Purification, characterization and properties of phytase from Shigella sp. CD2.

Phytases catalyze the release of phosphate from phytic acid. In this study, a phytase producing bacterial strain Shigella sp. CD2 was isolated from the wheat rhizosphere. Phytase production started from the exponential phase of bacterial growth, showing the highest activity during the stationary phase. The enzyme activity was detected in both periplasmic and intracellular fractions. The enzyme was purified by about 133-fold with specific activity 780 U mg-1 protein. The optimum pH and temperature of the enzyme was 5.5 and 60oC, respectively. The enzyme was thermostable and retained 100% and 75% of its activity on pre-incubation at 70o and 80oC for 30 min, respectively. The Km value for the substrate sodium phytate was 0.25 mM. The enzyme was highly specific to substrate phytate, and no activity was detected in presence of other phosphorylated substrates, such as ATP, ADP, glucose 6-phosphate, fructose 6-phosphate and p-nirophenyl phosphate. The activity declined dramatically in presence of Cu2+, Zn2+ and Fe2+ and SDS, whereas Mg2+ and Co2+ slightly enhanced the enzyme activity. The addition of other metal ions or chemicals had little or no effect on phytase activity. The enzyme was resistant to both pepsin and trypsin. Due to high specific activity, substrate specificity, good pH profile, protease insensitivity and thermostability, phytase encoding gene from Shigella sp. CD2 could be an interesting candidate for industrial applications. Further studies on cloning and expression of Shigella phytase gene are currently in progress.

Purification and characterization of phytase with a wide pH adaptation from common edible mushroom Volvariella volvacea (Straw mushroom).

A novel phytase with a molecular mass of 14 kDa was isolated from fresh fruiting bodies of the common edible mushroom Volvariella volvacea (Straw mushroom). The isolation procedure involved successive chromatography on DEAE-cellulose, CM-cellulose, Affi-gel blue gel, Q-Sepharose and Superdex-75. The enzyme was a monomeric protein and was unadsorbed on DEAE-cellulose, CM-cellulose and Affi-gel blue gel, but was adsorbed on Q-Sepharose. The enzyme was purified 51.6-fold from the crude extract with 25.9% yield. Its N-terminal amino acid sequence GEDNEHDTQA exhibited low homology to the other reported phytases. The optimal pH and temperature of the purified enzyme was 5 and 45oC, respectively. The enzyme was quite stable over the pH range of 3.0 to 9.0 with less than 30% change in its activity, suggesting that it can be used in a very wide pH range. The enzyme exhibited broad substrate selectivity towards various phosphorylated compounds, but lacked antifungal activity against tested plant pathogens.

Phytase from Klebsiella Sp. No. PG-2: purification and properties.

A phytase (EC 3.1.3.8) was extracted from rat intestinal bacterium, Klebsiella Sp. No. PG.-2, and purified 50-fold by ammonium sulphate fractionation, ion-exchange chromatography and gel filtration. The enzyme is inducible in nature. The pH optimum was at 6.0 for all the inositol phosphates studied and this characterized the enzyme as an acid phosphohydrolase. Of a range of potential substrates tested, only p-nitrophenyl phosphate alongwith the inositol phosphates was hydrolyzed. It exhibits a Km of 2.0 mM; temperature optimum of 37 degrees C and energy of activation 9,120 cal/mole for all the inositol phosphates studied. The activity was inhibited by Ag2+, Hg2+, Cu2+, fluoride and high substrate concentration.