Inositol hexaphosphate hydrolysis by baker's yeast. Capacity, kinetics, and degradation products

Phytases hydrolyze myo-inositol 1,2,3,4,5,6-hexaphosphate (IP6), yielding l ower inositol phosphates and inorganic orthophosphate. Two commercial strai ns of baker's yeast (Saccharomyces cerevisiae), Y-1 and Y-2, were able to e xpress phytase activity. This was determined by the capacity to grow in a s ynthetic medium with IP6 as the sole phosphorus source. IP6 hydrolysis was rapid for both strains, and after 24 h, all IP6 was degraded. Control cultu res contained inorganic orthophosphate (P-i) and no IP6. Growth rate in IP6 medium was for both strains essentially identical to growth in P-i medium, indicating a well-adapted metabolism for utilization of phosphorus from IP 6. There was some difference in growth yield (milligrams of biomass per mil ligram of glucose) between the two strains: 0.95 (Y-1) and 1.35 (Y-2) in IP 6 medium and 1.03 and 1.35, respectively, in P-i medium. The phytases were of the 3-phytase type, forming mainly DL-Ins(1,2,4,5,6)P-5, DL-Ins(1,2,5,6) P-4, and DL-Ins(1,2,6)P-3.