Monday, 13 November 2006
92-5

Characterization of Phosphohydrolases Using Organophosphates.

Irenus Tazisong1, Zachary Senwo1, Robert Taylor1, and Zhongqi He2. (1) Alabama A&M University, "4900 Meridian Street, Box 1208", Normal, AL 35762-1208, United States of America, (2) USDA-ARS-New England Plt, Soil, Wtr., University of Maine, University of Maine, Orono, ME 04469, United States of America

The ease to mineralize organophosphates to release inorganic phosphorus (Pi) for plant uptake largely depends on the stereochemical structure of the compound, the types and sources of enzymes involved in addition to certain environmental factors. We determined the kinetics parameters (Vmax, Km, Kcat, and Kcat/Km) of phosphomonoesterase and phytase from various sources on seven substrates analog  [p-Nitrophenyl phosphate, Bis-P-Nitrophenyl phosphate, P-Nitrophenyl phosphate bis(cyclohexylammonium), P-Nitrophenyl phosphate di(2-amino-2-ethyl-1-3-propanediol), D-Glucose 6-phosphate sodium salt, D-Glucose 6-phosphate disodium salt, and inositol hexakisphosphate] to assess the hydrolytic respond under standard conditions. Results from this study revealed that the Vmax, Km (the binding affinity), Kcat (turnover number) and Kcat/Km (catalytic efficiency) values were different for similar enzyme from different sources. Similar trend was observed for Ea and Q10. This study suggests that the optimal condition for enzyme activity is highly dependable on the substrates. The study enhances our understanding of the biogeochemical cycling of organophosphates in the environment.

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