| Abstract: | An ongoing challenge in enzymology is the differentiation between the various pools of enzymes in soils, i.e. between accumulated (extracellular) enzymes and enzymes associated with the microbial biomass (intracellular enzymes). In order to solve this problem, 10 surface soils representing a wide range of physico‐chemical properties and purified reference enzyme proteins were fumigated for 24 h at 25 °C. The activities of L‐asparaginase, L‐glutaminase, amidase, and L‐aspartase were assayed in chloroform fumigated soils, in reference enzyme proteins and in their nonfumigated counterparts in the presence and absence of toluene. Chloroform fumigation decreased the activities of L‐asparaginase, L‐glutaminase, and L‐aspartase in soils, on average, by 41, 78, and 78 %, respectively. The response of amidase activity towards chloroform fumigation of soils varied within the 10 soils studied. In five soils increases in activity values up to 40 % were observed. A loss of amidase activity, varying between 7 and 17 %, was found in four soils, whereas in one soil no effect of chloroform fumigation was determined. Enzyme activities of the four purified reference proteins were decreased by fumigation, with L‐glutaminase showing a nearly complete inhibition of 99 %, followed by amidase, L‐aspartase, and L‐asparaginase with an inhibition of 29, 18, and 7 %, respectively. Toluene treatment of the nonfumigated soils resulted in increases in the activity values of L‐asparaginase, L‐glutaminase, and L‐aspartase of 21 to 213 % (average of 10 soils). In contrast, amidase activity of soils was decreased in the presence of toluene by a mean of 32 %. Enzyme protein concentrations, calculated for the 10 soils, based on the specific activities of the purified enzymes (i.e., activity values per mg protein) and the activity values obtained in the soils, were, on average, 0.73, 0.50, 3.38, and 2.61 mg protein (kg soil)—1 for L‐asparaginase, L‐glutaminase, amidase, and L‐aspartase, respectively. Comparison of activity values of soil amidohydrolases with the protein concentrations present in soils indicates that catalytic efficiency can vary greatly among different soil enzymes. |
