Study Of Interaction And Structure-Activity Relation-ships Between Antioxidant And Bovine Serum Albumin

Antioxidants are added to foods to prevent or delay nutritional loss due to microbial,enzymatic,or chemical changes in foods,and to extend the shelf life and quality of foods.The absorption,distribution,metabolism and toxicity of antioxidants in organisms are closely related to the binding mechanism of food additives and proteins.Serum albumin(SA)is the most abundant protein in plasma,and is the storage and transport protein for many endogenous and exogenous compounds.If the antioxidant and SA have a strong binding effect,their metabolism and excretion in the body will be slow,the half-life will increase,and even side effects be caused.On the other hand,the interaction between antioxidants and SA will lead to changes in protein conformation,which may affect the function of the carrier protein.Therefore,the interaction between antioxidants and SA is studied to further understand the binding mechanism at the molecular level and to estimate the toxicology of antioxidants.The main research contents are:The binding mechanism of three antioxidant alkyl gallates propyl gallate(PG),octyl gallate(OG),dodecyl gallate(DG)with similar structures and BSA,the structure-activity relationship between their structure and the effect on the conformation of BSA were studied by multispectral and cyclic voltammetry.Fluorescence quenching experiment results show that the fluorescence quenching mechanism of three alkyl gallates for BSA was static quenching.At 298 K,the binding constants(K_b)of PG,OG,DG and BSA were(2.80±0.15)×10⁴L·mol^-1,(7.32±0.16)×10⁴L·mol^-1,(3.26±0.14)×10⁵L·mol^-1,respectively.Thermodynamic parameters and site marker competitive experiments proved that the three alkyl gallates and BSA formed relatively stable complex through hydrophobic interaction at site I of subdomain IIA.Synchronous fluorescence spectroscopy,Three dimensional fluorescence spectroscopy and infrared spectroscopy proved that all three alkyl gallates induced the conformational changes of BSA.The basic structure of alkyl gallate was the main reason for the fluorescence quenching and conformational changes of BSA.The binding force of DG and BSA was stronger,and it had a greater impact on the conformation of BSA.However,the difference in structure affects the structure-activity relationship between alkyl gallate and BSA,and the length of the carbon chain was the main factor affecting the structure-activity relationship.The binding mechanism of ethoxyquin(EQ)with BSA,and the regulatory effect of?-cyclodextrin on the binding of EQ and BSA were studied.The fluorescence quenching experiment results showed that the fluorescence quenching mechanism of BSA by EQ was static quenching.At 298K,the K_bwas(1.24±0.04)×10⁴L·mol^-1.?H(-116.1±7.07k J·mol^-1)<0,?S(-312.22±23.08 J·mol^-1·K^-1)<0,indicating that the binding force between EQ and BSA was hydrogen bond and van der Waals force.When EQ and?-cyclodextrin act together with BSA,EQ competes with?-cyclodextrin to bind to BSA.The competitive binding of cyclodextrin to BSA decreased the quenching constants and binding constants of EQ with BSA,but changed the mechanism and site of interaction between EQ and BSA.The presence of?-Cyclodextrin weakened the binding of EQ to BSA.