Studies On The Effect Of γ-radiation On The Conformation And Function Of Protein

In the mid-1950s, Denham Harman articulated a’free-radical theory’of ageing, speculating that endogenous oxygen radicals were generated in cells and resulted in a pattern of cumulative damage. Oxidative stress has been defined as a disturbance in the balance between the production of free radicals and antioxidant defenses. Free radicals (atoms with one or more unpaired electrons) are more generally known as reactive oxygen species (ROS) along with reactive nitrogen species (RNS). Radiation induces the radiolysis of water to generate ROS especially hydrogen radical. As a result of free radical exposure, many changes can occur in proteins, including amino acid modification, fragmentation, aggregation, formation of further reactive species. Oxidative damage to proteins may be of particular importance in vivo, since the loss of protein function may affect the activity of enzymes, receptors, and membrane transporters, among others. Most of physiological and pathological activities of Biological organism are accomplished through proteins, so related study of proteins can provide information to Law of life activities, mechanism of disease and others.Human serum albumin is the most abundant protein in blood plasma and serves as a transport and depot protein for numerous endogenous and exogenous compounds. It is a key element in the regulation of osmotic pressure, blood volume pH levels. Studies of serum albumin have also revealed the important role of this protein as a catalyst for the hydrolysis of vaious compounds, such as esters, amides, and phosphates. In this study, we use spectroscopic methods and mass spectrometry to investigate the effect of ROS generated by y-irradiation on the conformation and function of human serum albumin and bovine serum albumin. This paper has five chapters, as follows:Chapter One:We described the molecular structure and biological functions of Human serum albumin. We also introduced the physiological and pathological role of oxidative stress. ROS can lead to oxidation of amino acid residue side chains (aliphatic amino acid residues, aromatic amino acid residues, sulfur-containing amino acid residues), formation of protein-protein cross-link-ages, and oxidation of the protein backbone resulting in protein fragmentation. Radical-related damage to DNA, to proteins and to lipids has been proposed to play a key role in the development of age-dependent diseases such as cancer, arteriosclerosis, arthritis, neurodegenerative disorders and other conditions. Antioxidant defense systems include enzymatic antioxidants and non-enzymatic antioxidants. At the end of the first chapter, we introduced the relationship between radiation and human health.Chapter Two:we use spectroscopic methods to investigate the effect of ROS generated by y-irradiation on the conformation and function of HSA. The radiation effects on the secondary and tertiary structures, esterase activity and other molecular properties of HSA are determined. The results of fluorescence spectroscopy and CD spectra indicated that the oxidation by y-irradiation could disturb the secondary structures of HSA molecule. Determination of protein hydrophobicity showed that the effective hydrophobicity of HSA was decreased regularly because of oxidation by y-irradiation. Besides, small changes in the esterase-like activity of HSA were introduced. The content of bityrosine increased markedly because of oxidation of the protein, suggesting that HSA molecules were aggregated. Moreover, there were no changes in this properties of HSA in low γ-irradiation does; only higher radiation does can introduce changes in this propertie s of protein.Chapter Three and Chapter Four:we studied the effect of y-irradiation on bo vine serum albumin and human serum albumin. Different peptides presented different degree of oxidation with the increase of radiation does. The+16 Da oxidation products of BSA showed that the oxidation degree of some peptides were under 10% such as LVNELTEFAK and AEFVEVTK; some were between 10%-50% such as FGER and GACLLPK; some were exceeded 50% such as YTR and TPVSEK. The +16 Da oxidation products of BSA showed that the oxidation degree of some peptides were under 10% such as SLHTLFGDELCK and LKPDPNTLCDEFK; some were between 10%-50% such as YLYEIAR and ADEK; some were exceeded 50% such as FWGK, IETMR and CASIQK. The oxidation degree of some peptides increased, others had no obvious change, and some peptides generated new products. These differences were due to different kinds of amino acid residues that peptide contained. Moreover, their position in the protein structure can also influence the degree of oxidation.Chapter Five:We concluded the research parts above and analyzed the development direction and perspectives for study of γ-irradiation on proteins.This paper studies the effect of irradiation on organisms, which contributes to the diagnosis and treatment of diseases caused by radiation.