Influence of Water Activity on Protease Adsorbed on Biochar in Organic Solvents

摘要

We have found that the organic solvent-resistance of α-chymotrypsin (α-CT) is enhanced by adsorbing α-CT onto bamboo charcoal powder (BCP), which is obtained by pyrolyzing bamboo waste under nitrogen atmosphere, and is markedly dependent on the thermodynamic water activity (a_w) in organic solvents. When BCP-adsorbed a-CT was immersed in acetonitrile at an appropriate water activity, it effectively enhanced the transesterification of N-acetyl-L-tyrosine ethyl ester (N-Ac-Tyr-OEt) with n-butanol (BuOH) to produce N-acetyl-L-tyrosine butyl ester (N-Ac-Tyr-OBu), compared to the hydrolysis of N-Ac-Tyr-OEt with water to give N-acetyl-L-tyrosine (N-Ac-Tyr-OH). When the water activity was 0.28, the initial rate of transesterification catalyzed by BCP-adsorbed α-CT was about sixty times greater than that catalyzed by free α-CT. Regarding the reaction selectivity which is defined as a ratio of the initial rate of transesterification to that of hydrolysis, BCP-adsorbed α-CT was much superior to free α-CT. The catalytic activity of BCP-adsorbed α-CT was markedly dependent on the reaction temperature. Furthermore, concerning the thermal stability at 50 ℃, the half-life of BCP-adsorbed α-CT exhibited 3.8-fold, compared to that of free α-CT.