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Appl Biochem Biotechnol (2015) 175:387399
DOI 10.1007/s12010-014-1269-4
I. S. M. Rafiqul & A. M. M. Sakinah
Received: 15 April 2014 /Accepted: 23 September 2014 /
Published online: 10 October 2014# Springer Science+Business Media New York 2014
Abstract Xylose reductase (XR) is an intracellular enzyme, which catalyzes xylose to xylitol conversion in the microbes. It has potential biotechnological applications in the manufacture of various commercially important specialty bioproducts including xylitol. This study aimed to prepare XR from adapted strain of Candida tropicalis and to characterize it. The XR was isolated from adapted C. tropicalis, cultivated on Meranti wood sawdust hemicellulosic hydrolysate (MWSHH)-based medium, via ultrasonication, and was characterized based on enzyme activity, stability, and kinetic parameters. It was specific to NADPH with an activity of11.16 U/mL. The enzyme was stable at pH 57 and temperature of 2540 C for 24 h and retained above 95 % of its original activity after 4 months of storage at 80 C. The Km of XR for xylose and NADPH were 81.78 mM and 7.29 M while the Vmax for them were 178.57
and 12.5 M/min, respectively. The high Vmax and low Km values of XR for xylose reflect a highly productive reaction among XR and xylose. MWSHH can be a promising xylose source for XR preparation from yeast.
Keywords Xylose reductase (XR) . Xylose . Xylitol . Meranti wood sawdust (MWS) . Hemicellulosic hydrolysate . Adapted Candida tropicalis
Introduction
Xylose reductase (XR) is a member of the aldose reductase family (EC 1.1.1.21) of enzymes and is an oxidoreductase enzyme generally found in yeast and fungi. This intracellular enzyme occurs in the cytoplasm of xylose-assimilating microbes, where it mediates the first step of xylose metabolism by reducing xylose to xylitol with the concomitant oxidation of NAD(P)H [1, 2]. XR has widespread applications in the bio-based production of ethanol, xylitol, and sorbitol from xylose [3, 4], which make the enzyme a focus of interest. The use of high-priced commercial xylose limits the large-scale production of XR as well as its industrial application for manufacturing xylitol and other value-added bioproducts. This issue has encouraged the authors to work toward the development of improved techniques to lower the costs of XR
I. S. M. Rafiqul : A. M. M. Sakinah (*)
Faculty of...