The changes of the activity and conformation of Aspergillus niger phytase in urea were detected by farultraviolet circular dichroism （CD） spectra, fluorescence spectra, and enzyme activity assays. The results show t...The changes of the activity and conformation of Aspergillus niger phytase in urea were detected by farultraviolet circular dichroism （CD） spectra, fluorescence spectra, and enzyme activity assays. The results show that no enzyme activity can be detected after phytase is incubated for 10 h in 3.0 mol/L urea, even though at this urea concentration, less than 20% of the tertiary and secondary structures in the native enzyme changed. The inactivation reaction kinetics is found to be a monophasic first-order reaction, but the unfolding is a biphasic process consisting of two first-order reactions. The inactivation rates of the free enzyme and the substrate-enzyme complex are much faster than the conformational changes during urea denaturation. All of the results indicate that, as a glycoprotein, phytase＇s actiVity is strongly dependent on its conformational integrity. The phytase active sites seem to be located in a limited region in the molecule and display more conformational fragility and flexibility to denaturants than enzyme molecular structure as a whole.展开更多
基金Supported by the National Natural Science Foundation of China (No. 30471261)
文摘The changes of the activity and conformation of Aspergillus niger phytase in urea were detected by farultraviolet circular dichroism （CD） spectra, fluorescence spectra, and enzyme activity assays. The results show that no enzyme activity can be detected after phytase is incubated for 10 h in 3.0 mol/L urea, even though at this urea concentration, less than 20% of the tertiary and secondary structures in the native enzyme changed. The inactivation reaction kinetics is found to be a monophasic first-order reaction, but the unfolding is a biphasic process consisting of two first-order reactions. The inactivation rates of the free enzyme and the substrate-enzyme complex are much faster than the conformational changes during urea denaturation. All of the results indicate that, as a glycoprotein, phytase＇s actiVity is strongly dependent on its conformational integrity. The phytase active sites seem to be located in a limited region in the molecule and display more conformational fragility and flexibility to denaturants than enzyme molecular structure as a whole.
