Résumé
The stepwise release of phosphate from phytate, the major storage form of phosphate in plant seeds and pollen, is initiated by a class of enzymes that have been collectively called phytases. The classification is solely due to the in vitro capability of these enzymes to accept phytate as a substrate. Phytases 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. They have a wide distribution in plants, microorganisms, and in some animal tissues. Due to several biological characteristics, such as substrate specificity, resistance to proteolysis and catalytic efficiency, bacterial phytases have considerable potential in commercial applications. In bacteria, phytase is an inducible enzyme and its expression is subjected to a complex regulation, but phytase formation is not controlled uniformly among different bacteria. It was suggested that phytase is not required for balanced growth of bacterial cells, but may be synthesised in response to a nutrient or energy limitation.