Stability and solubility studies of native and activated Aspergillus awamori feruloyl esterase

Feruloyl esterases can break the ester linkage between ferulic acid and the attached sugar of feruloyl polysaccharides, releasing ferulic acid and oligosaccharides from plant cell. The activity of native and activated feruloyl esterase (FAE-II) from Aspergillus awamori, which catalyzes the sugarcane bagasse hydrolysis, was studied using two analytical techniques (HPLC and UV–vis spectrophotometry). The activation of native feruloyl esterase (FAE-II), by its binding with calcium ion, resulted in an increase of Vmax of two times, and a higher sensitivity of the enzyme to product and guanidine hydrochloride denaturation, with almost no change in the Km for ferulic acid. The kinetic and thermodynamic parameters associated with the activation of FAE-II enzyme by the interaction with calcium ions were calculated and explained to show how calcium ions are involved. Also, the denaturation effect of guanidine hydrochloride (GdnHCl) towards FAE-II feruloyl esterase was studied using far UV-circular dichroism spectra. In addition, the densities and solubility of the activated FAE-II enzyme by calcium ions were determined and discussed under different conditions of temperatures and pH medium.