Kinetic Properties of L-Histidine Ammonia-Lyase Activity in Soils1
- W. T. Frankenberger2
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 Vmax 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 (napp = 4.0 to 5.5) and shape of sigmoidicity ([S]0.9/[S]0.1 = 2.2 to 3.0). The Ea (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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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