CHARACTERIZATION OF FREE AND ADSORBED PHOSPHATASES IN SOILS

The kinetic and thermodynamic parameters of soil alkaline phosphatases, extracted humus-enzyme complexes, and water extracts were evaluated. The isolation procedure for humus-enzyme complexes involves exhaustive extraction of the soil with the chelating resin Chelex 100. The Km values for alkaline phosphatases in the resin extracts of two soils were 0.881 and 2.236 m M, respectively, and were greater than those of the water extracts (0.320 and 0.527 m M) and the soil suspensions (0.445 and 0.652 m M). The vmax values varied considerably, indicating the fundamental role of the enzyme concentration in the fractions and soils. The temperature of inactivation in the water extracts was 30°C, being 10° and 20°C lower than the temperature needed to inactivate alkaline phosphatase in humus-enzyme complexes and in soils, respectively. The results indicated that only a small portion of the enzyme activity was in a soluble state and that this fraction was characterized by a low thermal stability. The sorption of alkaline phosphatases to humic substances gives them additional thermal stability and leads to a partial inhibition of the enzyme. © 1990 Springer-Verlag.