Salt Effect on the pH Profile and Kinetic Parameters of Microbial Phytases

• Published in: Journal of agricultural and food chemistry 2008-05, Vol.56 (9), p.3398-3402
• Main Authors: Ullah, Abul H. J, Sethumadhavan, Kandan, Mullaney, Edward J
• Format: Article
• Language: English
• Subjects: 6-Phytase - chemistry; 6-Phytase - metabolism; Aspergillus niger - enzymology; Binding Sites; Biological and medical sciences; Calcium Chloride - pharmacology; Escherichia coli - enzymology; Food Chemistry/Biochemistry; Food industries; Fundamental and applied biological sciences. Psychology; histidine acid phosphatase (HAP); histidine acid phytase (Haphy); Hydrogen-Ion Concentration; Kinetics; Models, Molecular; Phytase; Sodium Chloride - pharmacology; Sodium Fluoride - pharmacology; Substrate Specificity; substrate specificity site (SSS)
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf073137i

The pH profiles of two microbial phytases were determined using four different general purpose buffers at different pH values. 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 Escherichia coli phytase. As expected, both of the microbial phytases were inhibited by sodium fluoride at acidic pH values. Because the K m for phytate increased nearly 2-fold for fungal phytase while V max increased about 75% in a high concentration of sodium chloride, it is possible that salt enhanced the product to dissociate from the active site due to an altered electrostatic environment. Modeling studies indicate that while the active site octapeptide’s orientation is very similar, there are some differences in the arrangements of α-helices, β-sheets, and coils that could account for the observed catalytic and salt effect differences.