Arylamidase activity in soils: effect of trace elements and relationships to soil properties and activities of amidohydrolases

The enzyme arylamidase (α-aminoacyl-peptide hydrolase, EC 3.4.11.2) catalyzes the hydrolysis of an N-terminal amino acid from peptides, amides or arylamides in soils. Recently, the activity of this enzyme was detected in soils, and a method was developed for its assay. The method was used in studies of the effects of salts of 25 trace elements on the activity of arylamidase in field-moist soils and their air-dried counterparts. At 5 μmol g−1 soil, the activity of arylamidase was inhibited in both air-dried and field-moist samples by 18 of the 25 trace elements used, and Ag(I), Hg(II) and Cd(II) were the most effective inhibitors (>55%). At this concentration, Co(II), Mg(II), Mn(II), B(III) and As(V) activated this enzyme in field-moist soils and their air-dried counterparts (1–49%), and W(VI) and Mo(VI) activated this enzyme in air-dried soils (4–21%), but inhibited it in the field-moist soils (7–46%). Arylamidase activity was significantly correlated with the content of organic C (r=0.80∗∗∗, P<0.001), total N (r=0.71∗∗∗), and clay (r=0.49∗∗, P<0.05), but not with sand or the pH of the 26 surface soils examined. The activity of this enzyme in soils was significantly correlated with the activities of l-asparaginase (r=0.91∗∗∗), l-aspartase (r=0.90∗∗∗), urease (r=0.87∗∗∗), and l-glutaminase (r=0.84∗∗∗) and with amidase (r=0.39∗).