Effect Of Interaction Between Surfactant And Carbonic Anhydrase On Enzymatic Catalytic Activity

Carbonic anhydrase?CA?is a powerful bio-catalyst that accelerates the conversion of carbon dioxide to bicarbonate,which is of great significance in terms of environmental protection.One of the critical challenges is to retain the activity of CA in a long duration in its ambient condition.Previous studies have shown that the catalytic activity and stability of the enzyme can be regulated by surfactant additives.In this thesis,isothermal titration calorimetry?ITC?,ultraviolet-visible spectroscopy?UV-vis?,micro-dissolved calorimetry,etc.were used to study the interaction of carbonic anhydrase with conventional cationic surfactants,gemini cationic surfactants or zwitterionic surfactants.The activities of CA in the presence of the surfactants and their absence were assessed by the hydrolysis rate of nitrophenyl acetate and the resolution rate of CO₂ into aqueous solutions.The main research contents were as follows:1.Study of the interaction between surfactants and CA by ITCThe interactions between surfactants and CA were studied by ITC measurements.The experimental results showed that the thermodynamics of the interaction between surfactant and CA was related to the charge properties of the polar head-group.Cationic surfactant?TTAB?can attach to the opposite charge sites of the anionic amino acid residues on CA surface,following the successive processes on the specific interaction,formation of clusters on CA surface,and formation of free micelles and the attached micelles on the CA surface.The interactions should affect the activity of CA to some extent.The interaction between zwitterionic surfactant SB3-12 or CB1-14 and CA was relatively weak.2.Study on the effect of surfactants on CA activity by absorption spectroscopyThe hydrolysis of p-nitrophenyl acetate?p-PNA?catalyzed by CA in the presence of surfactant was assessed by UV-vis,which can characterize the effect of surfactant on enzyme activity.The results showed that the emzymatic activity was retained relatively about 90%before cmc of cationic,cationic gemini and zwitterionic surfactants.CA exhibited higher enzymatic activity in the presence of cationic surfactant12-s-12,DTAB,or TTAB than that in the zwitterionic surfactant SB3-12 or CB1-14.The zwitterionic surfactants CB1-14 and SB3-12 had no significant effect on the activity of enzyme CA,but they can help protect the natural structure of CA and promote the stability in the ambient condition in use.3.Effect of surfactants on enzymatic CO₂ hydration by micro-dissolution calorimetryThe effects of surfactant micelles on enzymatic CO₂ hydration were characterized by micro-dissolution calorimetry,in which the reaction rate can be assessed by the change of the observed enthalpy over the full process of CO₂ dissolution.CA can catalyze rate of CO₂ hydration reaction but can not change the solubility of CO₂.From the absorption microcalorimetry curve and observed enthalpy values in PCB,CA-PCB,surfactant?TTAB,SB3-12,CB1-14?micelles-PCB and CA-PCB solution containing surfactant micelles,it was found that surfactant micelles did not change the hydration process of CO₂.Cationic TTAB micelles had a negative effect on the enzymatic activity of CA for CO₂ hydration,while the zwitterionic SB3-12 and CB1-14 micelles had no obvious effect on the activity.