The effect of hexane with different water content on the secondary structure of araujiain hI

GERARDO CAMÍ.; EVELINA QUIROGA.; SONIA BARBERIS.

Buenos Aires

Workshop; International Workshop on Infrared Spectroscopy Applied to Biological and Biomimetic Systems: From the Isolated Molecule to the Cell.; 2007

Buenos Aires

ST10.---------------------------------------------------------------------------FTIR spectroscopy has been used to study the secondary structure of numerous proteins in solution and in solid state (1-4). In this work, the secondary structure of araujiain hI (a plant cystein protease) in hexane with different water content and in Tris-HCl buffer (0.1 M, pH 8) was comparatively studied using FTIR spectroscopy. Changes in the araujiain hI structure were correlated with changes in the enzymatic activity in such media. The enzyme caseinolytic activity observed in hexane (50%) and in hexane (98%) was 14 and 2 times, respectively, higher than that obtained in buffer; whereas, no activity was observed in hexane (without water addition). According to the analyzed spectra (Fig. 1), the observed enzyme-solvent hydrophobic interaction with hexane altered the araujiain hI structure through a change in folding. Thus, the ratio between the -sheet and -helix areas was calculated. These results allowed concluding that a secondary structure containing high -helical character was responsible for the highest activity of araujiain hI in hexane (50%) (5). Although correlation between enzyme structure and catalytic activity requires direct measurement of the active-site structure and of the reaction medium effect on the reaction transition state, it is clear that the non-covalent forces maintaining the native secondary structure of the enzyme were modified when araujiain hI was suspended in such organic media.