SUBSTRATE SELECTIVITY IN ASPERGILLUS-FICUUM PHYTASE AND ACID-PHOSPHATASES USING MYOINOSITOL PHOSPHATES

The three extracellular acid phosphatases produced by Aspergillus ficuum have varying affinities for myo-inositol hexakis-, pentakis-, tetrakis-, and trisphosphate. Phytase (EC 3.1.8) has previously been shown to degrade phytate at pH 5.5 and 2.5, but similar activity has not been demonstrated in the concurrently produced extracellular acid phosphatases. Data obtained in this study demonstrate that the acid phosphatase with an optimum at pH 2.5 is a potent phytase at this pH. However, the pH 6.0 optimum acid phosphatase hydrolyzes phosphate from the myo-inositol backbone very poorly. The kinetic parameters obtained for these enzymes indicate the potential value of both phytase and pH 2.5 acid phosphatase as feed additives for monogastric animals.