Effect of temperature on the activities of glucose-6-phosphate dehydrogenase and hexokinase in entomopathogenic nematodes (Nematoda: Steinernematidae)

Genomic characterization, kinetics, and pathways of sulfamethazine biodegradation by Paenarthrobacter sp. A01

Biodegradation is an important route for the removal of sulfamethazine (SMZ), one of the most commonly used sulfonamide antibiotics, in the environment. However, little information is known about the kinetics, products, and pathways of SMZ biodegradation owing to the complexity of its enzyme-based biotransformation processes. In this study, the SMZ-degrading strain A01 belonging to the genus Paenarthrobacter was isolated from SMZ-enriched activated sludge reactors. The bacterial cells were rod-shaped with transient branches 2.50-4.00 μm in length with most forming in a V-shaped arrangement. The genome size of Paenarthrobacter sp. A01 had a total length of 4,885,005 bp with a GC content of 63.5%, and it contained 104 contigs and 55 RNAs. The effects of pH, temperature, initial substrate concentration and additional carbon source on the biodegradation of SMZ were investigated. The results indicated that pH 6.0-7.8, 25 °C and the addition of 0.2 g/L sodium acetate favored the biodegradation, whereas a high concentration of SMZ, 500 mg/L, had an inhibitory effect. The biodegradation kinetics with SMZ as the sole carbon source or 0.2 g/L sodium acetate as the co-substrate fit the modified Gompertz model well with a correlation coefficient (R²) of 0.99. Three biodegradation pathways were proposed involving nine biodegradation products, among which C₆H₉N₃O₂S and C₁₂H₁₂N₂ were two novel biodegradation products that have not been reported previously. Approximately 90.7% of SMZ was transformed to 2-amino-4, 6-dimethylpyrimidine. Furthermore, sad genes responsible for catabolizing sulfonamides were characterized in A01 with high similarities of 96.0%-100.0%. This study will fill the knowledge gap in the biodegradation of this ubiquitous micropollutant in the aquatic environment.

Effects of toxic β-glucosides on carbohydrate metabolism in cotton bollworm, Helicoverpa armigera (Hübner)

The purpose of this study was to evaluate the effects of three toxic β-glucosides, phlorizin, santonin, and amygdalin, on carbohydrate metabolism in the cotton bollworm, Helicoverpa armigera (Hübner), when diets mixed with β-glucosides were fed to third-instar larvae. The growth of the larvae was significantly inhibited by exposure to santonin after 96 hr but not obviously affected by phlorizin and amygdalin. The midgut trehalase activities were only 51.7%, 32%, and 42.5% of that of the control after treatment with phlorizin, santonin and amygdalin at 2 mg/ml, respectively. In the hemolymph and fat body, the amount of trehalose decreased in all cases. However, the effects of santonin on the alteration of the glycogen and glucose levels as well as the activities of glycogen phosphorylase, were different than those of the other two β-glucosides. It appears that the three β-glucosides have different influences on the carbohydrate metabolism of cotton bollworm.

Biochemical characterization of buffalo liver glucose-6-phosphate dehydrogenase isoforms

Glucose-6-phosphate dehydrogenase (G6PD) is a key regulatory enzyme involved in the pentose phosphate pathway. This works represents purification of two buffalo liver glucose-6-phosphate dehydrogenases (BLG6PD1 and BLG6PD2) using combination of ammonium sulfate precipitation and several chromatographic columns. Both enzymes (BLG6PD1 and BLG6PD2) were homogenous on both native PAGE as well as 12% SDS PAGE with molecular weights of 28 and 66 kDa. The molecular weight of BLG6PD1 and BLG6PD2 native forms were determined to be 28 and 66 kDa by gel filtration; indicating monomeric proteins. The K(m) values for BLG6PD1 and BLG6PD2 estimated to be 0.059 and 0.06 mM of β-nicotinamide adenine dinucleotide phosphate. The optimum activity of BLG6PD1 and BLG6PD2 were displayed at pH 8.0 and 8.2 with an isoelectric point (pI) of pH 7.7-7.9 and 5.7-5.9. The divalent cations MgCl2, and CoCl2 act as activators, on the other hand, FeCl2, CuCl2 and ZnCl2 are potent inhibitors of BLG6PD1 and BLG6PD2 activity. NADPH inhibited both isoenzymes competitively with Ki values of 0.012 and 0.030 mM. This study describes a reproducible purification scheme of G6PD from the liver of buffalo as a rich source.

Purification and characterization of glucose-6-phosphate dehydrogenase from camel liver

Glucose-6-phosphate dehydrogenase from camel liver was purified to homogeneity by ammonium sulfate precipitation and a combination of DEAE-cellulose, Sephacryl S-300 gel filtration, and 2', 5' ADP Sepharose 4B affinity chromatography columns. The specific activity of camel liver G6PD is increased to 1.80438 units/mg proteins with 63-fold purification. It turned out to be homogenous on both native PAGE and 12% SDS PAGE, with a molecular weight of 64 kDa. The molecular weight of the native form of camel liver G6PD was determined to be 194 kDa by gel filtration indicating a trimeric protein. The K m value was found to be 0.081 mM of NADP(+). Camel liver G6PD displayed its optimum activity at pH 7.8 with an isoelectric point (pI) of pH 6.6-6.8. The divalent cations MgCl2, MnCl2, and CoCl2 act as activators; on the other hand, CaCl2 and NiCl2 act as moderate inhibitors, while FeCl2, CuCl2, and ZnCl2 are potent inhibitors of camel liver G6PD activity. NADPH inhibited camel liver G6PD competitively with K i value of 0.035 mM. One binding site was deduced for NADPH on the enzyme molecule. This study presents a simple and reproducible purification procedure of G6PD from the camel liver.

Cold-adapted enzymes

By far the largest proportion of the Earth's biosphere is comprised of organisms that thrive in cold environments (psychrophiles). Their ability to proliferate in the cold is predicated on a capacity to synthesize cold-adapted enzymes. These enzymes have evolved a range of structural features that confer a high level of flexibility compared to thermostable homologs. High flexibility, particularly around the active site, is translated into low-activation enthalpy, low-substrate affinity, and high specific activity at low temperatures. High flexibility is also accompanied by a trade-off in stability, resulting in heat lability and, in the few cases studied, cold lability. This review addresses the structure, function, and stability of cold-adapted enzymes, highlighting the challenges for immediate and future consideration. Because of the unique properties of cold-adapted enzymes, they are not only an important focus in extremophile biology, but also represent a valuable model for fundamental research into protein folding and catalysis.

Purification and kinetics of sheep kidney cortex glucose-6-phosphate dehydrogenase

Glucose-6-phosphate dehydrogenase (G-6-PD) is one of the important enzymes, which is responsible for the production of NADPH and ribose-5-phosphate. NADPH is used for the biosynthetic reactions and protection of the cells from free radicals. We have investigated some properties and kinetic mechanism of the sheep kidney cortex G-6-PD. This enzyme has been purified 1,384-fold with a yield of 16.96% and had a specific activity of 27.69 U/mg protein. The purification procedure consists of 2', 5'-ADP-Sepharose 4B affinity chromatography after ultracentrifugation. The sheep kidney cortex G-6-PD was found to operate according to a Ping Pong Bi Bi mechanism. The kinetic parameters from sheep K(m) values for G-6-P and NADP(+) and V(m) were determined to be 0.041+/-0.0043 mM, 0.0147+/-0.001 mM and 28.23+/-0.86 microMol min(-1) mg protein(-1), respectively. The pH optimum was 7.4 and the optimum temperature was 45 degrees C. In our previous study we have found that lamb kidney cortex G-6-PD enzyme obeys 'Ordered Bi Bi' mechanism. We suggest that kinetic mechanism altered due to the aging since sheep G-6-PD uses a 'ping pong' mechanism.

Some like it cold: biocatalysis at low temperatures

In the last few years, increased attention has been focused on a class of organisms called psychrophiles. These organisms, hosts of permanently cold habitats, often display metabolic fluxes more or less comparable to those exhibited by mesophilic organisms at moderate temperatures. Psychrophiles have evolved by producing, among other peculiarities, "cold-adapted" enzymes which have the properties to cope with the reduction of chemical reaction rates induced by low temperatures. Thermal compensation in these enzymes is reached, in most cases, through a high catalytic efficiency associated, however, with a low thermal stability. Thanks to recent advances provided by X-ray crystallography, structure modelling, protein engineering and biophysical studies, the adaptation strategies are beginning to be understood. The emerging picture suggests that psychrophilic enzymes are characterized by an improved flexibility of the structural components involved in the catalytic cycle, whereas other protein regions, if not implicated in catalysis, may be even more rigid than their mesophilic counterparts. Due to their attractive properties, i.e., a high specific activity and a low thermal stability, these enzymes constitute a tremendous potential for fundamental research and biotechnological applications.

Adjustments of the enzymatic complement for polyol biosynthesis and accumulation in diapausing cold-acclimated adults of Pyrrhocoris apterus

The capacity to accumulate winter polyols (mainly ribitol and sorbitol) during cold-acclimation in Pyrrhocoris apterus is restricted only to the adults that have previously entered diapause. The enzymatic complement involved in polyol biosynthesis was found to differ in a complex manner between diapause and non-diapause adults. Nearly 100% of glycogen phosphorylase (GPase) was present in its active form in non-diapause adults irrespective of their acclimation status. In contrast, less than 40% of GPase was present in its active form in diapause adults prior to cold-acclimation and the inactive form was rapidly activated upon transition from 5 to 0 degrees C, concomitantly with the start of rapid polyol accumulation. The flow of carbon released by activation of glycogen degradation might be routed to the pentose cycle because the activity of glucose-6-P dehydrogenase (G(6)P-DH) was significantly higher and it increased with cold-acclimation in diapause adults while it was relatively low and it decreased with cold-acclimation in non-diapause adults. Reducing equivalents in the form of NADPH, which were generated in the pentose cycle, might require re-oxidation. Such re-oxidation might be achieved during reduction of sugars to polyols. The activity of NADP(H)-dependent aldose reductase (AR) was about 20-fold higher in diapause than in non-diapause adults. Similarly, the activity of NAD(H)-dependent polyol dehydrogenase (PDH) was higher in diapause adults. In addition, we found a very high activity of an unusual enzyme, NADP(H)-dependent ketose reductase (KR), exclusively in diapause adults. KR might be involved in reduction of fructose to sorbitol. Although its affinity for fructose as a substrate was low (K(M)=0.64M), its activity was about 10-fold higher than that of PDH with fructose. Moreover, the activity of KR significantly increased with cold-acclimation while that of PDH remained unchanged. Different electrophoretic mobilities in PAGE gel suggested that KR and PDH are two different enzymes with specific requirement for NADP(H) or NAD(H), respectively, as co-factors.

The effect of temperature on the fatty acids and isozymes of a psychrotrophic and two mesophilic species of Xenorhabdus, a bacterial symbiont of entomopathogenic nematodes

In the first part of this study, generation times relative to temperature, together with cardinal and conceptual temperatures, were determined for four strains of Xenorhabdus bacteria that represented three geographically distinct species. The data showed that the NF strain of Xenorhabdus bovienii, like the Umeå strain of the same species, is psychrotrophic, while Xenorhabdus sp. TX strain resembles Xenorhabdus nematophila All strain in being mesophilic. In the second part, the capacity of these bacteria to adapt to changes in temperature, shown by changes in fatty acid composition, was investigated. As temperature declined, the proportions of the two major unsaturated fatty acids, palmitoleic (16:1omega7) acid and oleic (18:1omega9) acid, increased significantly in all of the strains. The proportion of the prevalent saturated fatty acid, which was palmitic acid (16:0), decreased. In the All, NF, and Umeå strains, myristic acid (14:0), margaric acid (17:0), cyclopropane (17:0c), and arachidic acid (20:0) decreased with decreasing temperature. In the third part of the study, the synthesis of isozymes in response to changing temperature was investigated. For the seven enzymes studied, the numbers for which isozyme synthesis was temperature related were as follows: five for Umeå, four for All, three for NF, and two for TX. Where the study dealt with fatty acid composition and isozyme synthesis, the results show a broad capacity for physiological temperature adaptation among strains of different climatic origin.