A PROFICIENT ENZYME
A PROFICIENT ENZYME
复制标题
DOI：
10.1126/science.7809611
复制
发表时间：
1995-01-06
期刊：
影响因子：
56.9
通讯作者：
WOLFENDEN, R
中科院分区：
文献类型：
--
作者：
RADZICKA, A;WOLFENDEN, R
石英管中的高温反应表明，在中性水溶液中，在室温下，花生酸的脱羧率为7800万年的半衰期(t(1/2))。自发性的磷酸二酯键，如那些存在于DNA骨架中的键，在高温下进行得更慢，但活化热不那么正，因此在室温下，磷酸二甲酯在中性溶液中以13万年的t(1/2)进行水解。这些值将已知的反应的自发速率常数范围扩大到14个数量级以上，这些反应也容易受到酶的催化。相比之下，相应酶反应的二级速率常数k(Cat)/K-m的值仅限于600倍的范围。Orotidine 5‘-磷酸脱羧酶是一种非常熟练的酶，它将反应速度提高了10(17)倍，并估计在过渡状态下结合改变的底物的解离常数小于5×10(-24)M。
Orotic acid is decarboxylated with a half-time (t(1/2)) of 78 million years in neutral aqueous solution at room temperature, as indicated by reactions in quartz tubes at elevated temperatures. Spontaneous hydrolysis of phosphodiester bonds, such as those present in the backbone of DNA, proceeds even more slowly at high temperatures, but the heat of activation is less positive, so that dimethyl phosphate is hydrolyzed with a t(1/2) of 130,000 years in neutral solution at room temperature. These values extend the known range of spontaneous rate constants for reactions that are also susceptible to catalysis by enzymes to more than 14 orders of magnitude. Values of the second-order rate constant k(cat)/K-m for the corresponding enzyme reactions are confined to a range of only 600-fold, in contrast. Orotidine 5'-phosphate decarboxylase, an extremely proficient enzyme, enhances the rate of reaction by a factor of 10(17) and is estimated to bind the altered substrate in the transition state with a dissociation constant of less than 5 x 10(-24) M.