Identification and Properties of myo -Inositol Hexakisphosphate Phosphohydrolases (Phytases) from Barley (Hordeum vulgare)

Two phytate-degrading enzymes (myo -inositol hexakisphosphate phosphohydrolase) have been purified from 4-day-old barley seedlings. One phytase (P2) was identified as a constitutive enzyme, whereas the other one (P1) was induced during germination. Both phytases were successfully separated from the major acid phosphatases. The molecular masses of the native monomeric enzymes were estimated to be about 67 kDa. Both phytate-degrading enzymes belong to the acidic phytases. They exhibit a single pH-optimum at 5·0 (P1) and 6·0 (P2), respectively. Optimal temperature for the degradation of phytate was found at 45 °C (P1) and 55 °C (P2), respectively. Kinetic parameters for the hydrolysis of Na-phytate are KM72 μm, kcat136 s−1(P1) and KM190 μm, kcat43 s−1(P2) at 35 °C and optimal pH. The barley phytases exhibit a broad affinity for various phosphorylated compounds and hydrolyse phytate in a step-wise manner. With both phytases, the first hydrolysis product was identified as D/L-Ins(1,2,3,4,5) P5