Lee Jung-Kul, Koo Bong-Seong, Kim Sang-Yong
BioNgene Co., Ltd., Chongro-Ku, Seoul, Korea 110-521.
Appl Environ Microbiol. 2002 Sep;68(9):4534-8. doi: 10.1128/AEM.68.9.4534-4538.2002.
Torula corallina, a strain presently being used for the industrial production of erythritol, has the highest erythritol yield ever reported for an erythritol-producing microorganism. The increased production of erythritol by Torula corallina with trace elements such as Cu(2+) has been thoroughly reported, but the mechanism by which Cu(2+) increases the production of erythritol has not been studied. This study demonstrated that supplemental Cu(2+) enhanced the production of erythritol, while it significantly decreased the production of a major by-product that accumulates during erythritol fermentation, which was identified as fumarate by instrumental analyses. Erythrose reductase, a key enzyme that converts erythrose to erythritol in T. corallina, was purified to homogeneity by chromatographic methods, including ion-exchange and affinity chromatography. In vitro, purified erythrose reductase was significantly inhibited noncompetitively by increasing the fumarate concentration. In contrast, the enzyme activity remained almost constant regardless of Cu(2+) concentration. This suggests that supplemental Cu(2+) reduced the production of fumarate, a strong inhibitor of erythrose reductase, which led to less inhibition of erythrose reductase and a high yield of erythritol. This is the first report that suggests catabolite repression by a tricarboxylic acid cycle intermediate in T. corallina.
珊瑚状球拟酵母，一种目前用于赤藓糖醇工业化生产的菌株，其赤藓糖醇产量是以往报道的产赤藓糖醇微生物中最高的。关于珊瑚状球拟酵母通过添加铜离子（Cu(2+)）等微量元素来提高赤藓糖醇产量的研究已有详尽报道，但Cu(2+)提高赤藓糖醇产量的机制尚未得到研究。本研究表明，添加Cu(2+)可提高赤藓糖醇产量，同时显著降低赤藓糖醇发酵过程中积累的一种主要副产物的产量，通过仪器分析确定该副产物为富马酸。赤藓糖还原酶是珊瑚状球拟酵母中一种将赤藓糖转化为赤藓糖醇的关键酶，通过离子交换和亲和色谱等色谱方法将其纯化至同质。在体外，随着富马酸浓度增加，纯化的赤藓糖还原酶受到显著的非竞争性抑制。相比之下，无论Cu(2+)浓度如何，酶活性几乎保持不变。这表明添加Cu(2+)减少了富马酸（赤藓糖还原酶的强效抑制剂）的产生，从而减少了对赤藓糖还原酶的抑制，提高了赤藓糖醇产量。这是首次表明珊瑚状球拟酵母中三羧酸循环中间产物存在分解代谢物阻遏的报道。
