Effect of immobilization on pH and thermal stability of Aspergillus ficuum phytase

The phytase from Aspergillus ficuum catalyzes the hydrolysis of phytic acid into phosphoric acid and myo-inositol. The activity of this enzyme was determined by monitoring the rate of inositol production using high-performance liquid chromography methodology. The maximum activity of the enzyme was found to be approximately pH 5 and had a temperature optimum of 50 degrees C. Under this condition, the k(cat) of 96 s(-1) was obtained, and the corresponding K-m for the catalysis of phytic acid was 2.34 mM. The optimum pH for the immobilized phytase was not much different from the intact enzyme. However, the optimum temperature was increased to 58 degrees C, which is 8 degrees C higher than that of free enzyme. Apparent K-m for the immobilized enzyme was 3.28 mM, and only 34.6% of the free enzyme activity (k(cat)) was retained, (C) 1999 Elsevier Science Inc. All rights reserved.