THE PHYTASE SUBFAMILY OF HISTIDINE ACID-PHOSPHATASES - ISOLATION OF GENES FOR 2 NOVEL PHYTASES FROM THE FUNGI ASPERGILLUS-TERREUS AND MYCELIOPHTHORA-THERMOPHILA

Phytases catalyse the hydrolysis of phytate (myo-inositol hexakisphosp hate) to myo-inositol and inorganic phosphate. In this study genes enc oding novel phytases from two different filamentous fungi, Aspergillus terreus strain 9A-1 and Myceliophthora thermophila were isolated. The encoded PhyA phytase proteins show 60% (A. terreus) and 48% (M. therm ophila) identity, respectively, to the PhyA of Aspergillus niger and h ave 21-29% identity compared to other histidine acid phosphatases. All three PhyA proteins, in contrast to the A. niger pH 2 . 5-optimum aci d phosphatase, prefer phytic acid as substrate and show enzyme activit y at a broad range of acidic pH values. Based on their enzyme characte ristics and protein sequence homology, the phytases form a novel subcl ass of the histidine acid phosphatase family.