Estimation of L-glutaminase and L-asparaginase activities in soils by the indophenol method

Abstract

Abstract A simple and rapid method was developed for determining L-glutaminase and L-asparaginase activities in soils. It involved colorimetric estimation of NH4 + released by the activity of L-glutaminase and L-asparaginase when soil was incubated with 0.25 M L-glutamine or L-asparagine in 0.1 M phosphate buffer (pH 7.6) and toluene used as a germicide. The indophenol method was applied to the assay of NH4 + for soil L-glutaminase and L-asparaginase activities. Color development in the indophenol method required one hour. The color development was stable for 2 d and was not appreciably affected by the presence of L-glutamine, L-glutamic acid, L-asparagine, and L-aspartic acid. In addition, no turbidity nor precipitate appeared in the presence of a high concentration (10 μg) of NH4 +-N. The L-glutaminase activity was estimated in three soil samples differing in pH, organic-C content, and land use. The L-glutaminase activity in the three soils ranged from 28 to 1,470 mU (10-9 mol min-1 g-1 of dry soil at 3...