developing castor bean (Ricinus communis L.) seeds requires a combination of cytosolic and proplastid enzymes. The total activity and the subcellular distribution of the intermediate enzymic steps responsible for the conversion of sucrose to pyruvate have been determined. Hexose phosphate synthesis from sucrose occurs in the cytosol along with the first oxidative step in the pentose phosphate pathway, glucose-6-phosphate dehydrogenase. The proplastids contain the necessary complement of glycolytic enzymes to account for the in vivo rates of acetate synthesis from glucose 6-phosphate. These organelles also contain the majority of the cellular 6-phosphogluconate dehydrogenase, transketolase, and transaldolase activities.     

Modification of NO−3 metabolism in heterocysts of the N2-fixing cyanobacterium Anabaena 7120 (ATCC27893)

Abstract The utilization of NO⁻₃, NO⁻₂ and NH⁺₄ was studied in whole filaments and isolated heterocysts of Anabaena 7120 (ATCC27893). NO⁻₃- and NO⁻₂-uptake were detectable in whole filaments but not in heterocysts, whereas NH⁺₄-uptake was detectable in both. Activity of NO⁻₃-reductase was present in cell-free extracts of whole filaments but not of heterocysts, whereas activities of NO⁻₂-reductase and glutamine synthetase were present in both. NO⁻₃-uptake and reductase activities could not be induced in heterocysts even after prolonged incubation in NO⁻₃ medium. It is suggested that NO⁻₃-metabolism in heterocysts is impaired due to a selective and irreversible loss of NO⁻₃-uptake and reductase systems resulting in the abolition of competition for molybdenum cofactor (Mo-Co) and reductant between nitrogenase and NO⁻₃-reductase, and an increase in glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase levels.     

Automated fluorometric analysis of DNA, protein, and enzyme activities: application to methods in cell culture

Automated fluorometric methods for the analysis of DNA, protein, and selected enzyme activities for N-acetyl-β-d-glucosaminidase, glucose 6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase are described. Instrumentation for these assays includes a Gilford 3500 computer-directed analyzer in conjunction with a Farrand Ratio Fluorometer-2 modified for flowthrough sampling. Comparisons were made between the automated fluorometric methods described and manual spectrophotometric or fluorometric methods for reproducibility, speed of analysis, and quantitative correlation. Typical values of N-acetyl-β-d-glucosaminidase, glucose 6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase activities obtained by these methods in isolated rat hepatocytes and Reuber H-35 hepatoma cells are reported.