Study On Alcohol Dehydrogenase Immobilization By Modified Sol-gel Process And Adsorption

Enzyme immobilization by traditional sol-gel approach suffers from thedrawbacks of relatively high enzyme activity loss and high mass transfer resistance,solutions to this problem have been tentatively exploited herein, PEGs wereemployed as multifunctional additives to enhance immobilized enzyme activities: 1.Tetraethylorthosilicate (TEOS) derived gel is modified in the presence ofpolyethylene glycol (PEG, molecular weight 600), the effects of PEG addition to theprecursor solution on the microstructure of the gel are studied, the size of pores isincreased in the resultant gels on the bridge-linkage between PEG and precursor,thus diffusion rates is comparably increased to1.4 times. 2. PEG SuccinimidylCarbonate (SC-PEG, molecular weight 5,000) is used to modify alcoholdehydrogenase (ADH) before being immobilized in the gel in order to avoid thedamage of enzyme in sol-gel process and also improve the properties of gels such ashydrophilicity. The activities of diverse immobilized ADH have been investigated bythe enzymatic reaction of converting formaldehyde into methanol: unmodified gelimmobilized modified ADH(Immobilized ADHâ…¢)>modified gel immobilizedmodified ADH(Immobilized ADHâ…£)>modified gel immobilized unmodified ADH( Immobilized ADH â…¡ ) > unmodified gel immobilized unmodified ADH(ImmobilizedADHâ… ).And the stabilities of immobilizedADHâ…¡,ADHâ…¢,ADHâ…£ are higher than that of immobilized ADHâ… . This result indicated that enzymeactivities after the modification of gel and the modification of ADH respectivelysignificantly increased compared to the native immobilized ADH, but modificationon ADH is more effective. In addition, in order to compare the enzyme immobilization differencesbetween adsorption immobilization process and sol-gel encapsulation process. ADHis respectively immobilized onto macroporous silica carrier by adsorption and intomicroporous silica gel by sol-gel encapsulation. Through the study of adsorptionkinetics and adsorption equilibrium, the kinetics curve and adsorption isotherm areobtained. The adsorption isotherm is fitted by Langmuir equation. The effect of poresize on the adsorption capacity is examined. The sol-gel encapsulated ADH isprepared with silica matrix. The catalytic activities of the above-mentionedimmobilized ADHs towards the conversion of formaldehyde into methanol arecompared. The initial rates of enzymatic reaction catalyzed by adsorptionimmobilized ADH is higher than that catalyzed by sol-gel encapsulated ADH,whereas the Michaelis constants of the former are less than that of the latter. Theseresults indicate that the catalytic activity of adsorption immobilized ADH is higherthan that of sol-gel encapsulated ADH.