Molecular and catalytic properties of phytate-degrading enzymes (phytases)

Phytate-degrading enzymes catalyse the step-wise release of phosphate from phytate, the principle storage form of phosphorus in plant seeds and pollen. They are widespread in nature, occurring in plants and micro-organisms, as well as in some animal tissues. Phytate-degrading enzymes have been studied intensively in recent years because of the great interest in such enzymes for reducing phytate content in animal feed and food for human consumption. Phytate-degrading enzymes are also of interest for producing defined breakdown products of phytate for kinetic and physiological studies. Certain myo-inositol phosphates have been proposed to have novel metabolic effects and therefore, the physiological role of different myo-inositol phosphates is presently undergoing extensive research. Generally, phytase behaves like a monomeric enzyme with molecular masses between 40 and 70 kDa. Up to now, two main types of phytate-degrading enzymes have been identified; acid phytate-degrading enzymes with an pH optimum around pH 5 and alkaline phytate-degrading enzymes with an pH optimum around pH 8. Most of the so far described phytate-degrading enzymes belong to the acidic type, and their optimal pH ranges from 4.5 to 6.0. This review summarises the molecular features as well as catalytic properties of phytate-degrading enzymes and also discusses enzymatic phytate degradation.