A method for estimation of l-glutaminase activity in soils

Abstract

A method was devised for the rapid and simple assay of L-glutaminase activity in soils. It involved colorimetric estimation of NH4+ released by L-glutaminase activity when soil was incubated with 0.25 M L-glutamine in 0.1 M phosphate buffer (pH 7.6) and toluene was used as a germicide. The released NH4+ was extracted with 0.5 M KCI. For the estimation of NH4+, the improved Nessler's method was adopted to assay for soil l-glutaminase activity. The filtrate was suitably diluted with distilled water in order to lower the concentration of the turbidity-forming substance in soil extract. Addition of phosphate buffer prevented the color-developed solution to become turbid. To the diluted filtrate was added 0.1 M phosphate buffer (pH 7.6) and Nessler's reagent respectively. The color intensity of the complex formed was determined by absorbancy. The L-glutaminase activity was estimated on five soil samples different in pH, organic-C content and vegetation. The L-glutaminase activity in five soils ranged from 36 to 633 milli-unit (nmol per min per gram of dry soil at 30°C). The optimum pH of L-glutaminase activity in soils was about 7.6 in phosphate buffer. © 1983 Taylor & Francis Group, LLC.