Kinetic parameters of phosphatases in soils and organic waste materials

Phosphatases catalyze reactions important in P cycling in soils and for plant nutrition. We carried out this study to compare the type, pH optima, kinetic parameters (Km and Vmax), and activation energies (Ea) of phosphatases in soils and organic waste materials. Results showed that plant materials (oat, alfalfa, corn, and soybean leaves) and sewage sludges do not contain alkaline phosphatase and phosphodiesterase, respectively, and evidently they are not sources of these enzymes in soils. The optimum pH value of acid and alkaline phosphatases in soils was 1.5 units higher than those of these enzymes in the organic waste materials. The optimum pH value of phosphodies; terase in soils and animal manures was at pH = 8, but that of the same enzyme in plant materials was at pH = 5.5. The optimum pH of pyrophosphatase was 2.5 units higher than that of the activity of this enzyme in animal manures and plant materials.The average Km values of acid and alkaline phosphatases in soils and in plant materials, animal manures, and sewage sludges were similar. The average Km value of pyrophosphatase in soils (37.8 m M), however, was much higher than the Km values of this enzyme in plant materials (10.1 m M) and in animal manures (6.3 m M). Comparison of the relative concentration of the phosphatases in soils and various organic waste materials showed that, expressed on 1 g of oven-dried materials, the average Vmax values of the various phosphatases were much greater in plant materials than those in soils, animal manures, and sewage sludges. The Vmax values, however, varied considerably among the materials studied, indicating the degree of enrichment of the various materials with the phosphatases studied.Expressed in kilojoules/mole, the average Ea of acid phosphatase in four soils (42.3) was higher than those of alkaline phosphatase (32.3), phosphodiesterase (37.0), and pyrophosphatase (37.6). In general, the Ea values of phosphatases in soils were in the same order of magnitude as those of phosphatases in the waste materials studied.