Michaelis Constants of Urease in Soils and Soil Fractions
1973
Tabatabai, M. A.
Studies 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.
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