Biosynthesis, purification and some properties of extracellular phytase from Aspergillus carneus

Aspergillus carneus (Van Tiegh) Blockwitz synthesized moderate quantities of phytase in culture filtrate. Maximal enzyme yield was obtained after eight days incubation statically in a medium containing sucrose and K2HPO4 in a C/P ratio of 591.8/1 with 0.1% corn steep liquor (CSL) as the sole source of nitrogen. Substitution of (NH4)2SO4 with certain amino acids decreased phytase yields significantly. Addition of fish or soybean meal to the nitrogen-free medium failed to enhance phytase production. The enzyme was purified about 43-fold from the culture filtrate by precipitation with acetone, gel filtration through Sephadex G-75 and ion exchange chromatography on DEAE-cellulose. Activity of both crude and purified phytase was influenced greatly by changing of pH and reaction temperature: maximum activity of the crude enzyme occurred at 35 degrees C and pH 5.6, whereas that of the purified preparation at 40 degrees C and pH 5.6. The pure enzyme was found stable between pH 5.6-6.2. About 68% of the enzyme activity was lost by heating at 45 degrees C for 60 min. The pure phytase retained its activity over a long period when stored at 4 degrees C.