Premium
L‐Histidine Ammonia‐Lyase Activity in Soils
Author(s) -
Frankenberger W. T.,
Johanson J. B.
Publication year - 1982
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1982.03615995004600050012x
Subject(s) - histidine , chemistry , deamination , ammonia , soil water , toluene , enzyme , stereochemistry , organic chemistry , biology , ecology
Abstract Approximately 20 to 40% of the total nitrogen (N) in most surface soils is in the form of amino acids. Because of the importance of amino acids as a N source for plant and microbial growth, this work was carried out to study the enzyme that catalyzes the deamination of L‐histidine in soils. A simple, precise, and sensitive method to assay L‐histidine ammonia‐lyase (EC 4.3.1.3) activity in soils is described. This enzyme catalyzes the deamination of L‐histidine and produces urocanate and ammonia. The method involves determination by steam distillation of the ammonium (NH 4 + ) produced by L‐histidine NH 3 ‐lyase activity when soil is incubated with buffered (0.1 M Tris, pH 9.0) L‐histidine solution and toluene at 37°C for 48 h. Results show that the rate of NH 4 ‐N released through soil L‐histidine NH 3 ‐lyase activity exhibited a buffer pH optimum of 9.0. The reaction rate of this enzyme approached zero‐order kinetics when 50 m M of L‐histidine solution was added to soils. The D‐isomer of histidine was also deaminated in soils but was only 40% of the activity of the L‐isomer at saturating conditions of the substrate. The dependence of the reaction rate on the amount of enzyme present was linear up to 5 g of soil. Under the standard conditions, the accumulation of NH 4 ‐N was linear with time for at least 168 h. However, in the absence of toluene the NH 4 ‐N released with time followed an exponential relationship which might be due to induction of the enzyme by its substrate and a multienzyme system that degrades urocanate and its reaction products. The optimal temperature for soil L‐histidine NH 3 ‐lyase activity occurred at 80°C and denaturation began at 85°C. Among the various pretreatments that affected L‐histidine NH 3 ‐lyase activity in soils, 2‐mercaptoethanol, cysteine, CaCl 2 , and MgSO 4 activated this enzyme by an average of 12, 16, 11, and 11%, respectively. Treatments with formaldehyde, phenyl mercuric acetate, NaF, and NaAsO 2 inhibited the activity considerably.