Activities Of 6PGDH Research Articles

The role of respiratory metabolism in chilling injury development of Chinese olive fruit during cold storage

Chilling injury (CI) and browning occurrence are pivotal issues during the cold storage of postharvest Chinese olive fruit. This study evaluates the effects of non-chilling temperature (8 °C) and chilling temperature (2 °C) on CI development, browning occurrence, and respiratory metabolism in postharvest Chinese olives. Compared to storage at 8 °C, storage at 2 °C significantly induced CI, accompanied by higher indices of CI and browning, as well as a higher fruit respiratory rate. Storage at 2 °C increased the activities of phosphohexose isomerase (PGI), succinate dehydrogenase (SDH), ascorbic acid oxidase (AAO), and cytochrome C oxidase (CCO) by 55.1%, 11.1%, 26.4%, and 98.8%, respectively, on day 120. On the other hand, storage at 2 °C reduced the activities of NAD kinase (NADK), 6-phosphogluconate dehydrogenase (6-PGDH) + glucose-6-phosphate dehydrogenase (G-6-PDH) by 95.6% and 6.6%, respectively, on day 120. The contents of nicotinamide adenine dinucleotide (NAD) and its reduced form of NAD (NADH) increased by 10.0% and 22.8%, respectively, in fruit stored at 2 °C on day 120. Conversely, the contents of nicotinamide adenine dinucleotide phosphate (NADP) and its reduced form (NADPH) decreased by 58.3% and 64.4%, respectively, in fruit stored 2 °C on day 120. These findings indicate that CI development and browning occurrence in Chinese olives induced by storage at 2 °C were associated with a higher respiratory rate, increased activities of PGI, SDH, AAO, and CCO, higher contents of NAD(H), reduced activities of 6-PGDH + G-6-PDH, and lower contents of NADP(H).

Effects of Drought Stress on Key Enzymes of Carbon Metabolism, Photosynthetic Characteristics and Agronomic Traits of Soybean at the Flowering Stage under Different Soil Substrates

Soybean is an important legume food crop, and its seeds are rich in nutrients, providing humans and animals with edible oil and protein feed. However, soybean is sensitive to water requirements, and drought is an important factor limiting soybean yield and quality. This study used Heinong 84 (drought resistant variety) and Hefeng 46 (intermediate variety) as tested varieties planted in chernozem, albic, and black soils. The effects of drought stress on the activities of key enzymes in carbon metabolism and photosynthetic characteristics of soybean were studied during the flowering stage, most sensitive to water. (1) The activities of SS-1, 6PGDH, and G6PDH enzymes in soybean leaves first increased and then decreased under drought stress. The enzyme activity was the highest under moderate drought stress and weakest in the blank group. (2) Drought stress increased Phi2, PhiNO, and Fm in soybean leaves and reached the highest value under severe drought; with the increase in drought stress, PhiNPQ and Fv/Fm of soybean leaves gradually decreased, reaching the lowest under severe drought. (3) With the increase in drought stress, F0 and Fs of soybean leaves showed a single peak curve, and the maximum was at moderate drought. (4) Correlation analysis showed that F0 was greatly affected by varieties and soil types; Fs, F0, and Fm soil varieties had a great influence, and chlorophyll fluorescence parameters were affected differently under drought stress with different drought degrees. (5) Drought stress changed the agronomic traits and yield of soybean. With the increase of drought degree, plant height, node number of main stem, effective pod number, 100-seed weight and total yield decreased continuously. (6) Drought stress affected the dry matter accumulation of soybean. With the increase of drought degree, the dry matter accumulation gradually decreased. Among them, the leaf was most seriously affected by drought, and SD decreased by about 55% compared with CK. Under the condition of black soil, the dry matter accumulation of soybean was least affected by drought.

Molecular mechanisms of furanone production through the EMP and PP pathways in Zygosaccharomyces rouxii with D-fructose addition

4-Hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) and 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF) are important aroma chemicals in fermented foods. In this study, transcriptomics, qRT-PCR and enzymology methods were used to study the molecular mechanisms of furanone production through the Embden-Meyerhof-Parnas (EMP) and Pentose Phosphate (PP) pathways in Zygosaccharomyces rouxii based on the results of our previous study. The results indicated that D-fructose addition could significantly enhance Z. rouxii biomass production. In addition, HDMF and HEMF production was increased as a result of D-fructose addition based on HPLC analysis. The significant pathways for furanone synthesis were EMP (zro00010) and PP (zro00030) based on KEGG analysis. At the mRNA level, the differentially expressed genes involved in HDMF and HEMF biosynthesis were HK, PFK1, G6PI, FBA, TPI, 6GPL, TKT, and 6PGDH. Transient overexpression of FBA and 6PGDH in Z. rouxii was significantly increased during furanone production. FBA can regulate the accumulation of dihydroxyacetone phosphate (DHAP), which is one of the precursors of HDMF, while 6PGDH can regulate the accumulation of ribulose-5-phosphate, a precursor of HEMF. In addition, the activities of PFK1, FBA, and 6PGDH were significantly correlated with furanone production. LC-MS/MS results indicated that the primary metabolites for furanone synthesis in the EMP and PP pathways gradually increased with the consumption of D-fructose. These data demonstrate that D-fructose addition can be used to generate furanones through the EMP and PP pathways in Z. rouxii.

Effects of Timolol Treatment on Pancreatic Antioxidant Enzymes in Streptozotocin-induced Diabetic Rats: An Experimental and Computational Study.

SummaryBackgroundThe study aimed to investigate whether timolol-treatment has a beneficial effect on pentose phosphate pathway enzyme activities such as glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGDH) enzyme activities and cAMP level in streptozotocin-induced diabetic rats in pancreatic tissuesMethodsDiabetes was induced by streptozotocin (STZ) in 3-month old male Wistar rats. The diabetic rats were treated with timolol (5 mg/kg body weight, for 12 weeks) while the control group received saline. Enzyme activities were determined in pancreas tissue. To support our results, we performed in silico calculations, using Protein Data Bank structures.ResultsTimolol treatment of STZ-induced diabetic rats had no noteworthy effect on high blood-glucose levels. However, this treatment induced activities of G6PD and 6PGDH in diabetic rats. Timolol treatment significantly increased cAMP level in diabetic pancreatic tissue. We found that timolol cannot bind strongly to either G6PD or 6PGD, but there is a relatively higher binding affinity to adenylyl cyclase, responsible for cAMP production, serving as a regulatory signal via specific cAMP-binding proteins.ConclusionsOur data point out that timolol treatment has beneficial effects on the antioxidant defence mechanism enzymes in the pancreas of STZ-induced diabetic rats.

Differential effects of exposure to parasites and bacteria on stress response in turbot Scophthalmus maximus simultaneously stressed by low water depth.

The stress response of turbot Scophthalmus maximus was evaluated in fish maintained 8 days under different water depths, normal (NWD, 30 cm depth, total water volume 40 l) or low (LWD, 5 cm depth, total water volume 10 l), in the additional presence of infection-infestation of two pathogens of this species. This was caused by intraperitoneal injection of sublethal doses of the bacterium Aeromonas salmonicida subsp. salmonicida or the parasite Philasterides dicentrarchi (Ciliophora:Scuticociliatida). The LWD conditions were stressful for fish, causing increased levels of cortisol in plasma, decreased levels of glycogen in liver and nicotinamide adenine dinucleotide phosphate (NADP) and increased activities of G6Pase and GSase. The presence of bacteria or parasites in fish under NWD resulted in increased cortisol levels in plasma whereas in liver, changes were of minor importance including decreased levels of lactate and GSase activity. The simultaneous presence of bacteria and parasites in fish under NWD resulted a sharp increase in the levels of cortisol in plasma and decreased levels of glucose. Decreased levels of glycogen and lactate and activities of GSase and glutathione reductase (GR), as well as increased activities of glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH) and levels of nicotinamide adenine dinucleotide phosphate (NADPH) occurred in the same fish in liver. Finally, the presence of pathogens in S. maximus under stressful conditions elicited by LWD resulted in synergistic actions of both type of stressors in cortisol levels. In liver, the presence of bacteria or parasites induced a synergistic action on several variables such as decreased activities of G6Pase and GSase as well as increased levels of NADP and NADPH and increased activities of GPase, G6PDH and 6PGDH.

Effect of Panax ginseng on some changed biochemical parameters in alloxan-induced diabetic rats

Background: Panax ginseng root contains insulin like substances beside a mixture of saponin compounds responsible for its antioxidant activity. Objectives: The present work was carried out to investigate the effect of ginseng root extract (GRE) on some biochemical parameters in alloxan induced diabetic rats. Methods: Rats were divided into two main groups, the first group (control group) and the second group (diabetic group) in which the healthy rats were rendered diabetic, after 18 hours fasting, by a subcutaneous injection of a single dose of alloxan (120 mg/kg Body Weight “BW”). Three diabetic subgroups were treated orally with a daily dose of GRE (100 mg/kg BW) for 7, 14, and 21days, respectively. However, three subgroups were left diabetic without treatment for 7, 14, and 21 days. Results: Glucose 6- phosphate dehydrogenase (G6PDH) and 6-phospho-gluconate dehydrogenase (6PGDH) activities were significantly (P<0.0001) increased in the kidney extract of the diabetic rats after one week of diabetes induction. However, their activities in the liver extract were significantly decreased. Treatment of diabetic rats with GRE for 3 weeks showed restoration of the activities of G6PDH and 6PGDH in both kidney and liver. The abnormal elevations of kidney weight and the levels of glucose, glucose-6-phosphate, fructose and sorbitol in the kidney were markedly improved after treatment of diabetic rats with GRE. In addition, the level of serum glucose and potassium were significantly (p<0.0001) increased in all diabetic groups compared to control group. Conversaly, serum sodium level was decreased (hyponatreimia) in all diabetic groups. Treatment of diabetic rats with a single daily dose of GRE (100mg/BW) improved the abnormal changes of these parameters over all the periods of treatment especially after the 21 days of treatment.

Potential antitumour and pro-oxidative effects of (E)-methyl 2-(7-chloroquinolin-4-ylthio)-3-(4-hydroxyphenyl) acrylate (QNACR)

Context: Characterization of the pro-oxidant activity of QNACR.Objectives: Reactive oxygen species (ROS) induce cellular damage and represent unique opportunities to kill malignant cells. In this study, we synthesized and evaluated the new compound, (E)-methyl 2-(7-chloroquinolin-4-ylthio)-3-(4-hydroxyphenyl) acrylate (QNACR) as potential pro-oxidative agent against breast cancer.Methods: Oxidative stress biomarkers such as ROS, thiobarbuturic acid reactive species (TBARs) and different antioxidant enzyme activities were determined in cell lysates.Results: QNACR showed cytotoxic and more selective effects to tumour MCF7 cells (IC50 < 25 µM) compared to antitumour controls, inducing ROS and TBARs parallel to inhibitions of catalase (CAT), glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). Longer exposures to QNACR triggered adaptive effects increasing the overall activities of CAT, glutathione reductase, G6PDH and 6PGDH, but eventually the adaptation changes faded and cells died.Conclusion: QNACR led to remarkable modifications in the oxidative status of tumour cells, proposing this compound as potential alternative for antitumour therapy.

Effects of regulators on the respiratory enzyme of pear branches during dormant period

The effects of regulators on the respiratory enzymes of Qiyuesu’s pear branches during dormant period were studied. The results showed that enzyme activities of SDH, G-6-PDH and 6-PGDH were increased by 0.02 mmol/L SA and 120 mg/L GA3. The enzyme activities of phosphohexoisomerase were reduced by 0.02 mmol/L SA and 120 mg/L GA3. Compared with the control, the PGI activity was reduced by 20.5% and 13.6% using 0.02mmol/L SA and 120mg/L GA3. Similarly, the SDH activity was increased by 6.1% and 29.2%, respectively. Likewise, the activity of G-6-PDH and 6-PGDH was increased by 93.9% and 24.8%. Changes of respiratory enzymes were consistent with respiratory pathway of regulators, which indicated that SA and GA3 were helpful to break the dormancy by enhancing activities of SDH, G-6-PDH and 6-PGDH.

The 6‐phosphogluconate Dehydrogenase Genes Are Responsive to Abiotic Stresses in Rice

AbstractGlucose‐6‐phosphate dehydrogenase (G6PDH, E.C. 1.1.1.49) and 6‐phosphogluconate dehydrogenase (6PGDH, EC 1.1.1.44) are both key enzymes of the pentose phosphate pathway (PPP). The OsG6PDH1 and Os6PGDH1 genes encoding cytosolic G6PDH and cytosolic 6PGDH were isolated from rice (Oryza sativa L.). We have shown that Os6PGDH1 gene was up‐regulated by salt stress. Here we reported the isolation and characterization of Os6PGDH2 from rice, which encode the plastidic counterpart of 6PGDH. Genomic organization analysis indicated that OsG6PDH1 and OsG6PDH2 genes contain multiple introns, whereas two Os6PGDH1 and Os6PGDH2 genes have no introns in their translated regions. In a step towards understanding the functions of the pentose phosphate pathway in plants in response to various abiotic stresses, the expressions of four genes in the rice seedlings treated by drought, cold, high salinity and abscisic acid (ABA) were investigated. The results show that OsG6PDH1 and OsG6PDH2 are not markedly regulated by the abiotic stresses detected. However, the transcript levels of both Os6PGDH1 and Os6PGDH2 are up‐regulated in rice seedlings under drought, cold, high salinity and ABA treatments. Meanwhile, the enzyme activities of G6PDH and 6PGDH in the rice seedlings treated by various abiotic stresses were investigated. Like the mRNA expression patterns, G6PDH activity remains constant but the 6PGDH increases steadily during the treatments. Taken together, we suggest that the pentose phosphate pathway may play an important role in rice responses to abiotic stresses and the second key enzyme of PPP, 6PGDH, may function as a regulator controlling the efficiency of the pathway under abiotic stresses.(Handling editor: Kang Chong)

Effect of Various Combinations of Growth Temperature, pH and NaCl on Intracellular Activities of G6PDH and 6PGDH from Four Bacillus strains isolated from Jordanian Hot springs

Effect of Various Combinations of Growth Temperature, pH and NaCl on Intracellular Activities of G6PDH and 6PGDH from Four Bacillus strains isolated from Jordanian Hot springs

Effects of excess corticosterone on NADPH generating enzymes and glucose oxidation in Leydig cells of adult rats

Clinical and experimental studies have shown the adverse effects of excess glucocorticoid on testicular testosterone production. The NADPH co-enzyme has been recognized as an important factor that regulates several steps in steroidogenesis, while glucose oxidation acts as a limiting factor on testicular testosterone production. Nevertheless, the impact of excess corticosterone, the stress hormone on testicular NADPH availability and glucose oxidation is unknown. Therefore, the present study was designed to assess the specific effects of excess corticosterone on Leydig cell NADPH generating enzymes and glucose oxidation. Adult Wistar rats (200-250 g, b.w.) were treated with corticosterone-21-acetate (2 mg/ 100 g, b.w., i.m., twice daily) for 10 days and corticosterone-21-acetate plus luteinizing hormone (LH) (100 microg/kg b.w., i.m., daily) for 10 days. After the treatment period, experimental animals and controls were killed, blood was collected and the sera separated for testosterone assay. Testes were removed and Leydig cells were isolated, purified and used for estimating the specific activity of NADPH generating enzymes and 14C-glucose oxidation. Serum testosterone, Leydig cellular 14C-glucose oxidation and the specific activities of 6-phosphogluconate dehydrogenase (6-PGDH), NADP-isocitrate dehydrogenase (ICDH) and malic enzyme were significantly decreased in corticosterone-treated rats. Co-administration of LH with corticosterone maintained the specific activities of 6-PGDH and ICDH and 14C-glucose oxidation at control level. Nevertheless, serum testosterone and Leydig cellular malic enzyme activity showed a significant decrease in these rats. In conclusion, the inhibitory effects of excess corticosterone on Leydig cell steroidogenesis are mediated through impaired glucose oxidation and defective NADPH generation. Co-administration of LH with corticosterone failed to prevent the decrease in serum testosterone and Leydig cell malic enzyme activity, suggesting the dominant inhibitory effects of excess corticosterone.

Changes in key enzymes of viral-RNA biosynthesis in chloroplasts from PVY and TMV infected tobacco plants

Effects of the infection with tobacco mosaic virus (TMV) and potato virus Y (PVY) on chloroplasts from susceptible tobacco plants were determined. Changes in ribonucleases (RNases), phosphomonoesterase (PME), phosphodiesterase (PDE), glucose-6-phosphate dehydrogenase (G6P DH), 6-phosphogluconate dehydrogenase (6PG DH), glucokinase (GK), and fructokinase (FK) activities in thylakoid/envelope and stroma fractions were studied. Slight increase in the activities of PME, PDE, G6P DH and 6PG DH of thylakoid/envelope fraction as well as of RNases, PME, PDE, G6P DH, 6PG DH, GK and FK of stroma fraction was found in chloroplasts isolated from leaf tissues infected with PVY. Infection with TMV produced higher increase in enzymes activities in chloroplasts; especially, PME, G6P DH and 6PG DH in fraction of thylakoid/envelope, and RNases, PME, PDE, G6P DH, 6PG DH, and GK in stroma fraction.

Effect of dietary lipid level on growth performance, lipid deposition, hepatic lipogenesis in juvenile cobia ( Rachycentron canadum)

A study was undertaken to evaluate the effect of the dietary lipid level on growth, feed utilization, lipid deposition and lipid metabolism by cobia juveniles. Three isonitrogenous diets containing 47% crude protein with increasing dietary lipid levels 5%, 15% and 25% (DM, dry matter) were fed to satiety to triplicate groups of 20 fish (7.71 g) for 6 weeks. At the end of the feeding trial, fish fed diets containing 5% and 15% lipid showed a higher growth than those fish fed with 25% lipid. Though daily feed intake (DFI) decreased with increasing dietary lipid, there was no significant difference in daily energy intake (DEI) among treatments. As dietary lipid level increased, energy retention (EI), daily energy gain (DEG), daily lipid intake (DLI), daily lipid gain (DLG), viscerosomatic index (VSI), intraperitoneal fat ratio (IPF) and body lipid content increased dramatically and the 25% group had the highest values. Hepatosomatic index (HSI) and muscle lipid content were higher at 25% lipid group than 5% lipid group, but no significant different was found between 15% and 25% lipid group. Activities of G6PD and ME were reduced with increasing lipid intake, but activities of IDH and 6PGDH did not change among groups. In conclusion, high dietary lipid levels above 15% produced little practical benefit because of higher fat accretion in cobia.

Enzyme Activities and Alcohol Tolerance in Isofemale Lines of Drosophila melanogaster Originating from Different Habitats

Enzyme activity variation was studied in a Drosophila melanogaster population from two villages (Tiszafüred and Tiszaszolos) in Hungary. Two habitats (distillery and farmyard) were sampled in both villages and 8-9 isofemale lines were established from each sample with a total of 35 lines. The activities of ADH, alphaGPDH, IDH and 6PGDH were determined on starch gel after electrophoresis in 10 F1 females of each of the 35 isofemale lines. Three sublines were established from three selected isofemale lines of all four samples (altogether 36 sublines). Alcohol tolerance of the adult flies was assayed in these sublines. The activity of ADH was similar in the two habitats; so was the sensitivity to ethanol. Accordingly, no differences in adaptation to environmental ethanol were detected between the two habitats. The deviations between the two habitats in average activities and in the total variation of enzyme activities were not consistent in the two villages. These results suggest that founder effects and genetic drift are more pronounced in distilleries than selection. The association among enzyme activities varied greatly both between the two villages and between the two habitats. The two parameters of alcohol tolerance were not significantly different between the two habitats in any of the two villages.

Metabolic control analysis of gene-knockout Escherichia coli based on the inverse flux analysis with experimental verification

Inverse flux analysis (IFA) was utilized to investigate the effect of gene-knockout on the metabolic flux distribution of Escherichia coli. In particular, it was shown from IFA that if pyk was knocked-out, then the flux through ppc and TCA cycle pathway increased, while the acetate production flux reduced. To verify this IFA result, we cultivated pykF − E. coli and compared the fermentation data of E. coli K12. The enzyme activities of G6PDH, 6PGDH, Pgi, Pfk, Pyk, Mez, MDH, Ppc, and Pyk were also measured. Those data well coincided with the IFA result. The effects of other gene-knockout such as pgi, zwf, etc., were also investigated. From the present research, it was shown that the theoretical approach using computer shows some powers which needs careful attention.

Structure of variation in enzyme activity in natural Drosophila melanogaster populations.

Enzyme activity variation was assessed in several isofemale lines originating from two Hungarian Drosophila melanogaster populations. Samples from each population were taken from from two villages; 8-9 isofemale lines were established from each village. The activities of ADH, alphaGPDH, IDH and 6PGDH were determined in the adults (in the F1 generation) and in the larvae (in the F3 generation) as well. Enzyme activities were measured on starch gel after electrophoresis. The activity of the enzyme was detected in a single individual and it was also possible to determine its genotype. The results showed that most of the variation occurred within sites for all four enzymes. This within site variation was more or less equally partitioned into within and between isofemale line (family) components. A smaller portion of variation was attributable to the differences between the populations. Nevertheless, adult alphaGPDH, and larval IDH and 6PGDH activities exhibited significant differences between the two populations. Variation in larval activities of all enzymes was higher than that of the adults, but 6PGDH had considerably higher variation in the adults. The greater variation in larval activities probably reflected the greater environmental variation in the microhabitat of the larvae compared to that of the adults. Larval activities of the investigated enzymes showed much stronger correlation than adult activities. The correlation pattern in the adults differed greatly between the two populations.

Changes in activity of glucose-6-phosphate and 6-phosphogluconate dehydrogenase isozymes upon potato virus Y infection in tobacco leaf tissues and protoplasts

The changes in the activity of glucose-6-phosphate dehydrogenase (G6PDH) (EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (6PGDH) (EC 1.1.1.44) in leaf tissues and the subcellular localisation of their isozymes in protoplasts derived from healthy and potato virus Y (PVY) infected plants of Nicotiana tabacum L. cv. Samsun were determined. The activities of G6PDH and 6PGDH were markedly increased in virus-infected leaves during the acute phase of infection both in crude homogenate and partial purificate (when compared with the values found in healthy control plants) and correlated with the multiplication curve of PVY. Intact chloroplasts and soluble cytosolic proteins were obtained from whole plants upon the culmination of the multiplication curve of PVY and upon the enhancement of the activity of both dehydrogenases by means of differential centrifugation of broken protoplasts. The chloroplastic fraction from infected protoplasts (based on chlorophyll content or NADP +-triosephosphate dehydrogenase activity) showed an enhanced activity of G6PDH (1.81 times that of healthy protoplasts), and 6PGDH (1.77 times). Cytosol from infected protoplasts (based on phosphoenolpyruvate carboxylase activity) contained only slightly enhanced activities of G6PDH and 6PGDH (only 1.26 and 1.16 times, respectively).

Identification of an endogenous NADPH-regenerating system coupled to nitrate reduction in vitro in plant and fungal crude extracts

A low molecular weight factor obtained from the crude extract of nit-1 mutant of Neurospora crassa (NEF) was capable of stimulating the activity of reconstituted NADPH specific nitrate reductase (NR, EC 1.6.6.3; Z.Z. Alikulov, N.A. Savidov, H.S. Lips, A low molecular weight regulator of nitrate reductase in higher plants. 4th International Symposium on Inorganic Nitrogen Assimilation and 1st Fohs Biostress Symposium. Seeheim/Darmstadt, Germany, 1995, p. 9). This factor eluted from a G15 column as glucose-6-phosphate (G6P) and fructose-6-phosphate (F6P). Like the hexose-phosphates, NEF allowed rapid regeneration of NADPH from the NADP +, resulting from nitrate reduction. Sequential treatment of the NEF-containing fraction with commercial preparations of glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49), 6-phosphogluconate dehydrogenase (6PGDH, EC 1.1.1.43) and phosphoglucose isomerase (PGI, EC 5.3.1.9) resulted in the oxidation of NEF and the reduction of NADP +. NEF, therefore, was a substrate of G6PDH and 6PGDH in a reaction which reduced NADP + to NADPH. It was concluded that the low molecular weight factor enhancing NR activity isolated from fungal and plant crude extracts (Z.Z. Alikulov, N.A. Savidov, H.S. Lips, A low molecular weight regulator of nitrate reductase in higher plants. 4th International Symposium on Inorganic Nitrogen Assimilation and 1st Fohs Biostress Symposium. Seeheim/Darmstadt, Germany, 1995, p. 9) may be a mixture of hexose phosphates. G6PDH, 6PGDH and PGI were active in crude extracts of plants and fungi used for NR assays. Oxidation of one mole of G6P led to the production of approximately two moles of NADPH. The activities of PGI, G6PDH and 6PGDH exceeded that of NR in both fungal and plant crude extract. Fungal crude extracts exhibited a considerably higher capacity to regenerate NADPH than plant extracts. The addition of G6P during the in vitro NR assay increased the stability of the reaction allowing detection of very low NR activity levels. The stimulation of NR in vitro by NADPH generating systems points out the physiological importance of these systems in nitrate assimilation and in the nitrate reduction assays in situ and in vivo.

Aluminum resistance in wheat (Triticum aestivum) is associated with rapid, Al‐induced changes in activities of glucose‐6‐phosphate dehydrogenase and 6‐phosphogluconate dehydrogenase in root apices

We have investigated the effect of aluminum (Al) on the activity of glucose‐6‐phosphate dehydrogenase (G6PDH; EC 1.1.1.49) and 6‐phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44) isolated from 5‐mm root apices of 4‐day‐old wheat (Triticum aestivum) cultivars differing in resistance to Al. Rapid increases in G6PDH and 6PGDH activities were observed in Al‐resistant cultivars (PT741 and Atlas 66) during the first 10 h of treatment with 100 μM Al, while no change in the activity of either enzyme was observed in Al‐sensitive cultivars (Katepwa and Neepawa) during a 24‐h exposure to Al. The Al‐induced increases in enzyme activities observed in the Al‐resistant PT741 appear to reflect an induction of protein synthesis since the increases were completely abolished by 1 mM cycloheximide. No differences in G6PDH and 6PGDH activities were observed between the Al‐sensitive and the Al‐resistant genotypes when Al was supplied in vitro. Under these conditions, an increase in Al concentration from 0 to 1.4 mM caused a gradual decrease in activity of both enzymes, irrespective of the Al‐resistance of whole seedlings. Aluminum‐sensitive and aluminum‐resistant cultivars also differed in the rate and extent of accumulation of slowly‐exchanging Al in 5‐mm root apices. During the first 6 h of Al treatment, Al accumulation was only 10% more rapid in Katepwa than in PT741. After 24‐h exposure, accumulation in the Al‐sensitive Katepwa, was two‐fold higher. A decline in Al accumulation in a slowly‐exchanging compartment as well as a decrease in activities of G6PDH and 6PGDH were found in the Al‐resistant PT741, when seedlings were transferred to Al‐free treatment solutions after 16‐h exposure to 100 μM Al. These results suggest that rapid induction of G6PDH and 6PGDH in the Al‐resistant line PT741 by Al may play a role in the mechanism of Al resistance, possibly by regulation of the pentose phosphate pathway.

Zinc deficiency and activities of lipogenic and glycolytic enzymes in liver of rats fed coconut oil or linseed oil

In previous studies, zinc-deficient rats force-fed a diet with coconut oil as the major dietary fat developed a fatty liver, whereas zinc-deficient rats force-fed a diet with linseed oil did not. The present study was conducted to elucidate the reason for this phenomenon. In a bifactorial experiment, rats were fed zinc-adequate or zinc-deficient diets containing either a mixture of coconut oil (70 g/kg) and safflower oil (10 g/kg) ("coconut oil diet") or linseed oil (80 g/kg) ("linseed oil diet") as a source of dietary fat, and activities of lipogenic and glycolytic enzymes in liver were determined. In order to ensure adequate food intake, all the rats were force-fed. Zinc-deficient rats on the coconut oil diet developed a fatty liver, characterized by elevated levels of triglycerides with saturated and monounsaturated fatty acids. These rats also had markedly elevated activities of the lipogenic enzymes acetyl-CoA carboxylase, fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), and citrate cleavage enzyme, whereas activities of malic enzyme and glycolytic enzymes were not different compared with zinc-adequate rats on the coconut oil diet. In contrast, rats receiving the linseed oil diet had similar triglyceride concentrations regardless of zinc status, and activities of lipogenic enzymes and glycolytic enzymes were not different between the two groups. Zinc-deficient rats fed either type of dietary fat exhibited statistically significant correlations between activities of FAS, G6PDH, 6PGDH and concentrations of saturated and monounsaturated fatty acids in liver.(ABSTRACT TRUNCATED AT 250 WORDS)