ARS | Publication request: MYO-INOSITOL HEXASULFATE IS A POTENT INHIBITOR OF ASPERGILLUS FICUUM PHYTASE

Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 8, 1998
Publication Date: N/A

Interpretive Summary: Soybeans, cotton seeds, and other lentils and beans contain phytic acid, a known antinutrient. Phytic acid is a storage form of phosphorus. It binds essential minerals thus interfering in mineral utilization in monogastric animals, i.e., poultry, pigs, humans, etc. These animals cannot digest phytic acid because they lack the enzyme phytase. One strain of fungus Aspergillus ficuum makes two different phytases, called phyA and phyB. In this paper we show that the enzyme activity could be inhibited by a compound that looks structurally similar to phytic acid. It is essential to map the active site of phytase before performing genetic engineering. Thus, the development of a specific inhibitor of phytase is crucial for improved enzyme activity. Also, with this tool we have shown that the active site of phyA is very different from phyB. Animal nutritionists working on phosphate metabolism now can use this specific inhibitor to block any phytase activity. This has implication in ruminant where the animals obtain phytase from normal flora. The development of this specific inhibitor of phytase will boost research activity among the animal nutritionists working on phytate metabolism in monogastric animals.

Technical Abstract: Myo-inositol hexasulfate (MIHS), a structural analog of the substrate myo-inositol hexaphosphate, is a potent competitive inhibitor of both phyA and phyB enzymes. The Ki of inhibition for the phyA and phyB proteins were estimated to be 4.6 mM and 0.2 mM, respectively. Thus, the phyB protein is 23-fold more sensitive to MIHS inhibition than the phyA protein. The active site geometry of phyB protein is presumed to be very different from the phyA protein as deduced by chemical probing of the enzymes by Arg-specific modifiers, i.e., 1,2-cyclohexanedione and phenylglyoxal. Probing the catalytic site of the same proteins by this newly developed specific inhibitor also gives a similar conclusion.