Optimal activity and thermostability of xylose reductase from <Emphasis Type="Italic">Debaryomyces hansenii</Emphasis> UFV-170 |
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Authors: | Fábio C Sampaio Janaína T de Faria Flávia M Lopes Passos Attilio Converti Luis Antônio Minin |
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Institution: | 1.Department of Food Technology,Federal University of Vi?osa,Vi?osa,Brazil;2.Department of Microbiology,Federal University of Vi?osa,Vi?osa,Brazil;3.Department of Chemical and Process Engineering,Genoa University,Genoa,Italy |
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Abstract: | Xylose reductase (XR) is the enzyme that catalyzes the first step of xylose metabolism. Although XRs from various yeasts have
been characterized, little is known about this enzyme in Debaryomyces hansenii. In the present study, response surface analysis was used to determine the optimal conditions for D. hansenii UFV-170 XR activity. The influence of pH and temperature, ranging from 4.0 to 8.0 and from 25 to 55°C, respectively, was
evaluated by a 22 central composite design face-centered. The F-test (ANOVA) and the Student’s t test were performed to evaluate the statistical significance of the model and the regression coefficients, respectively.
The NADPH-dependent XR activity varied from 0.502 to 2.53 U mL−1, corresponding to 0.07–0.352 U mg−1, whereas the NADH-dependent one was almost negligible. The model predicted with satisfactory correlation (R
2 = 0.940) maximum volumetric activity of 2.27 U mL−1 and specific activity of 0.300 U mg−1 at pH 5.3 and 39°C, which were fairly confirmed by additional tests performed under these conditions. The enzyme proved very
stable at low temperature (4°C), keeping its activity almost entirely after 360 min, which corresponded to the half-time at
39°C. On the other hand, at temperatures ≥50°C it was lost almost completely after only 20 min. |
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Keywords: | Xylose reductase Debaryomyces hansenii Experimental design Response surface methodology Enzyme activity |
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