Parameter estimation for models of ligninolytic and cellulolytic enzyme kinetics

While soil enzymes have been explicitly included in the soil organic carbon (SOC) decomposition models, there is a serious lack of suitable data for model parameterization. This study provides well-documented enzymatic parameters for application in enzyme-driven SOC decomposition models from a compilation and analysis of published measurements. In particular, we developed appropriate kinetic parameters for five typical ligninolytic and cellulolytic enzymes (beta-glucosidase, cellobiohydrolase, endo-glucanase, peroxidase, and phenol oxidase). The kinetic parameters included the maximum specific enzyme activity (V-max) and half-saturation constant (K-m) in the Michaelis-Menten equation. The activation energy (Ea) and the pH optimum and sensitivity (pH(opt) and pH(sen)) were also analyzed. pH(sen) was estimated by fitting an exponential-quadratic function. The V-max values, often presented in different units under various measurement conditions, were converted into the same units at a reference temperature (20 degrees C) and pH(opt). Major conclusions are: (i) Both V-max and K-m were log-normal distributed, with no significant difference in V-max exhibited between enzymes originating from bacteria or fungi. (ii) No significant difference in V-max was found between cellulases and ligninases; however, there was significant difference in K-m between them. (iii) Ligninases had higher Ea values and lower pH(opt) than cellulases; average ratio of PHsen to pH(opt) ranged 0.3-0.4 for the five enzymes, which means that an increase or decrease of 1.1-1.7 pH units from pH(opt) would reduce V-max by 50%. (iv) Our analysis indicated that the V-max values from lab measurements with purified enzymes were 1-2 orders of magnitude higher than those for use in SOC decomposition models under field conditions. (C) 2012 Elsevier Ltd. All rights reserved.