Purification and characterization of xylitol dehydrogenase with L-arabitol dehydrogenase activity from the newly isolated pentose-fermenting yeast Meyerozyma caribbica 5XY2

Meyerozyma caribbica strain 5XY2, which was isolated from an alcohol fermentation starter in Thailand, was found to catabolize L-arabinose as well as a-glucose and D-xylose. The highest production amounts of ethanol from D-glucose, xylitol from D-xylose, and L-arabitol from L-arabinose were 0.45 g/g D-glucose, 0.60 g/g D-xylose, and 0.61 g/g L-arabinose with 21.7 g/L ethanol, 20.2 xylitol, and 303 g/1 L-arabitol, respectively. The enzyme with L-arabitol dehydrogenase (LAD) activity was purified from the strain and found to exhibit broad specificity to polyols, such as xylitol, D-sorbitol, ribitol, and L-arabitol. Xylitol was the preferred substrate with K-m = 16.1 mM and k(cat)/K-m = 67.0 min(-1)mM(-1), while L-arabitol was also a substrate for the enzyme with K-m = 31.1 mM and k(cat)/K-m = 6.5 min(-1) mM(-1). Therefore, this enzyme from M. caribbica was named xylitol dehydrogenase (McXDH). McXDH had an optimum temperature and pH at 40 degrees C and 9.5, respectively. The McXDH gene included a coding sequence of 1086 bp encoding a putative 362 amino acid protein of 39 kDa with an apparent homopentamer structure. Native McXDH and recombinant McXDH exhibited relative activities toward L-arabitol of approximately 20% that toward xylitol, suggesting the applicability of this enzyme with the functions of XDH and LAD to the development of pentose-fermenting Saccharomyces cerevisiae. (C) 2016, The Society for Biotechnology, Japan. All rights reserved.