Glucose-6-phosphate dehydrogenase-dependent hydrogen peroxide production is involved in the regulation of plasma membrane H+-ATPase and Na+/H+ antiporter protein in salt-stressed callus from Carex moorcroftii

Glucose‐6‐phosphate dehydrogenase (G6PDH) is important for the activation of plant resistance to environmental stresses, and ion homeostasis is the physiological foundation for living cells. In this study, we investigated G6PDH roles in modulating ion homeostasis under salt stress in Carex moorcroftii callus. G6PDH activity increased to its maximum in 100 mM NaCl treatment and decreased with further increased NaCl concentrations. K⁺/Na⁺ ratio in 100 mM NaCl treatment did not exhibit significant difference compared with the control; however, in 300 mM NaCl treatment, it decreased. Low‐concentration NaCl (100 mM) stimulated plasma membrane (PM) H⁺‐ATPase and NADPH oxidase activities as well as Na⁺/H⁺ antiporter protein expression, whereas high‐concentration NaCl (300 mM) decreased their activity and expression. When G6PDH activity and expression were reduced by glycerol treatments, PM H⁺‐ATPase and NADPH oxidase activities, Na⁺/H⁺ antiporter protein level and K⁺/Na⁺ ratio dramatically decreased. Simultaneously, NaCl‐induced hydrogen peroxide (H₂O₂) accumulation was abolished. Exogenous application of H₂O₂ increased G6PDH, PM H⁺‐ATPase and NADPH oxidase activities, Na⁺/H⁺ antiporter protein expression and K⁺/Na⁺ ratio in the control and glycerol treatments. Diphenylene iodonium (DPI), the NADPH oxidase inhibitor, which counteracted NaCl‐induced H₂O₂ accumulation, decreased G6PDH, PM H⁺‐ATPase and NADPH oxidase activities, Na⁺/H⁺ antiporter protein level and K⁺/Na⁺ ratio. Western blot result showed that G6PDH expression was stimulated by NaCl and H₂O₂, and blocked by DPI. Taken together, G6PDH is involved in H₂O₂ accumulation under salt stress. H₂O₂, as a signal, upregulated PM H⁺‐ATPase activity and Na⁺/H⁺ antiporter protein level, which subsequently resulted in the enhanced K⁺/Na⁺ ratio. G6PDH played a central role in the process.     

OESTROGEN EFFECTS ON BRAIN AND PITUITARY ENZYME ACTIVITIES

Abstract— Ovariectomized female rats were treated daily with oestradiol-17β benzoate for intervals up to one week and enzyme activities were measured in the pituitary and various brain regions. Brain regions were selected for study on the basis of their previously demonstrated content of putative oestradiol receptor sites. (1) Pituitary showed oestrogen-dependent increases in glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH) and lactic dehydrogenase (LDH), and no change in NADP⁺-dependent isocitric dehydrogenase (ICDH), NADP⁺-dependent malic dehydrogenase (MDH) or hexokinase (HK). MDH and ICDH were elevated in whole hypothalamus. Enzyme activities did not change significantly in whole amygdala, cerebral cortex, or hippocampus. (2) Sub-regions of the preoptic area, hypothalamus and amygdala were dissected to obtain more highly concentrated populations of cells containing putative oestrogen receptor sites. In the basomedial sub-region of hypothalamus, activities of MDH, ICDH and G6PDH were elevated by oestrogen treatment. In the corticomedial sub-region of amygdala, MDH and ICDH were elevated by oestrogen treatment. No change was observed in any of the six enzymes in medial preoptic area. (3) Increases in enzyme activities were related to the total in vivo dose of oestradiol benzoate given. (4) Hypophysectomy or adrenalectomy did not prevent the enzymatic responses to oestrogen. (S) Oestrogen added directly to the enzyme incubation medium did not change enzyme activities. (6) Weight loss in ovariectomized rats due to reduced food intake did not increase enzyme activities. (7) In the pituitary, good correlation was obtained between the known receptor binding properties of various oestrogenic and non-oestrogenic steroids and the elevation in G6PDH activity. The results indicate that oestradiol acts directly to cause changes in activities of some brain and pituitary enzymes. The possibility is discussed that these changes may result from oestrogen interaction with putative receptor sites found in pituitary and certain brain regions.     

Malate dehydrogenase and glucose-6-phosphate dehydrogenase, key markers for studying the genetic diversity of Actinobacillus actinomycetemcomitans

Abstract Cell-free extracts of strains belonging to the 5 serotypes of A. actinomycetemcomitans were screened for several enzymes. Enzymes representative of the pentose phosphate pathway/hexose monophosphate shunt and the TCA cycle were present. Of these glucose-6-phosphate dehydrogenase (G6PDH) and malate dehydrogenase (MDH) were the most readily detected and stable. MDH and G6PDH retained more than 50% of their activities at alkaline pHs (10–11) for up to 6 h and 3 h at 25°C, respectively, while at pH 6.5, 50% of their activities were lost within 2–3 h. The K _m for malate oxidation catalysed by MDH was 5.8×10⁻⁴ M while that for glucose-6-phosphate oxidation was 2.0×10⁻⁴ M. The pH optima for MDH and G6PDH oxidation activities were 10 and 9.5, respectively. Among the 5 designated serotypes of A. actinomycetemcomitans three groups were delineated by multilocus enzyme electrophoresis using MDH and G6PDH.     

Glucose-6-phosphate dehydrogenase plays a central role in modulating reduced glutathione levels in reed callus under salt stress

In the present study, we investigated the role of glucose-6-phosphate dehydrogenase (G6PDH) in regulating the levels of reduced form of glutathione (GSH) to the tolerance of calli from two reed ecotypes, Phragmites communis Trin. dune reed (DR) and swamp reed (SR), in a long-term salt stress. G6PDH activity was higher in SR callus than that of DR callus under 50–150 mM NaCl treatments. In contrast, at higher NaCl concentrations (300–600 mM), G6PDH activity was lower in SR callus. A similar profile was observed in GSH contents, glutathione reductase (GR) and glutathione peroxidase (GPX) activities in both salt-stressed calli. After G6PDH activity and expression were reduced in glycerol treatments, GSH contents and GR and GPX activity decreased strongly in both calli. Simultaneously, NaCl-induced hydrogen peroxide (H₂O₂) accumulation was also abolished. Exogenous application of H₂O₂ increased G6PDH, GR, and GPX activities and GSH contents in the control conditions and glycerol treatment. Diphenylene iodonium (DPI), a plasma membrane (PM) NADPH oxidase inhibitor, which counteracted NaCl-induced H₂O₂ accumulation, decreased these enzymes activities and GSH contents. Furthermore, exogenous application of H₂O₂ abolished the N-acetyl-l-cysteine (NAC)-induced decrease in G6PDH activity, and DPI suppressed the effect of buthionine sulfoximine (BSO) on induction of G6PDH activity. Western-blot analyses showed that G6PDH expression was stimulated by NaCl and H₂O₂, and blocked by DPI in DR callus. Taken together, G6PDH activity involved in GSH maintenance and H₂O₂ accumulation under salt stress. And H₂O₂ regulated G6PDH, GR, and GPX activities to maintain GSH levels. In the process, G6PDH plays a central role.     

Microfluorometric study of glucose-6-phosphate and malate dehydrogenases in histologically defined areas of the uterus in cyclic and pregnant ewes

Activities of glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49; G6PDH) and malate dehydrogenase (E.C. 1.1.1.37; MDH) were determined fluorometrically in freeze-dried sections of the sheep uterus during the estrous cycle and pregnancy. Samples (0.2–0.3 μg) from the luminal epithelium, uterine glands, maternal caruncles, fetal cotyledons and intercotyledonary trophoblast were assayed in a small aliquot (5 μl) of the reaction medium under oil.Activity of G6PDH in the luminal epithelium, uterine glands and maternal caruncles did not change during the estrous cycle. Activity of MDH in the uterine glands did not change during the cycle, but in the luminal epithelium and maternal caruncles highest activities were found on day 9 and day 2 post-estrus, respectively.The enzyme activities in the fetal tissues were lower than in the maternal tissues. In all maternal tissues, MDH and G6PDH activities decreased during early pregnancy, but after implantation, the activities increased significantly. In fetal tissues G6PDH activity increased, whereas MDH activity decreased during the second half of gestation. These results suggest an increased rate of pentose shunt activity in both maternal and fetal tissues, and an increased rate of Krebs' cycle activity in the maternal but not in the fetal tissues.     

Overexpression of cytosolic malate dehydrogenase (MDH2) causes overproduction of specific organic acids in Saccharomyces cerevisiae

Saccharomyces cerevisiae accumulates l-malic acid through a cytosolic pathway starting from pyruvic acid and involving the enzymes pyruvate carboxylase and malate dehydrogenase. In the present study, the role of malate dehydrogenase in the cytosolic pathway was studied. Overexpression of cytosolic malate dehydrogenase (MDH2) under either the strong inducible GAL10 or the constitutive PGK promoter causes a 6- to 16-fold increase in cytosolic MDH activity in growth and production media and up to 3.7-fold increase in l-malic acid accumulation in the production medium. The high apparent K _m of MDH2 for l-malic acid (11.8 mM) indicates a low affinity of the enzyme for this acid, which is consistent with the cytosolic function of the enzyme and differs from the previously published K _m of the mitochondrial enzyme (MDH1, 0.28 mM). Under conditions of MDH2 overexpression, pyruvate carboxylase appears to be a limiting factor, thus providing a system for further metabolic engineering of l-malic acid production. The overexpression of MDH2 activity also causes an elevation in the accumulation of fumaric acid and citric acid. Accumulation of fumaric acid is presumably caused by high intracellular l-malic acid concentrations and the activity of the cytosolic fumarase. The accumulation of citric acid may suggest the intriguing possibility that cytosolic l-malic acid is a direct precursor of citric acid in yeast. Received: 22 January 1997 / Received revision: 14 April 1997 / Accepted: 19 April 1997     

Isoenzymes of glucose-6-phosphate dehydrogenase from tobacco cells

Two anodic isoenzymes of glucose-6-phosphate dehydrogenase (G6PDH) were isolated from tobacco suspension culture WR-132, utilizing fractional ammonium sulfate precipitation and DEAE-cellulose chromatography. The pH optimum was 9.0 for isoenzyme G6PDH I and 8.0–8.3 for G6PDH IV. Isoenzyme G6PDH I exhibited Michaelis-Menten kinetics for both substrates, G6P and NADP⁺, with K_m's of 0.22 mM and 0.06 mM, respectively. G6PDH IV exhibited Michaelis-Menten kinetics for G6P with a K_m of 0.31 mM. The NADP⁺ double reciprocal plot showed an abrupt transition between two linear sections. This transition corresponds to an abrupt increase in the apparent K_m and V_max values with increasing NADP⁺, denoting negative cooperativity. The two K_m's for high and low NADP⁺ concentrations were 0.06 mM and 0.015 mM, respectively. MWs of the isoenzymes as determined by SDS disc gel electrophoresis were 85 000–91 000 for G6PDH I and 54 000–59 000 for G6PDH IV. Gel filtration chromatography on Sephadex G-150 showed MW's of 91 000 for G6PDH I and 115 000 for G6PDH IV. A probable dimeric structure for IV is suggested, with two NADP⁺ binding sites.     

Enhanced production of GDP-<Emphasis Type="SmallCaps">l</Emphasis>-fucose by overexpression of NADPH regenerator in recombinant <Emphasis Type="Italic">Escherichia coli</Emphasis>

Biosynthesis of guanosine 5′-diphosphate-l-fucose (GDP-l-fucose) requires NADPH as a reducing cofactor. In this study, endogenous NADPH regenerating enzymes such as glucose-6-phosphate dehydrogenase (G6PDH), isocitrate dehydrogenase (Icd), and NADP⁺-dependent malate dehydrogenase (MaeB) were overexpressed to increase GDP-l-fucose production in recombinant Escherichia coli. The effects of overexpression of each NADPH regenerating enzyme on GDP-l-fucose production were investigated in a series of batch and fed-batch fermentations. Batch fermentations showed that overexpression of G6PDH was the most effective for GDP-l-fucose production. However, GDP-l-fucose production was not enhanced by overexpression of G6PDH in the glucose-limited fed-batch fermentation. Hence, a glucose feeding strategy was optimized to enhance GDP-l-fucose production. Fed-batch fermentation with a pH-stat feeding mode for sufficient supply of glucose significantly enhanced GDP-l-fucose production compared with glucose-limited fed-batch fermentation. A maximum GDP-l-fucose concentration of 235.2 ± 3.3 mg l⁻¹, corresponding to a 21% enhancement in the GDP-l-fucose production compared with the control strain overexpressing GDP-l-fucose biosynthetic enzymes only, was achieved in the pH-stat fed-batch fermentation of the recombinant E. coli overexpressing G6PDH. It was concluded that sufficient glucose supply and efficient NADPH regeneration are crucial for NADPH-dependent GDP-l-fucose production in recombinant E. coli.     

Heterotrophy and nitrate metabolism in a cyanobacteriumPhormidium uncinatum

Nitrate-supported heterotrophic growth ofPhormidium uncinatum was achieved after repeated exposure to glucose in the presence of a photosystem (PS) II inhibitor. Nitrate and glucose utilization as well as activities of their metabolizing enzymes were measured comparatively in photoautotrophic and heterotrophic cells. Nitrate and glucose were taken up together at the ratio of 1:8 (molar basis) and glucose catabolism via glucose-6-phosphate dehydrogenase (G6PDH), and 6-phosphogluconate dehydrogenase (6PGDH) activities transferred desired electrons for nitrate reduction to ammonia through coupled ferredoxin-NADP⁺ reductase (FNR) activity. Ammonia thus generated was assimilated mainly by NADPH-glutamate dehydrogenase (GDH) activity. These data demonstrate an operation of nitrate assimilation in this cyanobacterium under heterotrophic conditions.     

Malic dehydrogenase from tamarix roots: effects of sodium chloride in vivo and in vitro

Soluble and mitochondrial malic dehydrogenases (MDH) were isolated from root tips of the halophyte Tamarix tetragyna L. grown in the presence and absence of NaCl. The activity of the enzymes isolated from root tips grown in the presence of NaCl was lower than that of the enzymes isolated from roots grown in absence of NaCl. The mitochondrial MDH was much more sensitive to salinity than the soluble MDH. The soluble enzyme from roots grown in NaCl had a higher Km for malate and lower Km for NAD than enzyme from the control roots. Addition of NaCl in vitro at 72 mM significantly stimulated the reductive activity of soluble MDH, while higher NaCl concentrations (240 mM and above) depressed enzyme activity. The inhibition of enzyme activity by various salts was found to be in the order MgCl₂ > NaCl = KCl > Na₂SO₄. Mannitol at equiosmotic concentrations had no effect. Substrate inhibition, typical for oxaloacetate oxidation, was not observed at high NaCl concentrations in vitro and high substrate concentrations neutralized the inhibitory effect of NaCl. Increased coenzyme concentrations had no effect. In vitro NaCl increased the Km for malate and oxaloacetate already at relatively low concentrations. At the same time NaCl decreased the Km for NAD and NADH. The inhibitory effect of NaCl on enzyme activity seems not to be due to the effect on the Km alone. Soluble and mitochondrial MDH had different responses to pH changes, mitochondrial MDH being more sensitive. Mitochondrial MDH released from the particles had a similar response to that of the entire particles. Changes of pH modified the effect of NaCl on enzyme activity. It was postulated that NaCl apparently induces conformational changes in the enzyme.     

Expanded bed affinity chromatography of dehydrogenases from bakers' yeast using dye-ligand perfluoropolymer supports

Malate dehydrogenase (MDH) and glucose 6-phosphate dehydrogenase (G6PDH) have been partially purified from preparations of homogenized yeast cells using Procion Yellow H-E3G and Procion Red H-E7B, respectively, immobilized on solid perfluoropolymer supports in an expanded bed. A series of pilot experiments were carried out in small packed beds using clarified homogenate to determine the optimal elution conditions for both MDH and G6PDH. Selective elution of MDH using NADH was effective but the yields obtained were dependent on the concentration of NADH used. Selective elution was found to be most effective when a low concentration of NaCl (0.1 M) was present. MDH could be recovered in 84% yield with a purification factor of 94 when this strategy was adopted. In the case of G6PDH, specific elution using NADP(+) was successful in purifying G6PDH 178-fold in 96% yield. The dynamic capacity of both affinity supports was estimated by frontal analysis, in an expanded bed with unclarified homogenate, and corresponded to 17 U MDH/mL of settled Procion Yellow H-E3G perfluoropolymer support and 7.7 U H6PDH/mL of settled Procion Red H-E7B perfluoropolymer support. Expanded bed affinity chromatography of MDH resulted in an eluted fraction containing 89% of the applied activity with a purification factor of 113. Expanded bed affinity chromatography of G6PDH resulted in an eluted fraction containing 84% of the applied activity with a purification factor of 172. With both enzymes, the overall recovery of enzyme activity was greater than 94%, showing that the expanded bed approach to purification was nondenaturing. (c) 1995 John Wiley & Sons, Inc.     

Responses of amino acid metabolizing enzymes from plants differing in salt tolerance to NaCl

Summary This paper reports the effects of NaCl on the in vivo activity of glutamate dehydrogenase (GDH) and glutamic-oxaloacetic transaminase (GOT) and on the in vitro activity of GDH, both enzymes having been isolated from plants differing in salt tolerance. The plants investigated were Vicia faba (salt-sensitive), Atriplex nitens and Atriplex calotheca (more or less salt-tolerant), and Atriplex halimus (halophyte) grown at various NaCl concentrations. GDH and GOT isolated from various salt-tolerant plants grown at low NaCl concentrations were inhibited in a similar way. At high NaCl concentrations, the enzyme activities remain at constant values only in the Atriplex species. GOT was more impaired by NaCl than GDH. In the case of GOT, the double reciprocal plot indicated the type of a noncompetitive inhibition. The in vitro effect of NaCl on the activity of GDH from the differentially salt-tolerant plants was of a different kind, i.e. GDH isolated from V. faba was clearly inhibited by NaCl, whereas NaCl stimulated the activity of GDH from all Atriplex species investigated. Kinetic analysis showed that substrate inhibition of GDH from A. nitens and A. calotheca grown at non-saline conditions could be removed by NaCl. Inhibition by high NaCl concentrations at low substrate concentrations was removable by increasing substrate concentrations. Moreover, the inhibition at low substrate concentrations was shown to be competitive. GDH lost this regulatory property when the plants were pretreated with 500 mM NaCl. GDH from A. halimus also possessed this control, but in contrast to A. nitens and A. calotheca, activity and control of GDH isolated from A. halimus were stimulated by pretreating the plants with 500 mM NaCl. The results showed that DDH isolated from the salt-tolerant Atriplex species was adapted to high NaCl concentrations of the tissue. Possible mechanisms of the interactions between GDH from salt-tolerant Atriplex species and NaCl are discussed.     

The influence of temperature on glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and the regulation of these enzymes in a mesophilic and a thermophilic cyanobacterium

The activities and kinetics of the enzymes G6PDH (glucose-6-phosphate dehydrogenase) and 6PGDH (6-phosphogluconate dehydrogenase) from the mesophilic cyanobacterium Synechococcus 6307 and the thermophilic cyanobacterium Synechococcus 6716 are studied in relation to temperature. In Synechococcus 6307 the apparent K _m's are for G6PDH: 80M (substrate) and 20M (NADP⁺); for 6PGDH: 90M (substrate) and 25M (NADP⁺). In Synechococcus 6716 the apparent K _m's are for G6PDH: 550M (substrate) and 30M (NADP⁺); for 6PGDH: 40M (substrate) and 10M (NADP⁺). None of the K _m's is influenced by the growth temperature and only the K _m's of G6PDH for G6P are influenced by the assay temperature in both organisms. The idea that, in general, thermophilic enzymes possess a lower affinity for their substrates and co-enzymes than mesophilic enzymes is challenged.Although ATP, ribulose-1,5-bisphosphate, NADPH and pH can all influence the activities of G6PDH and 6PGDH to a certain extent (without any difference between the mesophilic and the thermophilic strain), they cannot be responsible for the total deactivation of the enzyme activities observed in the light, thus blocking the pentose phosphate pathway.Abbreviations G6PDH glucose-6-phosphate, dehydrogenase - 6PGDH 6-phosphogluconate dehydrogenase - G6P glucose-6-phosphate - 6PG 6-phosphogluconate - RUDP ribulose-1,5-bisphosphate - Tricine N-Tris (hydroxymethyl)-methylglycine     

Role of hydrogen peroxide in regulating glucose-6-phosphate dehydrogenase activity under salt stress

The role of hydrogen peroxide in the regulation of glucose-6-phosphate dehydrogenase (G6PDH) activity in the red kidney bean (Phaseolus vulgaris L.) roots under salt stress (100 mM NaCl) was investigated. Salt stress caused the increase of the activities of G6PDH and antioxidative enzymes including ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), as well as H₂O₂ production. The application of H₂O₂ (1 mM) also enhanced the activities of G6PDH as well as antioxidative enzymes. In the presence of exogenous CAT, H₂O₂ content was decreased, and the enhanced activities of G6PDH and antioxidative enzymes induced by NaCl or by exogenous H₂O₂ were also abolished, suggesting that the enhancement of the above enzyme activities under salt stress was a result of the increased endogenous H₂O₂ levels. Further results showed that the effects of NaCl and H₂O₂ on the activities of antioxidative enzymes were diminished by Na₃PO₄ (a G6PDH inhibitor), suggesting G6PDH activity is required in enhancing the activities of antioxidative enzymes. The enhanced membrane leakage, lipid peroxidation, H₂O₂ and O₂ — contents, G6PDH and antioxidative enzyme activities under salt stress were all recovered to control level when the red kidney bean seedlings treated with 100 mM NaCl for 6 d were transferred to the control conditions for 8 d.     

Caractérisation de la glutamate déshydrogénase chez un halophyte obligatoire: le Suaeda maritima var. macrocarpa

Characterization of the glutamate dehydrogenase from an obligate halophyte: Suaeda maritima var. macrocarpa The glutamate dehydrogenase (GDH), E.C. 1.4.1.3, of the obligate halophyte Suaeda maritima (L.) Dum. var. macrocarpa Moq. has been studied. NaCl increase in the culturing solution (0 to 23 g NaCl/litre) lowers the specific activity but does not affect the kinetic characteristics of the enzyme collected after purification on G-25 Sephadex gel. In optimal conditions, GDH is activated by the addition of 25 mM NaCl in the incubation medium and inhibited with concentrations over 100 mM. The inhibitory activity of the salt induces both a modification of the affinity of the enzyme for substrate (competitive inhibition for ketoglutarate) and a modification of the catalytic potency (non-competitive inhibition with NADH and ammonium ion). It is suggested that NaCl has a depressing influence on GDH synthesis. There is a fundamental difference between its short time action (in vitro) versus its continuous effect in the culturing solution.     

Chemopreventive effect of piperine on mitochondrial TCA cycle and phase-I and glutathione-metabolizing enzymes in benzo(a)pyrene induced lung carcinogenesis in Swiss albino mice

Piperine is a major component of black (Piper nigrum Linn) and long pepper (Piper longum Linn) used widely in various systems of traditional medicine. We have evaluated the effect of piperine on mitochondrial tricarboxylic acid cycle and phase I and glutathione-metabolizing enzymes in Benzo(a)pyrene induced experimental lung carcinogenesis in swiss albino mice. Lung cancer bearing mice showed a significant decrease in the activities of mitochondrial enzymes-isocitrate dehydrogenase (ICDH), -ketoglutarate dehydrogenase (KDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and significantly increased NADPH-Cytochorome reductase (NADPH-C reductase), cytochrome P450 (cyt-p450) and cytochrome b5(cyt-b5). The activities of glutathione-metabolizing enzymes glutathione peroxidase(GPx), glutathione reductase (GR) and glucose-6-phospho dehydrogenase(G6PDH) were significantly lowered in lung-cancer bearing mice when compared with control mice. Piperine supplementation to tumour-induced animals significantly lowered the phase-I enzymes (NADPH-C reductase, cyt-p450 and cyt-b5)) and there was a rise in glutathione-metabolizing enzymes (GPx, GR and G6PDH), which indicated an antitumour and anti-cancer effect. Comparison of normal control mice and mice administered piperine only as drug control showed no significant variations in enzyme activities. Piprine administration to benzo(a)pyrene induced animals significantly increased the activities of mitochondrial enzymes, thereby suggesting its role in mitochondrial energy production.     

Metabolic background for establishment of the subpopulation structure in early ontogenesis in the Atlantic salmon (the case of energy of carbohydrate metabolism)

The activity of some enzymes involved in energy and carbohydrate metabolism was studied in Atlantic salmon embryos at the eyed egg stage and in salmon fingerlings (0+) from two trophic–ecological groups: the Varzuga River bed and two tributaries, the Pyatka and Sobachii rivers (Kola Peninsula). It has been demonstrated that heterogeneity of embryos was most evident in the case of cytochrome c oxidase (CO), malate dehydrogenase (MDH), glycerol-1-phosphate dehydrogenase (G1PDH), and glucose-6-phosphate dehydrogenase (G6PDH), while the lowest level of heterogeneity was observed for lactate dehydrogenase (LDH) and aldolase. A positive correlation was revealed between the activities of CO, LDH, MDH, and G1PDH. It was noted that G6PDH showed a negative correlation with almost all enzymes under study. It was found that salmon juveniles inhabiting the tributaries were characterized by high LDH, aldolase, and G1PDH activity and lower activity of G6PDH compared to the juveniles inhabiting the main river bed. Notably, the differences in the activity of the enzymes involved in aerobic metabolism between the two groups of fingerlings under analysis were observed only in the autumn.     

Enzymes of ammonium assimilation inStreptomyces avermitilis

Glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), alanine dehydrogenase (ADH) and alanine aminotransferase (GPT) were detected in the cell-free homogenate ofStreptomyces avermitilis grown in a defined medium containing ammonium sulfate as the only nitrogen source. At an initial NH₄ ⁺ concentration of 7.5 mmol/L, high activities of GS, GOGAT and GDH were found while that of ADH was low. The ADH activity was markedly increased at initially millimolar NH₄ ⁺ concentrations. In some characteristics of its NH₄ ⁺-assimilating system (e.g. control of some enzyme activities, the NADPH specificity of GOGAT, the presence of alanine aminotransferase),S. avermitilis differs from other known streptomycetes.     

Glucose-6-phosphate dehydrogenase and malate dehydrogenase enzyme electrophoretic patterns amongst strains of Bacteroides fragilis

Fifty-two strains of Bacteroides fragilis were examined for their enzyme electrophoretic patterns of glucose-6-phosphate dehydrogenase (G6PDH) and malate dehydrogenase (MDH). All strains tested possessed high levels of both enzymes but the G6PDH reduced NADP whereas MDH was NAD-dependent. Twenty-seven strains produced single bands of both G6PDH and MDH. In all cases G6PDH migrated faster than MDH. Strains clustered by a single linkage algorithm were recovered in eight clusters at the 77% similarity level. The remaining 25 strains produced multiple bands of one or both enzymes. These were recovered in six clusters at the 72% similarity level using the same algorithm. The results of this study revealed considerable heterogeneity of enzyme patterns within B. fragilis.     

Effects of temperature on germination and mitochondrial dehydrogenases in two soybean (Glycine max) cultivars

The effects of eight germination temperatures from 10°C to 35°C on germination and dehydrogenase activities of two soybean (Glycine max [L.] Merr.) cultivars were investigated after 48 h of seedling growth. Axis fresh weights of cv. Chippewa increased as germination temperature increased from 10°C to 35°C. In contrast, axis fresh weights for the cv. Wells increased more slowly with increasing temperature and reached a maximum at c. 25°C. In general, in vitro activities of glutamate dehydrogenase (GDH), NADP-isocitrate dehydrogenase (NADP-ICDH), and malate dehydrogenase (MDH) from the axes of cv. Chippewa correlated well with increases in axis fresh weights. GDH and MDH activities from axes of the cv. Wells also reflected increases in axis fresh weights although the correlation was not as evident as for the cv. Chippewa. NADP-ICDH activity from ‘Wells’ axes was highest at 35°C even though germination was poor at this temperature. GDH and MDH activities from cotyledons of both cultivars were not correlated with axis weight increases. No GDH activity was detected in ‘Wells’ cotyledons from seeds germinated at 35°C.