Organic solvents effect on the secondary structure of araujiain hI, in different media

The aim of this work was to carry out a comparative study of the secondary structure of araujiain hI (cystein plant protease) in aqueous–organic media (N,N-dimethylformamide (50%) and hexane (50%)) and in Tris–HCl buffer (0.1 M, pH 8), using FT-IR spectroscopy. The changes in the enzyme structure were correlated with the changes in the preferences and enzyme activities in such media. The enzyme activity observed in the organic media was higher than those obtained in buffer. Although, the substrate preferences of araujiain hI exhibit different patterns in each medium, the enzyme always showed a high preference for glutamine derivative. According to the study of the secondary structure, it was possible to conclude that a secondary structure with a high α-helical character was responsible for the highest activity of araujiain hI in the studied organic media. Although, the correlation between enzyme structure and catalytic activity requires direct measurement of active-site structure and of the effect of the reaction medium on the transition state of the reaction, it is clear that the non-covalent forces which maintain the native secondary structure of enzyme were modified when araujiain hI was suspended in such aqueous–organic media.