NADH-LINKED ALDOSE REDUCTASE - THE KEY TO ANAEROBIC ALCOHOLIC FERMENTATION OF XYLOSE BY YEASTS
NADH-LINKED ALDOSE REDUCTASE - THE KEY TO ANAEROBIC ALCOHOLIC FERMENTATION OF XYLOSE BY YEASTS
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DOI：
10.1007/bf00251847
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发表时间：
1984-01-01
影响因子：
5
通讯作者：
SCHEFFERS, WA
中科院分区：
文献类型：
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作者：
BRUINENBERG, PM;DEBOT, PHM;SCHEFFERS, WA
在好氧和厌氧间歇培养条件下，研究了真菌念珠菌、嗜丹肿梭菌和毕赤酵母利用d -木糖的动力学和酶学。这些酵母在好氧条件下不产生乙醇。当转到厌氧时，C. utilis培养物没有木糖发酵；在P. tannophilus中，乙醇生成率明显很低；用尖柄假单胞菌快速发酵木糖。这些酵母的不同行为很可能是由木糖代谢初始步骤的性质差异所解释的：在C. utilis中，木糖通过nadph依赖的木糖还原酶和NAD+连接的木糖醇脱氢酶代谢。因此，C. utilis将木糖转化为乙醇导致NADH的过量产生，从而在缺乏氧气的情况下阻断代谢活动。然而，在褐皮假单胞菌和棘毛假单胞菌中，除了nadph连接的木糖还原酶外，还存在nadh连接的木糖还原酶。显然，木糖代谢通过NADH依赖的还原酶绕过了NAD+/NADH氧化还原系统的不平衡，从而允许在厌氧条件下将木糖发酵成乙醇。P. tannophilus和P. stipitis的木糖发酵速率与nadh连接的木糖还原酶活性相对应，符合这一假设。与各种木糖同化酵母的比较研究表明，只有具有nadh连接醛糖还原酶的生物才会发生木糖的显著酒精发酵。
The kinetics and enzymology of D-xylose utilization were studied in aerobic and anaerobic batch cultures of the facultatively fermentative yeasts Candida utilis, Pachysolen tannophilus and Pichia stipitis. These yeasts did not produce ethanol under aerobic conditions. When shifted to anaerobiosis, cultures of C. utilis did not show fermentation of xylose; in P. tannophilus a very low rate of ethanol formation was apparent; with P. stipitus rapid fermentation of xylose occurred. The different behavior of these yeasts is most probably explained by differences in the nature of the initial steps of xylose metabolism: in C. utilis xylose is metabolized via an NADPH-dependent xylose reductase and an NAD+-linked xylitol dehydrogenase. As a consequence, conversion of xylose to ethanol by C. utilis leads to an overproduction of NADH which blocks metabolic activity in the absence of O2. In P. tannophilus and P. stipitis, however, apart from an NADPH-linked xylose reductase, an NADH-linked xylose reductase was present. Appparently, xylose metabolism via the NADH-dependent reductase circumvents the imbalance of the NAD+/NADH redox system, thus allowing fermentation of xylose to ethanol under anaerobic conditions. That the rate of xylose fermentation in P. tannophilus and P. stipitis corresponds with the activity of the NADH-linked xylose reductase activity is in line with this hypothesis. A comparative study with various xylose-assimilating yeasts showed that significant alcoholic fermentation of xylose occurred only in those organisms which possessed NADH-linked aldose reductase.