| Nano-technology has tremendous potential applications in biology and medicine, including disease diagnosis, drug targeting transmission, and biological sensors. Nano-silver (nanoAg) is developed into a new nano-material based on nano technology. Because of its unique characteristics, nanoAg has a wide range of applications in detection, printed electronics, disinfection and food storage. Furthermore, NanoAg materials have a close relationship with modern pharmacology and medicine. NanoAg has more qualitative bactericidal capacity and could overcome drug resistance. All mentioned above results in the relevant staff and local environmental larger dose exposure.Humans have attached great attention to its environmental hazards caused by the gradually increasing use of nanoAg. So far at home and abroad, the previous methods investigating the toxicity of nano-silver mainly focused on morphology, determination of mitochondrial function, cell proliferation, enzyme activity and cytotoxic testing. The overall level of toxicity testing has also been reported. However, there is a lack of research on the mechanism at the molecular level.In order to ensure the positive development of nano-silver materials, and reduce its injury to the natural ecological system, especially human beings, there is an urgent need to do a comprehensive and in-depth study on the toxic effects of nano-silver.This thesis includes the following three sections.In the first section the toxic effects of nanoAg on catalase were thoroughly investigated using steady state and time resolved fluorescence quench-ing measurements, ultraviolet-visible absorption spectroscopy, resonance light scattering spectroscopy (RLS), circular dichroism spectroscopy (CD) and transmission electron microscopy (TEM). NanoAg could decrease the amount of alpha-helix and increase the beta sheet stucture, leading to loose the skeleton structure of catalase. The characteristic fluorescence of catalase was obviously quenched, which showed the exposal of internal hydrophobic amino acids enhanced, and its quenching type is dynamic quenching. The result of RLS and TEM showed that the distribution and size of nanoAg become more uniform and smaller after their interaction, resulting in a decrease of RLS intensity. NanoAg could make the activity of catalase rise. By changing the structure of catalase, nanoAg increases its enzymatic activity to a certain extent, breaking down its balance in vivo, thereby affecting the normal physiological activities. NanoAg has obvious toxic effects on catalase.In the second section the effect of exposure to nanoAg on the structure of superoxide dismutase (SOD) was thoroughly investigated by fluorescence measurements, synchronous fluorescence spectroscopy, steady state and time resolved fluorescence quenching measurements, ultraviolet-visible absorption spectroscopy (UV), resonance light scattering (RLS), circular dichroism spectrum (CD), isothermal titration calorimetry (ITC) and high-resolution transmission electron microscopy (HRTEM). Through van der Waals force, nanoAg interacted with Cu-Zn SOD and influenced the active site by inducing structural changes which influence the function of SOD. The fluorescence studies show that both static and dynamic quenching processes occur.In the third section, we made a comparison of nanoAg toxicity in two diameters at the cellular level. C57BL/6J mice primary hepatocytes used for the study, we made the study of CCK-8 means exposured from nanoAg on primary mouse hepatocytes; We measured malondialdehyde (MDA), SOD activity, CAT activity at different doses of nanoAg. The experimental results showed nanoAg could induce oxidative stress and nanoAg with smaller diameter express more toxicity compared with bigger ones.The research results show that, nanoAg can affect the structure of a key enzyme as well as its function, and induce oxidative stress. It also shows a certain toxicity to molecules and cells, thereby affecting the normal physiological function of the organism. |
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