School of Life Science, University of Science and Technology of China, Hefei, Anhui 230027, People's Republic of China.
J Ind Microbiol Biotechnol. 2011 Dec;38(12):2001-10. doi: 10.1007/s10295-011-0990-z. Epub 2011 Jun 4.
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.
马克斯克鲁维酵母是一种耐热酵母，能够利用更广泛的底物，并且比大多数其他酵母物种具有更高的耐热性。马克斯克鲁维酵母可以同化木糖，但它在缺氧环境中从木糖生产乙醇的能力很差。在本研究中，克隆了马克斯克鲁维酵母木糖还原酶（KmXR）基因（Kmxyl1），并对重组酶进行了表征，以阐明限制马克斯克鲁维酵母 NBRC1777 中木糖发酵的因素。KmXR 是马克斯克鲁维酵母木糖代谢的关键酶，这通过敲除 Kmxyl1 基因得到了验证。重组 KmXR 对 NADPH 的 Km 为 65.67 μM，KmXR 活性为 1.295 U/mg，低于大多数报道的酵母 XRs，并且该酶与辅酶 NADH 没有活性。这一结果表明，来自马克斯克鲁维酵母的 XR 对辅酶具有高度特异性；结合 NADP+ 下马克斯克鲁维酵母极低的 XDH 活性，厌氧条件下的氧化还原失衡和低 KmXR 活性是导致木糖发酵受限的原因。
