CIS-TRANS IMIDE ISOMERIZATION OF THE PROLINE DIPEPTIDE
CIS-TRANS IMIDE ISOMERIZATION OF THE PROLINE DIPEPTIDE
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DOI：
10.1021/ja00105a036
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发表时间：
1994-12-28
影响因子：
15
通讯作者：
KARPLUS, M
中科院分区：
文献类型：
--
作者：
FISCHER, S;DUNBRACK, RL;KARPLUS, M
分析了脯氨酸二肽的顺反酰亚胺异构化反应。结果表明，反应路径是复杂的，涉及酰亚胺键扭转角ω，酰亚胺氮，和脯氨酸主链扭转角psi的的异构化。一个虚拟的二面角ζ被发现是更好地适合于描述的反应比欧米茄的进展。在6- 31 G *//3- 21 G从头算水平上，用经验CHARMM势计算了这些坐标的绝热能量图.顺时针（syn）和逆时针（anti）路径的反式-->顺式异构化从最佳基态到过渡态的气相6- 31 G * 活化能垒分别为17.9和20.7 kcal/mol。一个强烈的依赖性的活化势垒上psi被发现，其值可以改变障碍多达12千卡/摩尔。对于类似于0度的psi，C-端NH基团可以与酰亚胺氮（顺式）或酰亚胺羰基氧（反式）的孤对电子相互作用;这两种相互作用导致势垒降低。这种过渡态的“自催化"稳定性对旋转异构酶的催化机制有一定的意义。
The cis-trans imide isomerization reaction of the proline dipeptide is analyzed. It is shown that the reaction path is complex and involves the imide bond torsion angle omega, the pyramidalization of the imide nitrogen, and the proline backbone torsion angle psi. A virtual dihedral angle zeta is found to be better suited for describing the progress of the reaction than omega. Adiabatic energy maps are calculated as a function of these coordinates with the empirical CHARMM potential and at the 6-31G*//3-21G ab initio level. The gas phase 6-31G* activation barriers for trans --> cis isomerization from the optimized ground state to the transition state are 17.9 and 20.7 kcal/mol for the clockwise (syn) and anticlockwise (anti) path, respectively. A strong dependence of the activation barrier on psi is found; its value can change the barrier by as much as 12 kcal/mol. For psi similar to 0 degrees, the C-terninal NH group can interact with either the lone pair of the imide nitrogen (syn) or the imide carbonyl oxygen (anti); both interactions result in a lowering of the barrier. This ''autocatalytic'' stabilization of the transition state has implications for the mechanism of catalysis in rotamases.