Purification and characterization of a phytase (myo-inositol-hexakisphosphate phosphohydrolase) accumulated in maize (Zea mays) seedlings during germination

Abstract

Phytase (myo-inositol-hexakisphosphate phosphohydrolase, EC 3.1.3.8) has been purified from 5-7-day-old maize (Zea mays) seedlings, using a four-step purification procedure. The native protein has a molecular mass of about 76 kDa and is built up from two 38 kDa subunits. The pH and temperature optima of the purified enzyme were respectively 4.8 and 55 degrees C. The apparent Km for phytate was estimated to be 117 microM. Like other acidic phytases, the maize seedling enzyme exhibited a broad affinity for various phosphorylated substrates and especially for penta- and tri-phosphate esters of myo-inositol. The amino acid composition of the h.p.l.c.-purified protein indicated a high hydrophobicity (44% non-polar amino acids). Rabbit antibodies were produced in response to maize seedling phytase. Western-blot analyses clearly demonstrate that the increase of phytase activity observed during the first 7 days of germination corresponded to an accumulation of the protein in maize seedlings. Phytase accumulated essentially in the shoots (mesocotyl plus coleoptiles.