Effects Of Different Valences Of Cerium Ion On Conformation Of Horseradish Peroxidase

Our previous studies have demonstrated that Ce⁴⁺ could induce ROS (reactive oxygen species) burst as a signal to promote pacilitaxel biosynthesis in suspension cultured Taxus cuspidate cells. To further understand the mechanism of effects of cerium ion on the ROS burst, we carefully studied the changes of the conformation of HRP treated by cerium ions, and we gained some results below:1. Ce⁴⁺ is much more efficient in reduced the value of Vmax, Km, and HRP activity than Ce³⁺. The extent of the reduced value increases accompanied by the increase of the concentration of cerium ions.2. This thesis used synchronous fluorescence spectrum, uv-visible spectrum and electron paramagnetic resonance (EPR) to detect the change of HRP tertiary structure. The change of florescence spectrum caused by Ce⁴⁺ and Ce³⁺ is opposite; although the current of uv-visible spectrum changes caused by cerium ions is similar, the changed caused by Ce⁴⁺ is still much evident than that caused by Ce³⁺; furthermore, g factor (gx and gy) in EPR induced by Ce⁴⁺ and Ce³⁺ was significantly different.3. Circular dichroism (CD) and infrared spectrum are used to compute the content of secondary structure. The percentage of transition from helical content and other structure toβstrands andβturns caused by Ce⁴⁺ is more than Ce³⁺. These results indicate that the different valence of cerium ion induces various changes of HRP conformation, and Ce⁴⁺ is more effective than Ce³⁺. This suggests that Ce⁴⁺ affects the burst of ROS through changing the conformation of redoxases.