不同碳源生物转化合成L-亮氨酸的代谢计量分析

Stoichiometric Analysis of L-Leucine Biosynthesis by Using Different Carbon Sources

目的:建立黄色短杆菌利用不同碳源生物合成L-亮氨酸的代谢网络模型,并进行代谢网络计量分析。方法:通过对所构建的L-亮氨酸代谢网络模型进行途径分析,确定以果糖、葡萄糖、蔗糖或木糖为碳源时L-亮氨酸生物合成的基元模型、最大理论产率和不同模型的呼吸熵。结果:通过途径分析得到了L-亮氨酸生物合成的基元模型。以果糖、葡萄糖、蔗糖和木糖为碳源时L-亮氨酸的最大理论产率均为66.7%,其对应的最大呼吸熵分别为18、16、19、18。结论:L-亮氨酸理论得率与碳源种类无关;呼吸熵增加,能够有效提高L-亮氨酸合成代谢流,限制菌体量的过量生成。与其他碳源相比,蔗糖能够避免碳架溢流出现,合成L-亮氨酸能量代谢需求低;而葡萄糖能够较好地满足菌体生长和产酸的需求。

Objective： The stoichiometric analysis of L-leucine biosynthesis was conducted to study the effects of carbon sourses on the L-leucine production. Methods： Pathway analysis for the L-leucine production by Brevibacterium flavum was conducted when fructose, glucose, sucrose or xylose was used as substrate seperately. Results： The elementary modes, theoretical yields and respiratory quotient of L-leucine biosynthesis were finally determined. When fructose, glucose, sucrose or xylose was used as substrate, the maximal theoretical yields of L-leucine production were all 66.7% and the corresponding maximal respiratory quotients were 18, 16, 19 and 18, respectively. Conclusion： The maximal theoretical yield of L-leucine has nothing to do with carbon sources. The increase of respiratory quotient can lead to both the im- provement of L-leucine production and the decrease of biomass formation. In contrast with other carbon sources, sucrose can prevent the carbon flooding and the energy demand of L-leucine biosynthesis is lower. However glucose can contribute to both biomass formation and L-leucine production better than the others.