A novel keratinase from Chryseobacterium sp. strain kr6 was purified to homogeneity by (NH4)(2)SO4 precipitation, gel permeation on Sephadex G-100, and Q-Sepharose Fast Flow anion-exchange chromatography. The molecular weight of the purified enzyme was around 20 kDa. Kinetic and thermodynamic parameters for thermal inactivation were determined. The influence of Ca2+ and Mg2+ ions and purification degree on the enzyme stability was evaluated in the range of 50 to 60 A degrees C. The results showed that first-order kinetics explained well the thermal denaturation of the keratinase in this temperature interval. The presence of Ca2+ increases significantly the enzyme stability. Compared with the controls, the half-life of the purified enzyme after two purification steps in the presence of Ca2+ increased 7.3, 20.2, and 9.8 fold at 50, 55, and 60 A degrees C, respectively. Thermodynamics parameters for thermal inactivation were also determined.