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 lower inositol phosphates and inorganic orthophosphate. Two commercial strains of baker's yeast (Saccharomyces cerevisiae), Y-1 and Y-2, were able to express phytase activity. This was determined by the capacity to grow in a synthetic medium with IP6 as the sole phosphorus source. IP6 hydrolysis was rapid for both strains, and after 24 h, all IP6 was degraded. Control cultures 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 IP6. There was some difference in growth yield (milligrams of biomass per milligram of glucose) between the two strains: 0.95 (Y-1) and 1.35 (Y-2) in IP6 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.