FACTORS AFFECTING L-ASPARAGINASE ACTIVITY IN SOILS

Studies on the distribution of L-asparaginase in soil profile samples revealed that its activity generally decreases with sample depth and is accompanied by a decrease in organic C content. Statistical analyses indicated that L-asparaginase activity was significantly correlated (**P < 0.01) with organic C (r = 0.86**) and total N (r = 0.78**) in the 26 surface soil samples examined. There was no significant relationship between L-asparaginase activity and the percentage of clay or sand. There was, however, a significant correlation between L-asparaginase activity and amidase (r = 0.82**) and urease (r = 0.79**) activities in the surface samples studied. The effects of 21 trace elements, 12 herbicides, 2 fungicides, and 2 insecticides on L-asparaginase activity in soils showed that most of the trace elements and pesticides, at the concentrations used, inhibited the reaction catalyzed by this enzyme. The degree of inhibition varied among soils. When the trace elements were compared, at the rate of 5-mu-mol g-1 soil, the average inhibition of L-asparaginase in three soils showed that Ag(I), Cd(II), Hg(II), Ni(II), Pb(II), and V(IV) were the most effective inhibitors (average inhibition less-than-or-equal-to 20%). The least effective inhibitors (average less-than-or-equal-to 10%) included Cu(I), Ba(II), Co(II), Sn(II), Zn(II), Al(III), Se(IV), As(V), and Mo(VI). Other trace elements that inhibited L-asparaginase activity in soils were Cu(II), Mn(II), As(III), B(III), Cr(III), Fe(III), Ti(IV), and W(VI). When the pesticides were compared, at the rate of 10-mu-g active ingredient g-1 soil, the average inhibition of L-asparaginase activity in three soils ranged from 4% with Merpan to 46% with Malaspray. Other pesticides that inhibited L-asparaginase activity in soils (average inhibition in parentheses) were Aatrex (17%), Alanap (21%), amiben (18%), Banvel (12%), Bladex (24%), 2,4-D (17%), Dinitramine (19%), Eradicane (16%), Lasso (40%), Paraquat (33%), Sutan (39%), Treflan (7%), Menesan (18%), and Diazinon (33%).