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Regulation of gluconate and ketogluconate production in Gluconobacter oxydans ATCC 621-H

机译:氧化葡糖杆菌ATCC 621-H中葡萄糖酸和酮葡萄糖酸的生产调节

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摘要

Gluconobacter spp. possess the enzymic potential for two pathways of direct glucose oxidation. It has been proposed that the major part of glucose is oxidized to gluconate via NADP-dependent glucose dehydrogenase and that reoxidation of NADPH under these conditions proceeds via recycling of gluconate through ketogluconates. This hypothesis was tested in experiments in which Gluconobacter oxydans ATCC 621-H was grown in glucose-yeast extract medium containing [14C]2-ketogluconate. As expected, glucose was almost quantitatively oxidized to gluconate, without further accumulation of 2- and 5-ketogluconate. Interestingly, the total amount of neither [14C]2-ketogluconate nor [14C]gluconate did change significantly during this oxidation phase, indicating that recycling of gluconate through ketogluconates did not occur. An analysis of enzyme activities in cell-free extracts of glucose-grown cells of G. oxydans ATCC 621-H showed that the membrane-bound glucose dehydrogenase was far more active than the NADP-linked glucose dehydrogenase. The activity of the latter enzyme constituted only 10-15% of that of quinoprotein glucose dehydrogenase and was far too low to match the in vivo rates of gluconate production in batch cultures of G. oxydans. It is concluded that under these conditions glucose is mainly oxidized to gluconate via the membrane-bound glucose dehydrogenase. Implications of these results for the regulation of ketogluconate formation are discussed.
机译:葡糖杆菌属。具有两个直接葡萄糖氧化途径的酶促潜力。已经提出,葡萄糖的主要部分通过依赖NADP的葡萄糖脱氢酶被氧化为葡萄糖酸盐,并且在这些条件下NADPH的再氧化通过葡萄糖酸通过酮葡萄糖酸盐的再循环而进行。该假设在实验中得到了验证,在该实验中,氧化葡糖杆菌ATCC 621-H在含有[14C] 2-酮葡萄糖酸酯的葡萄糖酵母提取培养基中生长。如所期望的,葡萄糖几乎被定量地氧化为葡萄糖酸酯,而没有2-和5-酮葡萄糖酸酯的进一步积累。有趣的是,[14C] 2-酮葡萄糖酸酯和[14C]葡萄糖酸酯的总量在此氧化阶段均未发生显着变化,表明未发生通过酮葡萄糖酸酯的葡萄糖循环。氧化酶G.oxydans ATCC 621-H的无细胞提取物中的酶活性分析表明,膜结合的葡萄糖脱氢酶比NADP连接的葡萄糖脱氢酶更具活性。后一种酶的活性仅占喹蛋白葡萄糖脱氢酶活性的10-15%,并且太低而不能与氧化单歧杆菌的分批培养物中的葡萄糖酸盐产生的体内速率相匹配。结论是在这些条件下,葡萄糖主要通过膜结合的葡萄糖脱氢酶被氧化成葡萄糖酸盐。讨论了这些结果对酮基葡萄糖酸酯形成的调节的意义。

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