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Preliminary Characterization of Xylose Reductase Partially Purified by Reversed Micelles from <i>Candida tropicalis</i> IEC5-ITV, an Indigenous Xylitol-Producing Strain

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Author(s): Micloth López del Castillo-Lozano | MaGuadalupe Aguilar-Uscanga | Yolanda Cocotle-Ronzon | Marisol Zendejas-Zaldo

Journal: Advances in Molecular Imaging
ISSN 2161-6728

Volume: 02;
Issue: 01;
Start page: 9;
Date: 2011;
Original page

Keywords: Xylose Reductase | Xylitol | Reversed Micelles | &lt | i&gt | Candida Tropicalis&lt | /i&gt

ABSTRACT
Xylose reductase (EC 1.1.1.21) of Candida tropicalis IEC5-ITV, an indigenous xylitol-producing strain, was partially purified by reversed micelles and characterized, an 8.1 fold purification factor being obtained. The XR present in the crude extract exhibited its highest specific activity at pH 6.0 and 40°C, while in that obtained by reverse micelles, this occurs at pH 6.0 and 30°C. XR before and after extraction is stable within a range of 30 to 40°C, pH 7 after one hour of incubation under these conditions. After two months’storage at –18°C, the enzyme obtained by reverse micelles lost 76.60% specific activity. The estimated molecular weight by PAGE-SDS was 32.42 kD. KM for xylose was higher for the XR extracted by reverse micelles (0.026 M) than that obtained for the enzyme before extraction (0.0059 M), while KM for cofactor NADPH was lower after than before extraction (1.85 mM to 12.0 mM respectively). There was no activity with NADH as a cofactor. Variations in pH and temperature optima, as well as kinetic parameters before and after partial XR purification by reverse micelles are probably due to an alteration in enzyme molecule structure caused by the solvents used during extraction.
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