Aspartase activity in soils: effects of trace elements and relationships to other amidohydrolases

The enzyme aspartase (L-aspartase ammonia-lyase, EC 4.3.1.1) catalyzes the hydrolysis of L-aspartate to produce fumarate and NH3. This enzyme is invol ved in N mineralization in soils. Recently, the activity of this enzyme was detected in soils, and a method was developed for its assay. The method wa s used in studies of the effects of the salts of 24 trace elements on the a ctivity of aspartase in three field-moist soils and their air-dried counter parts. At 5 mu mol g(-1) soil, all the trace elements inhibited aspartase a ctivity in the soils. With most of the elements, greater inhibition was fou nd in air-dried than in field-moist soils. Among the trace elements studied , Ag(I) and Hg(II) were the most effective inhibitors of aspartase activity ; >85% when added at 5 mu mol g(-1) soil. The least inhibition (12%) was wi th Ni added to the field-moist Harps soil and the greatest (98%) was with A g(I) in the air-dried Weller soil. Aspartase activity was significantly cor related with the contents of organic C (r = 0.85*** P < 0.001), total N (r = 0.73***) and clay (r = 0.44*, P < 0.05) but not with the content of sand or the pH of 27 surface soils examined, including the three soils used in t he studies of the effects of trace elements. The activity of this enzyme in soils was significantly correlated with the activities of asparaginase (I = 0.94***), glutaminase (r = 0.88***), urease (r = 0.80***) and amidase (I = 0.44*). (C) 1998 Elsevier Science Ltd. All rights reserved.