Wang Chengshan, Zheng Jiayin, Zhao Liang, Rastogi Vipin K, Shah Saumil S, DeFrank Joseph J, Leblanc Roger M
Department of Chemistry, University of Miami, Coral Gables, Florida 33146, USA.
J Phys Chem B. 2008 Apr 24;112(16):5250-6. doi: 10.1021/jp709591e. Epub 2008 Mar 29.
The secondary structure of the organophosphorus acid anhydrolase (OPAA) Langmuir monolayer in the absence and presence of diisopropylfluorophosphate (DFP) in the subphase was studied by infrared reflection-absorption spectroscopy (IRRAS) and polarization-modulated IRRAS (PM-IRRAS). The results of both the IRRAS and the PM-IRRAS indicated that the alpha-helix and the beta-sheet conformations in OPAA were parallel to the air-water interface at a surface pressure of 0 mN.m-1 in the absence of DFP in the subphase. When the surface pressure increased, the alpha-helix and the beta-sheet conformations became tilted. When DFP was added to the subphase at a concentration of 1.1 x 10(-5) M, the alpha-helix conformation of OPAA was still parallel to the air-water interface, whereas the beta-sheet conformation was perpendicular at 0 mN.m-1. The orientations of both the alpha-helix and the beta-sheet conformations did not change with the increase of surface pressure. The shape of OPAA molecules is supposed to be elliptic, and the long axis of OPAA was parallel to the air-water interface in the absence of DFP in the subphase, whereas the long axis became perpendicular in the presence of DFP. This result explains the decrease of the limiting molecular area of the OPAA Langmuir monolayer when DFP was dissolved in the subphase.
通过红外反射吸收光谱（IRRAS）和偏振调制红外反射吸收光谱（PM - IRRAS）研究了在亚相中不存在和存在二异丙基氟磷酸酯（DFP）时有机磷酸酐酶（OPAA）朗缪尔单分子层的二级结构。IRRAS和PM - IRRAS的结果均表明，在亚相中不存在DFP时，表面压力为0 mN·m⁻¹时，OPAA中的α - 螺旋和β - 折叠构象与空气 - 水界面平行。当表面压力增加时，α - 螺旋和β - 折叠构象发生倾斜。当以1.1×10⁻⁵ M的浓度向亚相中添加DFP时，OPAA的α - 螺旋构象在0 mN·m⁻¹时仍与空气 - 水界面平行，而β - 折叠构象垂直。α - 螺旋和β - 折叠构象的取向均不随表面压力的增加而改变。推测OPAA分子的形状为椭圆形，在亚相中不存在DFP时，OPAA的长轴与空气 - 水界面平行，而在存在DFP时，长轴变为垂直。该结果解释了将DFP溶解在亚相中时OPAA朗缪尔单分子层极限分子面积的减小。
