Division of Biochemical Technology, School of Bioresources and Technology, King Mongkut's University of Technology Thonburi, Bangkok 10150, Thailand.
Excellent Center of Enzyme Technology and Microbial Utilization, Pilot Plant Development and Training Institute, King Mongkut's University of Technology Thonburi, Bangkok 10150, Thailand.
Int J Mol Sci. 2023 Mar 29;24(7):6394. doi: 10.3390/ijms24076394.
D-Psicose is a rare, low-calorie sugar that is found in limited quantities in national products. Recently, D-psicose has gained considerable attention due to its potential applications in the food, nutraceutical, and pharmaceutical industries. In this study, a novel D-psicose 3-epimerase (a group of ketose 3-epimerase) from an extremely halophilic, anaerobic bacterium, strain SP3-1 (IfDPEase), was cloned, expressed in , and characterized. Unlike other ketose 3-epimerase members, IfDPEase shows reversible epimerization only for D-fructose and D-psicose at the C-3 position but not for D-tagatose, most likely because the Gly218 and Cys6 at the substrate-binding subsites of IfDPEase, which are involved in interactions at the O-1 and O-6 positions of D-fructose, respectively, differ from those of other 3-epimerases. Under optimum conditions (5 µM IfDPEase, 1 mM Mn, 50 °C, and pH 7.5), 36.1% of D-psicose was obtained from 10 mg/mL D-fructose. The IfDPEase is highly active against D-fructose under NaCl concentrations of up to 500 mM, possibly due to the excessive negative charges of acidic amino acid residues (aspartic and glutamic acids), which are localized on the surface of the halophilic enzyme. These negative charges may protect the enzyme from Na ions from the environment and result in the lowest pI value compared to those of other 3-epimerase members. Moreover, without adjusting any ingredients, IfDPEase could improve coconut water quality by converting D-fructose into D-psicose with a yield of 26.8%. Therefore, IfDPEase is an attractive alternative to enhancing the quality of fructose-containing foods.
D-阿洛酮糖是一种罕见的低热量糖，在天然产物中的含量有限。最近，由于其在食品、营养保健品和制药行业的潜在应用，D-阿洛酮糖引起了相当大的关注。在这项研究中，从一种极端嗜盐、厌氧细菌 中克隆、表达并表征了一种新型 D-阿洛酮糖 3-差向异构酶（一组酮糖 3-差向异构酶）， 株 SP3-1（IfDPEase）。与其他酮糖 3-差向异构酶成员不同，IfDPEase 仅在 C-3 位置对 D-果糖和 D-阿洛酮糖表现出可逆的差向异构化，而对 D-塔格糖则没有，这很可能是因为参与 D-果糖 O-1 和 O-6 位置相互作用的 IfDPEase 的底物结合亚基中的 Gly218 和 Cys6 与其他 3-差向异构酶成员不同。在最佳条件下（5 µM IfDPEase、1 mM Mn、50°C 和 pH 7.5），从 10 mg/mL D-果糖中获得了 36.1%的 D-阿洛酮糖。IfDPEase 在高达 500 mM 的 NaCl 浓度下对 D-果糖具有很高的活性，这可能是由于酸性氨基酸残基（天冬氨酸和谷氨酸）的过多负电荷位于嗜盐酶的表面。这些负电荷可能会保护酶免受环境中 Na 离子的影响，并导致其比其他 3-差向异构酶成员具有最低的等电点。此外，无需调整任何成分，IfDPEase 就可以通过将 D-果糖转化为 D-阿洛酮糖来提高椰子水的质量，转化率为 26.8%。因此，IfDPEase 是一种有吸引力的替代品，可以提高含果糖食品的质量。
