Purification and properties of a low-molecular-weight phytase from Cladosporium sp. FP-1

A fungus producing high levels of phytase was isolated from air and identified as Cladosporium sp. The phytase production was stimulated by phytate in the medium used. The maximum production of phytase (108 U/ml) occurred in a medium containing 1.0 g of phytate per 100 ml. The phytase was purified to electrophoretic homogeneity by ion-exchange chromatography and gel filtration. Based on SDS-PAGE analysis, the molecular weight of the purified phytase was calculated to be approximately 32.6 kDa, and the narrow protein band indicated that this phytase is not glycosylated. The phytase has an optimum pH of 3.5, and an optimum temperature of 40 degrees C. The phytase activity was stimulated by 2-mercaptoethanol and dithiothreitol, and inhibited by Ba2+, Pb2+, iodoacetate, p-chloromercuribenzoate and phenylmethylsulfonyl fluoride. The phytase displayed high affinity for phytate and the Km was 15.2+/-3.1 microM. NMR analyses (1D and 2D) indicated that the end hydrolysis product of phytate was myo-inositol 1,2,5-triphosphate.