title: Identification of a xylose reductase gene in the xylose metabolic pathway of Kluyveromyces marxianus NBRC1777.
abstract: Kluyveromyces marxianus is thermotolerant yeast that is able to utilize a wider range of substrates and has greater thermal tolerance than most other yeast species. K. marxianus can assimilate xylose, but its ability to produce ethanol from xylose in oxygen-limited environments is poor. In the present study, the K. marxianus xylose reductase (KmXR) gene (Kmxyl1) was cloned and the recombinant enzyme was characterized to clarify the factors that limit xylose fermentation in K. marxianus NBRC1777. KmXR is a key enzyme in the xylose metabolism of K. marxianus, which was verified by disruption of the Kmxyl1 gene. The Km of the recombinant KmXR for NADPH is 65.67 μM and KmXR activity is 1.295 U/mg, which is lower than those of most reported yeast XRs, and the enzyme has no activity with coenzyme NADH. This result demonstrates that the XR from K. marxianus is highly coenzyme specific; combined with the extremely low XDH activity of K. marxianus with NADP+, the limitation of xylose fermentation is due to a redox imbalance under anaerobic conditions and low KmXR activity.
authors.affiliation: School of Life Science, University of Science and Technology of China, Hefei, Anhui 230027, People's Republic of China.
authors.forename: Biao
authors.initials: B
authors.lastname: Zhang
authors.forename: Ling
authors.initials: L
authors.lastname: Zhang
authors.forename: Dongmei
authors.initials: D
authors.lastname: Wang
authors.forename: Xiaolian
authors.initials: X
authors.lastname: Gao
authors.forename: Jiong
authors.initials: J
authors.lastname: Hong
mesh_terms: D000449:Aldehyde Reductase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D003067:Coenzymes / Q000378:metabolism; D005285:Fermentation; D007716:Kluyveromyces / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D014994:Xylose / Q000378:metabolism*
chemical_list: D003067:Coenzymes; D009243:NAD; D009249:NADP; D014994:Xylose; D000449:Aldehyde Reductase