Gjerset R A, Martin D W
J Biol Chem. 1982 Aug 10;257(15):8581-3.
Nucleoplasm prepared from murine erythroleukemia cells was assayed from enzymatic activity which removes methyl groups from DNA methylated at the internal C of the sequence 5'-CCGG-3' (Hpa II sites). Under the conditions of assay, the release of methyl groups was linear with time for 1 h, and up to 2 pmol could be released per microgram of extract protein. The activity was proportional to the amount of added extract and was sensitive to heat ant to proteinase K exposure. The initial velocity was hyperbolic with increasing amounts of substrate, and the Km for methyl groups was estimated to be between 1 and 1.5 microM. These results show that DNA demethylation catalyzed by extracts from cell nuclei can occur in vitro where no DNA synthesis is occurring and suggest that such a process might occur in vivo to alter DNA methylation during differentiation.
对从小鼠红白血病细胞制备的核质进行了酶活性测定，该酶活性可从在5'-CCGG-3'序列（Hpa II位点）内部C处甲基化的DNA上去除甲基基团。在测定条件下，甲基基团的释放1小时内与时间呈线性关系，每微克提取物蛋白质最多可释放2皮摩尔。该活性与添加的提取物量成正比，并且对热和蛋白酶K处理敏感。随着底物量增加，初始速度呈双曲线，甲基基团的Km估计在1至1.5微摩尔之间。这些结果表明，细胞核提取物催化的DNA去甲基化可在无DNA合成的体外发生，这表明这样的过程可能在体内发生以在分化过程中改变DNA甲基化。
