State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China.
School of Life Science and Food Engineering, Huaiyin Institute of Technology, Jiangsu, China.
Biochim Biophys Acta Gen Subj. 2021 Jan;1865(1):129740. doi: 10.1016/j.bbagen.2020.129740. Epub 2020 Sep 19.
In acetic acid bacteria such as Gluconobacter oxydans or Gluconobacter cerinus, pyrroloquinoline quinone (PQQ) in the periplasm serves as the redox cofactor for several membrane-bound dehydrogenases that oxidize polyhydric alcohols to rare sugars, which can be used as a healthy alternative for traditional sugars and sweeteners. These oxidation reactions obey the generally accepted Bertrand Hudson's rule, in which only the polyhydric alcohols that possess cis d-erythro hydroxyl groups can be oxidized to 2-ketoses using PQQ as a cofactor, while the polyhydric alcohols excluding cis d-erythro hydroxyl groups ruled out oxidation by PQQ-dependent membrane-bound dehydrogenases.
Membrane fractions of G. oxydans were prepared and used as a cell-free catalyst to oxidize galactitol, with or without PQQ as a cofactor.
In this study, we reported an interesting oxidation reaction that the polyhydric alcohols galactitol (dulcitol), which do not possess cis d-erythro hydroxyl groups, can be oxidized by PQQ-dependent membrane-bound dehydrogenase(s) of acetic acid bacteria at the C-3 and C-5 hydroxyl groups to produce rare sugars l-xylo-3-hexulose and d-tagatose.
This reaction may represent an exception to Bertrand Hudson's rule.
Bertrand Hudson's rule is a well-known theory in polyhydric alcohols oxidation by PQQ-dependent membrane-bound dehydrogenase in acetic acid bacteria. In this study, galactitol oxidation by a PQQ-dependent membrane-bound dehydrogenase represents an exception to the Bertrand Hudson's rule. Further identification of the associated enzymes and deciphering the explicit enzymatic mechanism will prove this theory.
在醋酸菌（如氧化葡萄糖酸杆菌或葡萄糖酸杆菌）中，周质中的吡咯喹啉醌（PQQ）作为几种膜结合脱氢酶的氧化还原辅助因子，可将多元醇氧化为稀有糖，这些稀有糖可作为传统糖和甜味剂的健康替代品。这些氧化反应遵循公认的 Bertrand Hudson 规则，即只有具有顺式 d-赤型羟基的多元醇才能被 PQQ 作为辅助因子氧化为 2-酮糖，而不具有顺式 d-赤型羟基的多元醇则被 PQQ 依赖性膜结合脱氢酶排除在氧化之外。
制备氧化葡萄糖酸杆菌的膜部分，并用作无细胞催化剂，以氧化半乳糖醇，有无 PQQ 作为辅助因子。
在这项研究中，我们报告了一个有趣的氧化反应，即不具有顺式 d-赤型羟基的多元醇半乳糖醇（山梨醇）可以被醋酸菌的 PQQ 依赖性膜结合脱氢酶在 C-3 和 C-5 羟基氧化，生成稀有糖 l-木酮-3-己酮糖和 d-塔格糖。
该反应可能代表 Bertrand Hudson 规则的例外。
Bertrand Hudson 规则是 PQQ 依赖性膜结合脱氢酶氧化多元醇的一个著名理论。在这项研究中，半乳糖醇被 PQQ 依赖性膜结合脱氢酶氧化代表了 Bertrand Hudson 规则的例外。进一步鉴定相关酶并阐明明确的酶促机制将证明这一理论。
