α-L-ARABINOFURANOSIDASE FROM AN EFFICIENT HEMICELLULOLYTIC FUNGUS Penicillium janthinellum CAPABLE OF HYDROLYZING WHEAT AND RYE ARABINOXYLAN TO ARABINOSE

This study reports Penicillium janthinellum strain, producing high levels of alpha-L-arabinofuranosidase (AFase) as well as other components of hemicelluloytic enzyme system (endoxylanase, beta-xylosidase and acetyl xylan esterase) on rice straw and wheat bran containing solidified culture medium. Optimization of culture conditions was carried out using Box-Behnken design of experiment to study the influence of process variables (ammonium sulphate, pH and moisture level) on AFase production. Analysis of data showed R-2 (0.9967) and adjusted R-2 (0.9925) indicating model to be good fit and robust to predict culture conditions for AFase production. Under optimal culture conditions P. janthinellum produced high levels of AFase (212 units/g dw substrate) in addition to xylanase (1800 units/g dw substrate), beta-xylosidase (31 units/g dw substrate), acetyl xylan esterase (231 units/g dw substrate) and feruloyl esterase (27 units/g dw substrate). AFase from P. janthinellum culture extract was purified to homogeneity and characterized to be a 64 kDa protein with a pI of 3.8. The peptide mass fingerprinting showed the AFase belonged to family GH54. The enzyme was optimally active at 50 degrees C at pH 5.5 and its activity was positively modulated in presence of Fe(3+)ions. The enzyme preferentially catalyzed the hydrolysis of pNP-arabinofuranoside (pNPA) with Km and Vmax of 0.4mM and 260 unit mg(-1) protein(-1), respectively. Hydrolysis with purified AFase (3.0 units/g substrate) released arabinose from rye arabinoxylans (29.5 mg/g substrate) and wheat arabinoxylan (13.4 mg/g substrate), as the sole product indicating P. janthinellum as the important source of alpha-L-arabinofuranosidase for bioconversion of agro-residue to value added products.