Urea treated subtilisin as a biocatalyst for transformations in organic solvents.

Subtilisin lyophilized from its solution in aqueous buffer in the presence of 6 M urea showed up to 50-fold increase (as compared to lyophilized subtilisin not subjected to urea treatment) in its initial rate of a transesterification reaction in anhydrous n -hexane. The lyophilization time controlling the extent of ‘drying’ was an important parameter. The urea treated subtilisin had five times shorter half life during heating at 100 °C in hexane. The change in conformation was also reflected in its 92-fold higher activity at 15 °C as compared to merely 28-fold higher activity at 45 °C. The comparative enantioselectivity of urea treated subtilisin during kinetic resolution of 1-phenylethanol was expectedly lower. Its enantioselectivity during kinetic resolution of a natural substrate N -acetyl-( R , S )-phenylalanine ethyl ester in hexane was higher. Urea treated subtilisin also showed higher catalytic promiscuity during an aldol condensation. CD studies in both far UV and near UV region were also carried out to compare the two structures. [ABSTRACT FROM AUTHOR]