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Kinetic Properties of L-Histidine Ammonia-Lyase Activity in Soils¹

ABSTRACT

Enzyme kinetic analyses were performed to characterize the L-histidine ammonia-lyase-catalyzed reaction in soils. The velocity curves of soil L-histidine NH₃-lyase as a function of substrate concentration displayed sigmoidicity. The apparent [S]_0.5 values of this enzyme in eight soils ranged from 26 to 41 mM (avg = 32 mM) and the apparent V_max values ranged from 51 to 97 µg NH₄-N released·g of soil^–1·48 h^–1. The velocity of this enzyme was described by the Hill equation which measures the deviation in hyperbolicity of saturation curves. The experimental data yields strong cooperativity in terms of the Hill coefficient (n_app = 4.0 to 5.5) and shape of sigmoidicity ([S]_0.9/[S]_0.1 = 2.2 to 3.0). The E_a (activation energies) and Q₁₀ values for the L-histidine NH₃-lyase catalyzed reaction in seven soils at temperatures below inactivation (< 60 °C) ranged from 37.0 to 65.4 kJ/mol and 1.51 to 2.58, respectively.

¹ Contribution from the Dep. of Soil and Environ. Sci., Univ. of California, Riverside, CA 92521.

² Assistant Professor, Univ. of California, Riverside.

Received for publication November 19, 1981. Accepted for publication September 9, 1982.