ARS | Publication request: Salt Effect on the pH Profile and Kinetic Parameters of Microbial Phytases

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 26, 2008
Publication Date: April 10, 2008
Citation: Ullah, A.H., Sethumadhavan, K., Mullaney, E.J. 2008. Salt effect on the pH profile and kinetic parameters of microbial phytases. Journal of Agricultural and Food Chemistry. 56:3398-3402.

Interpretive Summary: Phytase is an enzyme that is capable of degrading phytic acid in the gut environment of simple stomached animals notably poultry and swine. Phytic acid, which is abundant in cereals and legumes, is considered an anti-nutrient for they bind minerals thus depriving the animal their needed nutrients. The undigested phytic acid overloads the environment due to its abundance in the manure. Microbes present in the air feast on the manure rich in nutrients releasing phosphates, which than pollute coastal waters resulting in harmful algal bloom and toxic fish kill. Phytase in the feed could reverse the process by allowing the animal to store phosphate in their body and by producing manure with a lot less phytic acid. We have described a fungal phytase that could degrade phytic acid efficiently in the test tube. Based on our earlier results industry is now producing fungal phytase and marketing the enzyme as a feed supplement to combat phosphate pollution in the environment. While the enzyme is fast acting, the industry demands a phytase with higher activity and heat stability. To achieve this goal, we are improving the enzyme using computer simulation and genetic engineering. In this paper we showed that common salt could boost phytase's activity. A molecular mechanism is proposed in this paper; based on which we could improve the enzyme's function by genetic means.

Technical Abstract: The pH profiles of two well-characterized microbial phytases were determined. Four different general-purpose buffers at different pH were used. The roles of calcium chloride, sodium chloride, and sodium fluoride on activity were compared in these buffers. For Aspergillus niger phytase, calcium extended the pH range to 8.0. A high concentration of sodium chloride affected the activity of fungal phytase in the pH 3-4 range and shifted the pH optimum to 2.0 from 5.5 in E. coli phytase. As expected, both the microbial phytases were inhibited by sodium fluoride at acidic pHs. Since the Km for phytate increased nearly two-fold for fungal phytase while Vmax increased about 75% in high concentration of sodium chloride, it is possible that salt enhanced product to dissociate from the active site due to altered electrostatic environment.