Michaelis Constants of Urease in Soils and Soil Fractions

Abstract

AbstractStudies to determine the Michaelis constant (Km value) for urease activity in Iowa surface soils showed that the value obtained for the activity of this enzyme was different for different soils. When the method used to determine Km did not involve shaking of the soil‐substrate mixtures, the Km value for urease activity ranged from 1.3 × 10‐3M to 7.0 × 10‐3M. Shaking the soil‐substrate mixtures during incubation decreased the Km value obtained, and statistical analysis showed that this value was significantly correlated with organic C and total N. There was no significant correlation, however, between Km value of the urease activity and other soil properties studied (pH, percentage clay, percentage silt, percentage sand). The maximum enzyme reaction velocity (Vmax value) for urease activity in soils was markedly different for different soils and always increased when the soil‐substrate mixtures were shaken during incubation. The Vmax values obtained from static and shaking incubation techniques were significantly correlated with organic C, total N, and clay content.Results reported show that the Km value of urease in soils is similar to that of urease in soil fractions and is nearly two orders of magnitude lower than the previously reported Km value for this enzyme in soils.