TRANSITION-STATE STRUCTURES FOR PHOSPHORYL-TRANSFER REACTIONS OF P-NITROPHENYL PHOSPHATE
TRANSITION-STATE STRUCTURES FOR PHOSPHORYL-TRANSFER REACTIONS OF P-NITROPHENYL PHOSPHATE
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DOI：
10.1021/ja00091a003
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发表时间：
1994-06-15
影响因子：
15
通讯作者：
ELSING, H
中科院分区：
文献类型：
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作者：
HENGGE, AC;EDENS, WA;ELSING, H
重原子同位素效应已被用来表征的过渡态的对硝基苯基磷酸盐的二价阴离子和一价阴离子的水解反应，为反应的二价阴离子在纯叔丁醇，和碱性磷酸酶催化的反应。测定了酚氧上的一级氧同位素效应（18 k（桥））、离去基团氮原子上的二级氮同位素效应（15 k）和磷酰基非桥氧原子上的二级氧同位素效应（18 k（非桥））。在95摄氏度下，水中二价阴离子反应的同位素效应为（15）k = 1.0028 +/- 0.0002，（18）k（桥）= 1.0189 +/- 0.0005，（18）k（非桥）= 0.9994 +/- 0.0005。在30 ℃下在叔丁醇中的二价阴离子反应给出的值为（15）k = 1.0039 +/- 0.0003，（18）k（桥）= 1.0202 +/- 0.0008，和（18）k（非桥）= 0.9997 +/- 0.0016。当校正温度时，结果非常相似，表明两个反应的后期过渡态结构相似，磷和非桥氧原子之间的键序几乎没有变化。同位素对一元阴离子水溶液反应的影响为（15）k = 1.0004 +/- 0.0002，（18）k（桥）= 1.0087 +/- 0.0003，（18）k（非桥）= 1.0184 +/- 0.0005，表明质子转移和键断裂都是限速的。碱性磷酸酶反应的同位素效应都接近统一，表明非化学步骤是酶促反应的限速。
Heavy-atom isotope effects have been used to characterize the transition states for the aqueous hydrolysis reactions of the p-nitrophenyl phosphate dianion and monoanion, for the reaction of the dianion in neat tert-butyl alcohol, and for the reaction catalyzed by alkaline phosphatase. The primary oxygen-18 isotope effect at the phenolic oxygen ((18)k(bridge)), the secondary nitrogen-15 effect ((15)k) in the nitrogen atom of the leaving group, and the secondary oxygen-18 isotope effects in the nonbridge oxygen atoms of the phosphoryl group ((18)k(nonbridge)) have been measured. The isotope effects for the dianion reaction in water at 95 degrees C were (15)k = 1.0028 +/- 0.0002, (18)k(bridge) = 1.0189 +/- 0.0005, and (18)k(nonbridge) = 0.9994 +/- 0.0005. The dianion reaction in tert-butyl alcohol at 30 degrees C gave values of (15)k = 1.0039 +/- 0.0003, (18)k(bridge) = 1.0202 +/- 0.0008, and (18)k(nonbridge) = 0.9997 +/- 0.0016. When corrected for temperature, the results are very similar, indicating similar late transition state structures for the two reactions with little or no change in bond order between the phosphorus and the nonbridge oxygen atoms. The isotope effects on the aqueous reaction of the monoanion were (15)k = 1.0004 +/- 0.0002, (18)k(bridge) = 1.0087 +/- 0.0003, and (18)k(nonbridge) = 1.0184 +/- 0.0005, suggesting both proton transfer and bond cleavage are rate-limiting. The isotope effects on the alkaline phosphatase reaction are all near unity, indicating that a nonchemical step is rate-limiting for the enzymatic reaction.