Coderoni S, Paparelli M, Gianfranceschi G L
Department of Cell Biology, University of Camerino, Italy.
Mol Biol Rep. 1990 Feb;14(1):35-9. doi: 10.1007/BF00422713.
Calf thymus DNA-Topoisomerase I activity was found to be altered by changing in phosphorylation: it was completely inhibited upon dephosphorylation by alkaline phosphatase, but incubation with N II protein kinase and ATP restored the relaxation activity to a level higher than that observed prior to dephosphorylation. The calf thymus Topoisomerase I-mediated DNA cleavage, induced by camptothecin, also proved to be inhibited by dephosphorylation, which, apparently, stabilizes the initial enzyme-substrate complex. We conclude that: the native protein is partially phosphorylated, the phosphorylation involvement is essential for the activity expression and also for DNA-protein interaction, changes in the degree of phosphorylation might be involved in the regulation of DNA processing; that evokes some properties of chromatinic peptide models, which bind DNA only when phosphorylated and leads to the assumption that they represent the minimum functional substrate for N II protein kinase.
研究发现，小牛胸腺DNA拓扑异构酶I的活性会因磷酸化状态的改变而发生变化：经碱性磷酸酶去磷酸化后，其活性被完全抑制，但与N II蛋白激酶和ATP一起温育可使松弛活性恢复到高于去磷酸化前观察到的水平。喜树碱诱导的小牛胸腺拓扑异构酶I介导的DNA切割也被证明会因去磷酸化而受到抑制，这显然稳定了初始的酶-底物复合物。我们得出以下结论：天然蛋白部分磷酸化，磷酸化参与对于活性表达以及DNA-蛋白质相互作用至关重要，磷酸化程度的变化可能参与DNA加工的调控；这引发了染色质肽模型的一些特性，即它们仅在磷酸化时结合DNA，并导致推测它们代表N II蛋白激酶的最小功能底物。
