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United States Department of Agriculture

Agricultural Research Service

Title: Differences in the Active Site Environment of Aspergillus Ficuum Phytases

Authors
item Ullah, Abul
item Sethumadhavan, Kandan

Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 30, 1997
Publication Date: N/A

Interpretive Summary: Soybean and several other meals contain an undesirable component called phytic acid. This compound, when present in the animal feed for monogastric animals, binds essential metals thus interfering with mineral and protein nutrition. The animals lack phytase, a degradative enzyme, in their digestive tract to facilitate breakdown of phytic acid. The other problem is that the animals cannot use the phosphorus contained in phytic acid. This creates an environmental problem when the animal waste is left alone in the farmland. It is imperative that phytic acid be degraded in the digestive tract of animals for two purposes, namely, to enhance mineral and phosphate utilization by the animals, and lower phosphate pollution in the groundwater. A phytase has been developed as an animal feed additive. We have also identified another phytase that shows promise for degrading phytic acid at a lower pH. We are trying to understand the major differences between these two phytases. In this paper we show that indeed these two phytases are different as far as the chemistry of the active center is concerned. This finding will enhance our knowledge of the function and structure of the second phytase. Also, we can further improve the function of the other phytase by knowledge gained from the structure of the second phytase. This knowledge will speed up the development of an optimum phytase as an animal feed additive. The animal feed industry will be the primary beneficaries of this research.

Technical Abstract: While Aspergillus ficuum phytase A (phyA) was rapidly inactivated by either 1,2-cyclohexanedione and phenylglyoxal, both specific modifiers of arginine, phytase B (phyB) showed a markedly different behavior. In the first place, phyB was totally insensitive to 1,2-cyclohexanedione even in the presence of 0.2M guanidinium hydrochloride; secondly, the enzyme showed a great deal of resistance to inactivation by phenylglyoxal. Taken together, these results indicate that the chemical environment of the active site of phyB is very different from the active site of phyA. Despite sequence similarities of the active site region in these two proteins, their differential behavior to arginine modifiers indicates that other parts of the protein play a role in the active site formation. We expected some differences in the structure since the proteins have dissimilar kinetic parameters and pH optima.

Last Modified: 11/24/2014
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