title: Optimal activity and thermostability of xylose reductase from Debaryomyces hansenii UFV-170.
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 degrees C, respectively, was evaluated by a 2(2) 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 degrees C, which were fairly confirmed by additional tests performed under these conditions. The enzyme proved very stable at low temperature (4 degrees C), keeping its activity almost entirely after 360 min, which corresponded to the half-time at 39 degrees C. On the other hand, at temperatures >or=50 degrees C it was lost almost completely after only 20 min.
authors.affiliation: Department of Food Technology, Federal University of Viçosa, Av. P. H. Rolfs s/n, Viçosa, Minas Gerais, 36571-000, Brazil.
authors.forename: Fábio C
authors.initials: FC
authors.lastname: Sampaio
authors.forename: Janaína T
authors.initials: JT
authors.lastname: de Faria
authors.forename: Flávia M Lopes
authors.initials: FM
authors.lastname: Passos
authors.forename: Attilio
authors.initials: A
authors.lastname: Converti
authors.forename: Luis Antônio
authors.initials: LA
authors.lastname: Minin
mesh_terms: D000449:Aldehyde Reductase / Q000378:metabolism*; D003470:Culture Media; D004795:Enzyme Stability; D005516:Food Microbiology; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007218:Industrial Microbiology; D007700:Kinetics; D004718:Saccharomycetales / Q000201:enzymology* / Q000254:growth & development; D013696:Temperature; D014994:Xylose / Q000378:metabolism
chemical_list: D003470:Culture Media; D014994:Xylose; D000449:Aldehyde Reductase