塔格糖-4-异构酶的新酶挖掘及酶学性质研究

d-塔格糖是一种己酮糖，在自然界中天然存在但含量极少，具有降血糖、抗龋齿、改善肠道菌群、促进血液循环和抗衰等作用，可广泛应用于食品、医药和化妆品行业。目前酶催化半乳糖生成塔格糖仅需一步反应，简单易行，但半乳糖较高的成本限制了这一方法的工业应用。果糖是塔格糖的同分异构体，价格低廉，来源稳定，可通过4位差向异构化一步获得塔格糖，是产塔格糖的理想底物。【目的】因此挖掘新的塔格糖-4-差向异构酶对塔格糖的工业生产具有重要意义。【方法】本文通过基因挖掘的手段发现了热袍菌(Thermotogae bacterium)来源的未知功能蛋白(命名为HCZ0)具有塔格糖-4-差向异构酶活性，进而完成了HCZ0的异源表达、纯化及酶学性质表征。【结果】确定HCZ0表观分子量约为57.9 kDa，比活力为0.9 U/mg，最适反应温度和pH值分别为70 ℃和9.0，最适金属离子为Ni²⁺，最适金属离子浓度为2 mmol/L，60、70和80 ℃半衰期分别为180、67和9 h。最适条件下，HCZ0催化200 g/L果糖在2 h内可产生28 g/L塔格糖。【结论】本研究中，HCZ0是碱性高温酶，且具有较好的热稳定性，这些特征在以后的理论研究及工业生产中具有一定的科学价值。     

Isolation of a nucleotide activated disaccharide pentapeptide precursor from Methanobacterium thermoautotrophicum

The yeasts Pachysolen tannophilus and Pichia stipitis differed in their ability to utilize D-xylose in the presence of D-fructose. When P. tannophilus was grown aerobically in fructose-xylose mixture, the ketohexose was utilized preferentially over the pentose. However, in P. stipitis cultures, the converse was observed. The effect was associated with the ability of D-fructose to repress the induction of xylose reductase and xylitol dehydrogenase activities in P. tannophilus but not in P. stipitis. Both yeasts grew on D-fructose and fermented it to ethanol when it was supplied as the sole carbon source. The results suggest that there may exist some fundamental difference in the regulation of D-fructose metabolism between P. tannophilus and P. stipitis.