S-Space College of Agriculture and Life Sciences (농업생명과학대학) Dept. of Food and Animal Biotechnology (식품·동물생명공학부) Theses (Master's Degree_식품·동물생명공학부)
Effects of transhydrogenase expression on xylitol production in recombinant saccharomyces cerevisiae harboring xylose reductase gene
재조합 효모를 이용한 자일리톨 생산에서 transhydrogenase가 미치는 영향
- Issue Date
- 서울대학교 대학원
- 자일리톨; xylitol; 조효소 재순환; NADPH; soluble nucleotide transhydrogenase; Transhydrogenase; xylose reductase; Xylose reductase; S. cerevisiae; S. cerevisiae
- Thesis (master`s)--서울대학교 대학원 :농생명공학부,2003.
- Xylitol is a five-carbon sugar alcohol which is widely present in nature.
Xylitol has been used as a sugar substitute in the food industry due to a number
of functional properties.
Xylose conversion to xylitol might be controlled by the supply of NAD(P)H in
recombinant Saccharomyces cerevisiae containing the xylose reductase gene. This
thesis is concerned with effects of simultaneous expression of Azotobactor
vinelandii soluble pyridine nucleotide transhydrogenase (STH) on xylitol
production in recombinant S. cerevisiae harboring multi copies of the Pichia
stipitis xylose reductase gene (XYL1).
The STH gene which encodes an enzyme able to transfer hydrogen ion from NADH to
NADPH in a reversible manner, was expressed in the recombinant S. cerevisiae
BJ3505:¥äXR. Xylitol productivity was compared between S. cerevisiae BJ3505:¥äXR
and S. cerevisiae BJ3505:¥äXR/STH in batch and fed-batch fermentations. The
growth profiles and specific XR activity were not significantly different
between the two strains in batch culture. The specific STH activity of S.
cerevisiae BJ3505:¥äXR/STH was 2.0 unit per mg protein.
In fed-batch fermentations, xylitol production patterns were quite different.
A final xylitol concentration for S. cerevisiae BJ3505:¥äXR/STH was 59.9 g/L,
corresponding to 71% of that obtained with the S. cerevisiae BJ3505:¥äXR (84.2
g/L). Xylitol productivity of S. cerevisiae BJ3505:¥äXR/STH (1.4 g/L hr-1) was
only two-thirds than that of S. cerevisiae BJ3505:£¿R (2.1 g/L hr-1). S.
cerevisiae BJ3505:¥äXR/STH produced more by-products than the strain without the
STH gene. 4.0 g/L acetate and 16.2 g/L ethanol were produced in the S.
cerevisiae BJ3505:¥äXR/STH compared with a negligible level of acetate and 7.2
g/L ethanol for S. cerevisiae BJ3505:¥äXR. The specific XR activity was almost
the same for the two strains as observed in the batch culture. The specific STH
activity was determined approximately 3.0 unit per mg cellular protein in the S.
cerevisiae BJ3505:¥äXR/STH. The experimental results suggested that cytoplasmic
soluble pyridine nucleotide transhydrogenase directed the reaction toward the
formation of NADH and NADP+ from NAD+ and NADPH, which concomitantly reduced the
availability of NADPH for xylitol production in the recombinant S. cerevisiae
expressing the STH gene.
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