Modeling cellobiose hydrolysis with integrated kinetic models

The enzyme cellobiase Novozym 188, which is used for improving hydrolysis o f bagasse with cellulase, was characterized in its commercial available for m and integrated kinetic models were applied to the hydrolysis of cellobios e. The specific activity of this enzyme was determined for pH values from 3 .0-7.0, and temperatures from 40-75 degrees C, with cellobiose at 2 g/L. Th ermal stability was measured at pH 4.8 and temperatures from 40-70 degrees C. Substrate inhibition was studied at the same pH, 50 degrees C, and cello biose concentrations from 0.4-20 g/L. Product inhibition was determined at 50 degrees C, pH 4.8, cellobiose concentrations of 2 and 20 g/L, and initia l glucose concentration nearly zero or 1.8 g/L. The enzyme has shown the gr eatest specific activity, 17.8 U/mg, at pH 4.5 and 65 degrees C. Thermal ac tivation of the enzyme followed Arrhenius equation with the Energy of Activ ation being equal to 11 kcal/mol for pH values 4 and 5. Thermal deactivatio n was adequately modeled by the exponential decay model with Energy of Deac tivation giving 81.6 kcal/mol. Kinetics parameters for substrate uncompetit ive inhibition were: Km = 2.42 mM, V-max = 16.31 U/mg, Ks = 54.2 mM. Substr ate inhibition was clearly observed above 10 mM cellobiose. Product inhibit ion at the concentration studied has usually doubled the time necessary to reach the same conversion at the lower temperature tested.