Gangsheng Wang, Wilfred M. Post, Melanie A. Mayes, Joshua T. Frerichs, Jagadamma Sindhu
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
While soil enzymes have been explicitly included in the soil organic carbon (SOC) ecomposition models,there is a serious lack of suitable data for model parameterization. This study provides well-documentedenzymatic parameters for application in enzyme-driven SOC decomposition models from a compilationand analysis of published measurements. In particular, we developed appropriate kinetic parameters forfive typical ligninolytic and cellulolytic enzymes (b-glucosidase, cellobiohydrolase, endo-glucanase,peroxidase, and phenol oxidase). The kinetic parameters included the maximum specific enzymeactivity (Vmax) and half-saturation constant (Km) in the MichaeliseMenten equation. The activationenergy (Ea) and the pH optimum and sensitivity (pHopt and pHsen) were also analyzed. pHsen wasestimated by fitting an exponential-quadratic function. The Vmax values, often presented in differentunits under various measurement conditions, were converted into the same units at a referencetemperature (20 _C) and pHopt. Major conclusions are: (i) Both Vmax and Km were log-normal distributed, with no significant difference in Vmax exhibited between enzymes originating from bacteria or fungi.(ii) No significant difference in Vmax was found between cellulases and ligninases; however, there wassignificant difference in Km between them. (iii) Ligninases had higher Ea values and lower pHopt thancellulases; average ratio of pHsen to pHopt ranged 0.3e0.4 for the five enzymes, which means that anincrease or decrease of 1.1e1.7 pH units from pHopt would reduce Vmax by 50%. (iv) Our analysis indicatedthat the Vmax values from lab measurements with purified enzymes were 1e2 orders of magnitudehigher than those for use in SOC decomposition models under field conditions.