Identification and properties of myo-inositol hexakisphosphate phosphohydrolases (Phytases) from barley (Hordeum vulgare)

Two phytate-degrading enzymes (myo-inositol hexakisphosphate phosphohydrola se) have been purified from 4-day-old barley seedlings. One phytase (P2) wa s identified as a constitutive enzyme, whereas the other one (P1) was induc ed during germination. Both phytases were successfully separated from the m ajor acid phosphatases. The molecular masses of the native monomeric enzyme s 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 wa s found at 45 degrees C (P1) and 55 degrees C (P2), respectively. Kinetic p arameters for the hydrolysis of Na-phytate are K-M 72 mu M, k(cat) 136 s(-1 ()P1) and K-M 190 mu M k(cat) 43 s(-1) (P2) at 35 degrees C and optimal pH . The barley phytases exhibit a broad affinity for various phosphorylated c ompounds and hydrolyse phytate in a step-wise manner. With both phytases, t he first hydrolysis product was identified as D/L-Ins(1,2,3,4,5) P-5. (C) 2 000 Academic Press.