Preliminary Kinetic Characterization of Xylose Reductase and Xylitol Dehydrogenase Extracted from Candida guilliermondii FTI 20037 Cultivated in Sugarcane Bagasse Hydrolysate for Xylitol Production

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Abstract
Candida guilliermondii FTI 20037 was cultured in sugarcane bagasse hydrolysate supplemented with 2.0 g/L of (NH4)2SO4, 0.1 g/L of CaCl2·2H2O, and 20.0 g/L of rice bran at 35°C; pH 4.0; agitation of 300 rpm; and aeration of 0.4, 0.6, or 0.8 vvm. The high xylitol production (20.0 g/L) and xylose reductase (XR) activity (658.8 U/mg of protein) occurred at an aeration of 0.4 vvm. Under this condition, the xylitol dehydrogenase (XD) activity was low. The apparent K M for XR and XD against substrates and cofactors were as follows: for XR, 6.4×10−2 M (xylose) and 9.5×10−3 mM (NADPH); for XD, 1.6×10−1 M (xylitol) and 9.9×10−2 mM (NAD+). Because XR requires about 10-fold less xylose and cofactor than XD for the condition in which the reaction rate is half of the V max, some interference on the overall xylitol production by the yeast could be expected.

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