Liu Wei-Qun, Rao Xue-Ming, Yu Zhen-Hang
College of Agronomy, Henan Agricultural University, Zhengzhou, Henan 450002, PR China.
Int J Biol Macromol. 2006 May 30;38(3-5):211-5. doi: 10.1016/j.ijbiomac.2006.02.017. Epub 2006 Feb 28.
The structural and functional properties of arginine kinase (AK) in alkaline conditions in the absence or presence of salt have been investigated. The conformational changes of AK during alkaline unfolding and salt-induced folding at alkaline pH were monitored using intrinsic fluorescence emission, binding of the fluorescence probe 1-anilino-8-naphthalenesulfonate and circular dichroism. The results for the alkaline unfolded enzyme showed that much lower pH (11.0) was required to cause the complete loss of AK activity than was required to cause an obvious conformational change of the enzyme. Compared with the completely unfolded state in 5M urea, the high pH denatured enzyme had some residual secondary and tertiary structure even at pH 13.0. Increasing the ionic strength by adding salt at pH 12.75 resulted in the formation of a relatively compact tertiary structure and a little new secondary structure with hydrophobic surface enhancement. These results indicate that the partially folded state formed under alkaline conditions may have similarities to the molten globule state which is compact, but it has a poorly defined tertiary structure and a native-like secondary structure.
研究了在无盐或有盐存在的碱性条件下精氨酸激酶（AK）的结构和功能特性。使用内源荧光发射、荧光探针1-苯胺基-8-萘磺酸盐的结合以及圆二色性监测了碱性pH下AK在碱性展开和盐诱导折叠过程中的构象变化。碱性展开酶的结果表明，导致AK活性完全丧失所需的pH值（11.0）远低于导致酶明显构象变化所需的pH值。与在5M尿素中完全展开的状态相比，高pH变性酶即使在pH 13.0时仍具有一些残余的二级和三级结构。在pH 12.75时添加盐增加离子强度会导致形成相对紧凑的三级结构和少量新的二级结构，同时疏水表面增强。这些结果表明，在碱性条件下形成的部分折叠状态可能与紧密的熔球态相似，但它具有定义不明确的三级结构和类似天然的二级结构。
