Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.5.4 (SOR)
 720 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Monodehydroascorbate radicals are generated in plant cells enzymatically by the hydrogen peroxide scavenging enzyme, ascorbate peroxidase, and nonenzymatically via the univalent oxidation of ascorbate by superoxide, hydroxyl, and various organic radicals. Regeneration of ascorbate is achieved by monodehydroascorbate reductase (EC 1.6.5.4) using NAD(P)H as an electron donor or, alternatively, by a set of two coupled reactions requiring dehydroascorbate reductase, glutathione reductase, glutathione, and NAD(P)H. As monodehydroascorbate reductase is a key enzyme in maintaining reduced pools of ascorbate, an important antioxidant, we undertook this study to learn more about its structure, function, and regulation. Herein we report the molecular cloning and characterization of a cDNA encoding monodehydroascorbate reductase of pea (Pisum sativum L.). The cDNA encodes a 433-amino acid polypeptide that shows, respectively, 73 and 87% identity with peptide fragments from soybean and cucumber monodehydroascorbate reductase. Monodehydroascorbate reductase contains the NAD(P)H and FAD binding domains of other flavin oxidoreductases. The cloned enzyme lacks a transit peptide, but the sequence of the carboxyl terminus is Ser-Lys-Ile, similar to the targeting motif found in peroxisomal proteins. When expressed in Escherichia coli fused to maltose-binding protein, monodehydroascorbate reductase has enzymatic properties comparable with purified soybean and cucumber monodehydroascorbate reductase. Northern blot analysis shows that the monodehydroascorbate reductase transcript is 1.6 kilobase in size and is expressed at relatively low levels in all plant tissues examined.
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PMID:Molecular cloning and characterization of a cDNA encoding pea monodehydroascorbate reductase. 798 54

The glyoxysomes of growing oilseed seedlings produce H2O2, a reactive oxygen species, during the beta-oxidation of lipids stored in the cotyledons. An expression library of dark-grown cotton (Gossypium hirsutm L.) cotyledons was screened with antibodies that recognized a 31-kD glyoxysomal membrane polypeptide. A full-length cDNA clone (1258 bp) was isolated that encodes a 32-kD subunit of ascorbate peroxidase (APX) with a single, putative membrane-spanning region near the C-terminal end of the polypeptide. Internal amino acid sequence analysis of the cotton 31-kD polypeptide verified that this clone encoded this protein. This enzyme, designated gmAPX, was immunocytochemically and enzymatically localized to the glyoxysomal membrane in cotton cotyledons. The activity of monodehydroascorbate reductase, a protein that reduces monodehydroascorbate to ascorbate with NADH, also was detected in these membranes. The co-localization of gmAPX and monodehydroascorbate reductase within the glyoxysomal membrane likely reflects an essential pathway for scavenging reactive oxygen species and also provides a mechanism to regenerate NAD+ for the continued operation of the glyoxylate cycle and beta-oxidation of fatty acids. Immunological cross-reactivity of 30- to 32-kD proteins in glyoxysomal membranes of cucumber, sunflower, castor bean, and cotton indicate that gmAPX is common among oilseed species.
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PMID:Ascorbate peroxidase. A prominent membrane protein in oilseed glyoxysomes. 874 35

The production of superoxide radicals (O2(-).) and the activities of ferricyanide reductase and cytochrome c reductase were investigated in peroxisomal membranes from pea (Pisum sativum L.) leaves using NADH and NADPH as electron donors. The generation of O2(-). by peroxisomal membranes was also assayed in native polyacrylamide gels using an in situ staining method with NitroBlue Tetrazolium (NBT). When peroxisomal membranes were assayed under native conditions using NADH or NADPH as inducer, two different O2(-).-dependent Formazan Blue bands were detected. Analysis by SDS/PAGE of these bands demonstrated that the NADH-induced NBT reduction band contained several polypeptides (PMP32, PMP61, PMP56 and PMP18, where PMP is peroxisomal membrane polypeptide and the number indicates molecular mass in kDa), while the NADPH-induced band was due exclusively to PMP29. PMP32 and PMP29 were purified by preparative SDS/PAGE and electroelution. Reconstituted PMP29 showed cytochrome c reductase activity and O2(-). production, and used NADPH specifically as electron donor. PMP32, however, had ferricyanide reductase and cytochrome c reductase activities, and was also able to generate O2(-). with NADH as electron donor, whereas NADPH was not effective as an inducer. The reductase activities of, and O2(-). production by, PMP32 were inhibited by quinacrine. Polyclonal antibodies against cucumber monodehydroascorbate reductase (MDHAR) recognized PMP32, and this polypeptide is likely to correspond to the MDHAR reported previously in pea leaf peroxisomal membranes.
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PMID:Characterization of membrane polypeptides from pea leaf peroxisomes involved in superoxide radical generation. 989 98

Coenzyme Q (Q) is an essential component of the mitochondrial respiratory chain in eukaryotic cells but also is present in other cellular membranes where it acts as an antioxidant. Because Q synthesis machinery in Saccharomyces cerevisiae is located in the mitochondria, the intracellular distribution of Q indicates the existence of intracellular Q transport. In this study, the uptake of exogenous Q(6) by yeast and its transport from the plasma membrane to mitochondria was assessed in both wild-type and in Q-less coq7 mutants derived from four distinct laboratory yeast strains. Q(6) supplementation of medium containing ethanol, a non-fermentable carbon source, rescued growth in only two of the four coq7 mutant strains. Following culture in medium containing dextrose, the added Q(6) was detected in the plasma membrane of each of four coq7 mutants tested. This detection of Q(6) in the plasma membrane was corroborated by measuring ascorbate stabilization activity, as catalyzed by NADH-ascorbate free radical reductase, a transmembrane redox activity that provides a functional assay of plasma membrane Q(6). These assays indicate that each of the four coq7 mutant strains assimilate exogenous Q(6) into the plasma membrane. The two coq7 mutant strains rescued by Q(6) supplementation for growth on ethanol contained mitochondrial Q(6) levels similar to wild type. However, the content of Q(6) in mitochondria from the non-rescued strains was only 35 and 8%, respectively, of that present in the corresponding wild-type parental strains. In yeast strains rescued by exogenous Q(6), succinate-cytochrome c reductase activity was partially restored, whereas non-rescued strains contained very low levels of activity. There was a strong correlation between mitochondrial Q(6) content, succinate-cytochrome c reductase activity, and steady state levels of the cytochrome c(1) polypeptide. These studies show that transport of extracellular Q(6) to the mitochondria operates in yeast but is strain-dependent. When Q biosynthesis is disrupted in yeast strains with defects in the intracellular transport of exogenous Q, the bc(1) complex is unstable. These results indicate that delivery of exogenous Q(6) to mitochondria is required fore activity and stability of the bc(1) complex in yeast coq mutants.
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PMID:Uptake of exogenous coenzyme Q and transport to mitochondria is required for bc1 complex stability in yeast coq mutants. 1178 8

Ascorbic acid is a ubiquitous water soluble antioxidant that plays a critical role in plant growth and environmental stress tolerance. It acts as a free radical scavenger as well as a source of reducing power for several cellular processes. Because of its pivotal role in regulating plant growth under optimal as well as sub-optimal conditions, it becomes obligatory for plants to maintain a pool of reduced ascorbic acid. Several cellular processes help in maintaining the reduced ascorbic acid pool, by regulating its synthesis and regeneration processes. Current study demonstrates that monodehydroascorbate reductase is an important enzyme responsible for maintaining the reduced ascorbate pool, by optimizing the recycling of oxidized ascorbate. Cloning and functional characterization of this important stress inducible gene is of great significance for its imperative use in plant stress management. Therefore, we have cloned and functionally validated the role of monodehydroascorbate reductase gene (mdar) from a drought tolerant variety of Eleusine coracana. The cloned Ecmdar gene comprises of 1437bp CDS, encoding a 478 amino acid long polypeptide. The active site analysis showed presence of conserved Tyr348 residue, facilitating the catalytic activity in electron transfer mechanism. qPCR expression profiling of Ecmdar under stress indicated that it is an early responsive gene. The analysis of Ecmdar overexpressing Arabidopsis transgenic lines suggests that monodehydroascorbate reductase acts as a key stress regulator by modulating the activity of antioxidant enzymes to strengthen the ROS scavenging ability and maintains ROS homeostasis. Thus, it is evident that Ecmdar is an important gene for cellular homeostasis and its over-expression could be successfully used to strengthen stress tolerance in crop plants.
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PMID:Molecular cloning, in-silico characterization and functional validation of monodehydroascorbate reductase gene in Eleusine coracana. 2917 70