Chen Allen Kuan-Liang, Breuer Michael, Hauer Bernhard, Rogers Peter L, Rosche Bettina
School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, Australia.
Biotechnol Bioeng. 2005 Oct 20;92(2):183-8. doi: 10.1002/bit.20588.
Pyruvate decarboxylase (PDC) catalyses the synthesis of asymmetric carbinols, e.g., chiral precursors for pharmaceuticals such as ephedrine and pseudoephedrine. The production of PDC by Candida utilis in a minimal medium was improved by manipulating the pH during fermentation in a 5 L bioreactor. At an aeration rate of 0.1 vvm with a stirrer speed of 300 rpm at constant pH 6, a specific PDC activity of 141 U/g dry cell weight (DCW) was achieved (average of two fermentations +/-13%). By allowing the yeast to acidify the growth medium from pH 6 to 2.9, the final specific PDC activity increased by a factor of 2.7 to 385 U/g DCW (average from 4 fermentations +/-16%). The effect of this pH drift on PDC production was confirmed by another experiment with a manual shift of pH from 6 to 3 by addition of 5 M sulfuric acid. The final PDC activity was 392 U/g DCW (average from two fermentations +/-5%). However, experiments with constant pH of 6, 5, 4, or 3 resulted in average specific activities of only 102 to 141 U/g DCW, suggesting that a transitional pH change rather than the absolute pH value was responsible for the increased specific PDC activity.
丙酮酸脱羧酶（PDC）催化不对称甲醇的合成，例如，用于生产麻黄碱和伪麻黄碱等药物的手性前体。通过在5升生物反应器中发酵过程中调节pH值，提高了产朊假丝酵母在基本培养基中PDC的产量。在恒定pH值为6、通气速率为0.1 vvm、搅拌速度为300 rpm的条件下，获得了141 U/g干细胞重量（DCW）的比PDC活性（两次发酵的平均值±13%）。通过让酵母将生长培养基的pH值从6酸化至2.9，最终比PDC活性提高了2.7倍，达到385 U/g DCW（4次发酵的平均值±16%）。通过另一个实验证实了这种pH值漂移对PDC产量的影响，该实验通过添加5 M硫酸将pH值从6手动调节至3。最终PDC活性为392 U/g DCW（两次发酵的平均值±5%）。然而，在恒定pH值为6、5、4或3的实验中，平均比活性仅为102至141 U/g DCW，这表明是pH值的过渡变化而非绝对pH值导致了比PDC活性的增加。
