Liver glycogen phosphorylase (GP) is a key enzyme for human health, as its increased activity is associated with type 2 diabetes. The GP catalytic mechanism has been explored by quantum mechanics/molecular mechanics (QM/MM) methods. Herein, we propose a mechanism that proceeds by three steps: 1) it begins with transfer of a hydrogen atom from the phosphate group of the pyridoxal 5′‐phosphate (HPO₄²⁻‐PLP) cofactor to the phosphate substrate; 2) the glycosidic linkage is then cleaved through protonation of the glycosidic oxygen atom by a hydroxy group of the inorganic phosphate group; and 3) an oxygen atom of the phosphate performs a nucleophilic attack on the anomeric carbon atom of glucose, concomitant with the return of a proton from phosphate to PO₄³⁻‐PLP, which finally leads to formation of the glucose‐1‐phosphate product and recovers the initial state of the PLP cofactor. The glycosidic bond cleavage and nucleophilic attack from the phosphate group to the glycosyl molecule have the highest activation free energies. The structural properties of the hereby characterized transition states could be very useful in structure‐based drug design studies against liver GP.

中文翻译：

---

通过对人糖原磷酸化酶的QM / MM计算了解糖原分解的限速步骤

肝糖原磷酸化酶（GP）是人类健康的关键酶，因为其活性增加与2型糖尿病有关。GP催化机理已经通过量子力学/分子力学（QM / MM）方法进行了探索。本文中，我们提出了一种机制，该机制可通过三个步骤进行：1）首先将氢原子从吡ido醛5'-磷酸（HPO ₄ ^2-- PLP）辅因子的磷酸基团转移到磷酸底物上；2）然后通过无机磷酸基团的羟基通过糖苷氧原子的质子化裂解糖苷键；3）磷酸的氧原子对葡萄糖的异头碳原子进行亲核攻击，同时质子从磷酸盐返回到PO ₄ ^3--PLP，最终导致形成葡萄糖-1-磷酸产物，并恢复PLP辅因子的初始状态。从磷酸基团到糖基分子的糖苷键裂解和亲核攻击具有最高的活化自由能。据此表征的过渡态的结构性质在针对肝GP的基于结构的药物设计研究中可能非常有用。