McConaughy B L, Young L S, Champoux J J
Biochim Biophys Acta. 1981 Aug 27;655(1):1-8. doi: 10.1016/0005-2787(81)90059-9.
The optimum monovalent cation concentration (Na+ or K+) for the relaxation of superhelical DNA by the rat liver nicking-closing enzyme under conditions of DNA excess was found to be 150-200 mM. The detection of a nicked DNA species after stopping a reaction with alkali depends on having a high molar ratio of enzyme to DNA and is maximal between 50 and 100 mM monovalent cation. Varying the salt concentration from 15 to 200 mM appears to have no effect on the catalysis of the nicking -closing reaction by the enzyme. Instead different salt optima in these two assays can be explained by the observation that the nicking-closing enzyme acts by a processive mechanism below 100 mM salt and becomes nonprocessive above 150 mM. The salt elution of the nicking-closing enzyme from resting cell chromatin appears to be similar to that which one would expect for the elution of the enzyme from naked DNA. However, greater than 70% of the chromatin associated enzyme activity remained bound to chromatin from growing cells at 300 mM salt, a concentration at which there is no significant binding to naked DNA in vitro.
在DNA过量的条件下，发现大鼠肝脏切口封闭酶使超螺旋DNA松弛的最佳单价阳离子浓度（Na⁺或K⁺）为150 - 200 mM。用碱终止反应后对切口DNA种类的检测取决于酶与DNA的高摩尔比，并且在单价阳离子浓度为50至100 mM时达到最大值。将盐浓度从15 mM变化到200 mM似乎对该酶催化的切口封闭反应没有影响。相反，这两种测定中不同的盐最佳浓度可以通过以下观察结果来解释：切口封闭酶在盐浓度低于100 mM时通过持续作用机制起作用，而在高于150 mM时变为非持续作用。从静止细胞染色质中洗脱切口封闭酶的盐浓度似乎与从裸露DNA中洗脱该酶时预期的情况相似。然而，在300 mM盐浓度下，超过70%的与染色质相关的酶活性仍与生长细胞的染色质结合，在该浓度下，体外与裸露DNA没有明显的结合。
