Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.5.2 (NQO1)
 6,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Monodehydroascorbate reductase (EC 1.6.5.4) was purified from cucumber fruit to a homogeneous state as judged by polyacrylamide gel electrophoresis. The cucumber monodehydroascorbate reductase was a monomer with a molecular weight of 47,000. It contained 1 mol of FAD/mol of enzyme which was reduced by NAD(P)H and reoxidized by monodehydroascorbate. The enzyme had an exposed thiol group whose blockage with thiol reagents inhibited the electron transfer from NAD(P)H to the enzyme FAD. Both NADH and NADPH served as electron donors with Km values of 4.6 and 23 microM, respectively, and Vmax of 200 mol of NADH and 150 mol of NADPH oxidized mol of enzyme-1 s-1. The Km for monodehydroascorbate was 1.4 microM. The amino acid composition of the enzyme is presented. In addition to monodehydroascorbate, the enzyme catalyzed the reduction of ferricyanide and 2,6-dichloroindophenol but showed little reactivity with calf liver cytochrome b5 and horse heart cytochrome c. The kinetic data suggested a ping-pong mechanism for the monodehydroascorbate reductase-catalyzed reaction. Cucumber monodehydroascorbate reductase occurs in soluble form and can be distinguished from NADPH dehydrogenase, NADH dehydrogenase, DT diaphorase, microsome-bound NADH-cytochrome b5 reductase, and NADPH-cytochrome c reductase by its molecular weight, amino acid composition, and specificity of electron acceptors and donors.
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PMID:Monodehydroascorbate reductase from cucumber is a flavin adenine dinucleotide enzyme. 405 27

We have used a model of dietary deficiency that leads to a chronic oxidative stress to evaluate responses that are adaptations invoked to boost cellular defense systems. Long-Evans hooded rats were fed with a diet lacking vitamin E (E) and selenium (Se) for 7 wk from weaning leading to animals deficient in both nutrients (-E -Se). In the absence of an electron donor, liver plasma membranes from these rats were more sensitive to lipid peroxidation, although they contained 40% greater amounts of ubiquinone than the plasma membranes from rats consuming diets with sufficient vitamin E and Se (+E +Se). The incubation of plasma membranes with NAD(P)H resulted in protection against peroxidation, and this effect was more pronounced in -E -Se membranes. Deficiency was accompanied by a twofold increase in redox activities associated with trans plasma membrane electron transport such as ubiquinone reductase and ascorbate free radical reductase. Staining with a polyclonal antibody against pig liver cytochrome b5 reductase, which acts as one ubiquinone reductase in the plasma membrane, showed an increased expression of the enzyme in membranes from -E -Se rats. Little DT-diaphorase activity was measured in +E +Se plasma membranes, but this activity was dramatically increased in -E -Se plasma membranes. No such increase was found in liver cytosols, which contained elevated activity of calcium-independent phospholipase A2. Thus, ubiquinone-dependent antioxidant protection in +E +Se plasma membranes is based primarily on NADH-cytochrome b5 reductase, whereas additional protection needed in -E -Se plasma membranes is supported by the increase of ubiquinone levels, increased expression of the cytochrome b5 reductase, and translocation of soluble DT-diaphorase to the plasma membrane. Our results indicate that, in the absence of vitamin E and Se, enhancement of ubiquinone-dependent reductase systems can fulfill the membrane antioxidant protection.
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PMID:Vitamin E and selenium deficiency induces expression of the ubiquinone-dependent antioxidant system at the plasma membrane. 983 56