Purification and characterization of NADP-isocitrate dehydrogenase from skeletal muscle of Urocitellus richardsonii

NADP-dependent isocitrate dehydrogenase (NADP-IDH, EC 1.1.1.42) catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate with the concomitant production of NADPH. NADPH plays important roles in many biosynthesis pathways, maintenance of proper oxidation-reduction balance, and protection against oxidative damage. This present study investigated the dynamic nature of NADP-IDH during hibernation by purifying it from the skeletal muscle of Richardson's ground squirrel (Urocitellus richardsonii) and analyzing its structural and functional changes in response to hibernation. Kinetic parameters of purified NADP-IDH from euthermic and hibernating ground squirrel skeletal muscle were characterized at 22 °C and 5 °C. Relative to euthermic muscle, -NADP-IDH in hibernating muscle had a higher affinity for its substrate, isocitrate at 22 °C, whereas at 5 °C, there was a significant decrease in isocitrate affinity. Western blot analysis revealed greater serine and threonine phosphorylation in hibernator NADP-IDH as compared to euthermic NADP-IDH. In addition, Bioinformatic analysis predicted the presence of 18 threonine and 21 serine phosphorylation sites on squirrel NADP-IDH. The structural and functional changes in NADP-IDH indicate the ability of the organism to reduce energy consumption during hibernation, while emphasizing increased NADPH production, and thus antioxidant activity, during torpor arousal cycles.

The mitochondrial uncoupler 2,4-dinitrophenol attenuates sodium nitroprusside-induced toxicity in Drosophila melanogaster: potential involvement of free radicals

The toxicity of sodium nitroprusside (SNP) (an inducer of oxidative/nitrosative stress) and the attenuation of SNP effects by 2,4-dinitrophenol (DNP) (that induces mild uncoupling of respiration) were evaluated in the Drosophila melanogaster model system. Fly larvae were raised on food supplemented with 1.0 mM SNP, 0.5 or 1.25 mM DNP, or with mixtures 1.0 mM SNP plus 0.5 or 1.25 mM DNP. Food supplementation with SNP decreased larval viability and pupation height whereas supplementation with DNP substantially reversed these changes. Biochemical analyses of oxidative stress markers and activities of antioxidant and associated enzymes were carried out on 2-day-old flies emerged from control larvae and larvae fed on food supplemented with SNP, DNP, or SNP/DNP mixtures. Larval exposure to SNP lowered activities of aconitase, while the presence of DNP reduced the negative impact of SNP by raising aconitase activity back to near control levels. Larval treatment with SNP also elevated the contents of carbonyl protein, uric acid and low molecular mass thiols and produced higher activities of superoxide dismutase, glutathione S-transferase, glucose-6-phosphate dehydrogenase and thioredoxin reductase in adult flies. However, the presence of DNP in the food mixtures prevented SNP-induced changes in thioredoxin reductase and glucose-6-phosphate dehydrogenase activities, as well as uric acid and low-molecular-mass thiol content. The potential mechanisms by which DNP exerts protective effects against SNP toxicity are discussed.