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Substrate Tolerance (substrate + tolerance)
Selected AbstractsProperties of pyranose dehydrogenase purified from the litter-degrading fungus Agaricus xanthodermaFEBS JOURNAL, Issue 3 2007Magdalena Kujawa We purified an extracellular pyranose dehydrogenase (PDH) from the basidiomycete fungus Agaricus xanthoderma using ammonium sulfate fractionation and ion-exchange and hydrophobic interaction chromatography. The native enzyme is a monomeric glycoprotein (5% carbohydrate) containing a covalently bound FAD as its prosthetic group. The PDH polypeptide consists of 575 amino acids and has a molecular mass of 65 400 Da as determined by MALDI MS. On the basis of the primary structure of the mature protein, PDH is a member of the glucose,methanol,choline oxidoreductase family. We constructed a homology model of PDH using the 3D structure of glucose oxidase from Aspergillus niger as a template. This model suggests a novel type of bi-covalent flavinylation in PDH, 9- S -cysteinyl, 8-,- N3-histidyl FAD. The enzyme exhibits a broad sugar substrate tolerance, oxidizing structurally different aldopyranoses including monosaccharides and oligosaccharides as well as glycosides. Its preferred electron donor substrates are d -glucose, d -galactose, l -arabinose, and d -xylose. As shown by in situ NMR analysis, d -glucose and d -galactose are both oxidized at positions C2 and C3, yielding the corresponding didehydroaldoses (diketoaldoses) as the final reaction products. PDH shows no detectable activity with oxygen, and its reactivity towards electron acceptors is rather limited, reducing various substituted benzoquinones and complexed metal ions. The azino-bis-(3-ethylbenzthiazolin-6-sulfonic acid) cation radical and the ferricenium ion are the best electron acceptors, as judged by the catalytic efficiencies (kcat/Km). The enzyme may play a role in lignocellulose degradation. [source] The Substrate Spectra of Pentaerythritol Tetranitrate Reductase, Morphinone Reductase, N -Ethylmaleimide Reductase and Estrogen-Binding Protein in the Asymmetric Bioreduction of Activated AlkenesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010Nicole Abstract Four flavoproteins from the old yellow enzyme (OYE) family, pentaerythritol tetranitrate (PETNR) reductase, N -ethylmaleimide reductase (NEMR), morphinone reductase (MorR) and estrogen-binding protein (EBP1), exhibited a broad substrate tolerance by accepting conjugated enals, enones, imides, dicarboxylic acids and esters, as well as a nitroalkene and therefore can be employed for the asymmetric bioreduction of carbon-carbon double (CC) bonds. In particular, morphinone reductase and estrogen-binding protein often showed a complementary stereochemical preference in comparison to that of previously investigated OYEs. [source] Broadening the mission of an RNA enzymeJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 6 2009Michael C. Marvin Abstract The "RNA World" hypothesis suggests that life developed from RNA enzymes termed ribozymes, which carry out reactions without assistance from proteins. Ribonuclease (RNase) P is one ribozyme that appears to have adapted these origins to modern cellular life by adding protein to the RNA core in order to broaden the potential functions. This RNA-protein complex plays diverse roles in processing RNA, but its best-understood reaction is pre-tRNA maturation, resulting in mature 5' ends of tRNAs. The core catalytic activity resides in the RNA subunit of almost all RNase P enzymes but broader substrate tolerance is required for recognizing not only the diverse sequences of tRNAs, but also additional cellular RNA substrates. This broader substrate tolerance is provided by the addition of protein to the RNA core and allows RNase P to selectively recognize different RNAs, and possibly ribonucleoprotein (RNP) substrates. Thus, increased protein content correlated with evolution from bacteria to eukaryotes has further enhanced substrate potential enabling the enzyme to function in a complex cellular environment. J. Cell. Biochem. 108: 1244,1251, 2009. © 2009 Wiley-Liss, Inc. [source] Phytoremediation: The uptake of metals and metalloids by rhodes grass grown on metal-contaminated soilREMEDIATION, Issue 2 2005Scott M. Keeling An experiment was performed to examine the phytoremediation potential of Rhodes grass (Chloris gayana Kunth cv. ,Pioneer'). The study sought to determine substrate tolerance, biomass production, and plant uptake of antimony (Sb), arsenic (As), cadmium (Cd), lead (Pb), silver (Ag), and zinc (Zn). The plants were grown on weight percent mixtures (5 percent, 15 percent, 25 percent, 35 percent, 50 percent) of a vertisol soil and base-metal mine tailings (7,2,040 ,g/g As, , 30 ,g/g Cd, 30,12,000 ,g/g Pb, and 72,4,120 ,g/g Zn). The 5 percent and 15 percent amendment of mine tailings increased the biomass production of Rhodes grass (from 0.1 g/plant to , 3.5 g/plant) without appreciably elevating plant concentrations of the elements. Plant growth decreased by greater than 50 percent for the substrate containing greater than 25 percent tailings (3,023 ,g/g Pb and 1,084 ,g/g Zn). Reduced biomass production coincided with maximal Zn uptake by Rhodes grass (249.8 ,g/g), indicating tailings induced phytotoxicity. The total concentrations of metals and metalloids tolerated by Rhodes grass in the plant-growth medium indicated hypertolerance to elevated As, Pb, and Zn concentrations. Partial extraction of the plant-growth medium determined that plant-available Pb was ten times higher than Ag, As, Cd, and Zn availability. However, Rhodes grass accumulated low levels of Pb, in addition to As and Cd, over the experimental range, indicating low fodder toxicity risk to browsing livestock. This study concludes that if there are no invasive species issues associated with conservation land uses, Rhodes grass is well suited to metalliferous mined land revegetation and would therefore be highly effective for such programs in subtropical and tropical Australia. © 2005 Wiley Periodicals, Inc. [source] | ||||||||||