|Lei, X - CORNELL UNIVERSITY|
Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 2000
Publication Date: N/A
Interpretive Summary: Phytic acid is abundant in soybean and other legumes. This creates a serious problem in the use of soybean meals as a feed to poultry and hog industries. Phytic acid can bind essential minerals and proteins and thereby deprive animals from getting enough of the minerals and proteins. Therefore, from a nutritional standpoint phytic acid is an anti-nutrient. Also, undigested phytic acid in the manure causes phosphate pollution in the groundwater near large poultry and hog production facilities. The excess phytic acid in the animal manure when dumped outside for decay serves as nutrient for microbes. By the action of microbial enzyme phytase, acid is degraded rapidly and consequently phosphate is released in the environment. Rainwater washes the released phosphate and thereby contaminates groundwater. To combat these two serious problems we recommended that an active fungal enzyme call phytase be used in the feed to digest phytic acid in the gut of the animal. We are still searching fo native phytase with superior characteristics. It was reported earlier that Aspergillus fumigatus phytase with superior attributes. By cloning the gene for phytase from Aspergillus fumigatus and later by characterizing the protein we showed that the enzyme produced by this fungus falls short of the benchmark phytase produced by another species of Aspergillus. The findings of this manuscript will benefit phytase researchers worldwide to evaluate the digestive properties of Aspergillus fumigatus phytase, which is inferior to benchmark phytase produced by Aspergillus niger from the standpoints of digestive rate and its ability to withstand high temperature These two attributes are what the phytase researchers are looking up close in any new phytase before they would call the phytase a superior one.
Technical Abstract: The gene for Aspergillus fumigatus (phyA) was cloned and expressed in Pichia pastoris. The enzyme expressed was purified to near homogeneity using sequential ion-exchange chromatography and was characterized biochemically. Although, A. fumigatus phytase shows 66.2% sequence homology with A. ficuum phytase, the most widely studied enzyme, the cloned dphytase showed identical molecular weight and temperature optima profile t the benchmark phytase. The pH profile of activity and kinetic parameters, however, differed from A. ficuum phytase. The cloned enzyme contains the septa-peptide RHGARYP motif, which is also identical to the active site of A. ficuum phytase. Chemical probing of the active site Arg residues using both cyclohexanedione and phenylglyoxal resulted in the inactivation of phytase. The cloned A. fumigatus phytase, however, was more resistant to phenylglyoxal-induced inactivation. Both the thermal characterization data aand kinetic parameters of cloned and expressed A. fumigatus phytase indicate that this biocatalyst is not superior to the benchmark enzyme. The sequence difference between A. fumigatus and A. ficuum phytase may explain why the former enzyme catalyzes poorly as compared to the benchmark enzyme. In addition, differential sensitivity towards Arg modifier, phenylglyoxal, indicates a different chemical environment at the active site for each of the phytases.