排序方式: 共有1条查询结果,搜索用时 0 毫秒
1
1.
Francisco M. Gí rio J. Carlos Roseiro Pascolina S -Machado A. Rita Duarte-Reis M. T. Amaral-Colla o 《Enzyme and microbial technology》1994,16(12):1074-1078
The titers of key enzymes of xylose metabolism were measured and correlated with the kinetics of xylitol production by Debaryomyces hansenii under different oxygen transfer rates (OTR) in a batch reactor. An OTR change from 2.72 to 4.22 mmol O2 l−1 min−1 resulted in a decrease in NADPH-dependent xylose reductase (XR) and NAD ± -dependent xylitol dehydrogenase (XDH) activities. For higher values of OTR (12.93 mmol O2 l−1 min−1, the XDH titer increased twofold whereas the XR titer did not show a significant change. At the lowest OTR (2.72 mmol O2 l−1 min−1), xylitol (and ethanol) production rates showed the highest values. However, xylitol specific productivity was twice as high as ethanol specific productivity. The titer of the NADPH-forming enzyme, glucose-6-phosphate dehydrogenase (GPDH), increased from 333 to 412 mU mg−1 when the OTR was increased. However, 6-phosphogluconate dehydrogenase (PGDH) activity remained unchanged and at a lower level, which indicates that this enzyme is responsible for the carbon flux control of the oxidative branch of the pentose phosphate pathway. The activity of the alcohol-forming enzyme was repressed at the higher amount of oxygen, decreasing its activity more than 50%. The changes in ADH suggested that two different metabolic regions under oxygen-limited conditions can be hypothesized for xylose metabolism by D. hansenii. For low OTR values (up to 4.22 mmol O2 l−1 min−1), a fermentative-type activity is displayed. At higher OTR values (above 4.22 mmol O2 l−1 min−1), no significant fermentative activity is reported. 相似文献
1