Scheiner S, Kleier D A, Lipscomb W N
Proc Natl Acad Sci U S A. 1975 Jul;72(7):2606-10. doi: 10.1073/pnas.72.7.2606.
The charge relay ststem and its role in the acylation of serine proteinases is studied using the partial retention of diatomic differential overlap (PRDDO) technique to perform approximate ab initio molecular orbital calculations on a model of the enzyme-substrate complex. The aspartate in the charge relay system is seen to act as the ultimate proton acceptor during the charging of the serine nucleophile. A projection of the potential energy surface is obtained in a subspace corresponding to this charge transfer and to the coupled motions of active site residues and the substrate. These results together with extended basis set results for cruder models suggest that a concerted transfer of protons from Ser-195 to His-57 and from His-57 to Asp-102 occurs with an energy barrier of 20-25 kcal/mole (84-105 kJ/mole). The subsequent nucleophilic attack on the scissile peptide linkage by the charged serine is then seen to proceed energetically downhill to the tetrahedral intermediate. The formation of the tetrahedral intermediate from the Michaelis complex is calculated to be nearly thermoneutral.
利用双原子微分重叠部分保留（PRDDO）技术对酶 - 底物复合物模型进行近似从头算分子轨道计算，研究了电荷中继系统及其在丝氨酸蛋白酶酰化反应中的作用。电荷中继系统中的天冬氨酸在丝氨酸亲核试剂带电过程中充当最终质子受体。在与这种电荷转移以及活性位点残基和底物的耦合运动相对应的子空间中获得了势能面投影。这些结果与更粗略模型的扩展基组结果表明，质子从Ser - 195协同转移到His - 57以及从His - 57转移到Asp - 102，能量障碍为20 - 25千卡/摩尔（84 - 105千焦/摩尔）。随后，带电荷的丝氨酸对可裂解肽键的亲核攻击在能量上向四面体中间体下坡进行。从米氏复合物形成四面体中间体的计算结果几乎是热中性的。
