Adsorption Of Two Metal Ions By Cry1Ac Protein And Humic Acid

Humic acid（HA）and Bacillus Thuringiensis protein have good effect on heavy metal enrichment and fixation.Bt gene crops will release Bt proteins into the soil in the form of root exudates and plant residues.This part of Bt proteins has the ability to adsorb heavy metals and will quickly adhere to the soil components,which has an impact on the distribution and activity of free metal ions in the farmland ecosystem.This study aims to explore the internal mechanism and influence of The synergistic adsorption of Cu²⁺and Pb²⁺by Cry1Ac protein and HA,to lay a theoretical and technical foundation for the development of Bt crops and the treatment of heavy metal pollution,and to expand people’s attention and understanding of this kind of research.In this study,the current commercialized Cry1Ac protein was used as the representative of Bt protein,and Cu²⁺and Pb²⁺were used as the representative of metal cation to study the binding effect of Cry1Ac protein with Cu²⁺and Pb²⁺under the influence of different factors.Using humic acid as a representative component of soil humus,the adsorption effect of HA and Cry1Ac protein on Cu²⁺and Pb²⁺.1.Cry1Ac protein binds best with metal ions at p H 8,low ionic strength and298K.The stern-Volmer equation determined that the fluorescence quenching mechanism of Cu²⁺and Pb²⁺on Cry1Ac protein was static quenching,and Cu²⁺had better protein binding ability under the same environment.The binding of Cu²⁺and Pb²⁺to Cry1Ac protein is a spontaneous endothermic process dominated by electrostatic adsorption force by Van’t Hoff equation.The addition of Cu²⁺and Pb²⁺changed the microenvironment of the Try residue of Cry1Ac protein,exposing it to more polar conditions.The Try residue moved outward from the hydrophobic interior of the protein,and the protein structure became loose.2.Ha-cry1ac protein system has better heavy metal adsorption capacity than HA monomer.High p H and low ionic strength are more favorable for the adsorption process,mainly affected by colloidal properties of HA and conformational changes of protein.In the experimental conditions,the metal ion concentration at 10 mg/L adsorption effect is the best,and with the increase of metal concentration can still maintain a high adsorption rate.The adsorption equilibrium of the two metals was reached within 180min.The quasi-second-order kinetic model is the best model to describe the adsorption kinetics of Cu²⁺and Pb²⁺on HA and Cry1Ac proteins,indicating that the adsorption process is controlled by chemical adsorption of shared electron pairs or electron transfer between the adsorbent and the adsorbed object,and the adsorption process has compound effects.Freundlich isothermal adsorption model is the best model to describe the isothermal adsorption of Cu²⁺and Pb²⁺on HA and Cry1Ac proteins,indicating that the adsorption process is multilayer adsorption distributed on the surface with heterogeneous combination and properties.The separation factor RL indicates that the increase of metal concentration is favorable to the adsorption process.3.The results of OD⁶⁰⁰ and ROS showed that HA and Cry1Ac protein did not inhibit the growth and oxidative stress of Bacillus subtilis and Escherichia coli.When the concentration of Cu²⁺and Pb²⁺is less than 20mg/L,HA and Cry1Ac proteins can reduce the influence of free heavy metal ions by adsorption and fixation.The growth of Cu²⁺and Pb²⁺was almost completely inhibited when the concentration of Cu²⁺and Pb²⁺was higher than 20mg/L,and the results of absorbance and ROS were mutually confirmed.4.The complex stability constants（log K）generated by HA synergistic Cry1Ac protein system with Cu²⁺and Pb²⁺were larger than those of HA.These results indicate that the ha-Cry1AC protein adsorbed metal ions has good stability.The adsorption of Cu²⁺and Pb²⁺on ha-Cry1ac protein is mainly due to the complexation with organic ligands,and the ion exchange effect only accounts for a part of the adsorption mechanism.The addition of Cry1Ac protein changed the surface functional groups of the complex product,resulting in n-H stretching vibration of amide A and C-N stretching of amide II group.The addition of Cry1Ac protein and the increase of HA concentration make electrostatic interaction play a greater role in its adsorption process.