The fungus Scopulariopsis brevicaulis was isolated from poultry farm soil at Namakkal, India. The extracellular keratinase from this fungus was purified to homogeneity by ammonium sulphate precipitation and procedure involving DEAE-Cellulose and Sephadex G-100 chromatographic techniques. The purified enzyme was formed from a monomeric protein with molecular masses of 39 and 36kDa by SDS-PAGE and gel filtration, respectively. The optimum pH at 40 degrees C was 8.0 and the optimum temperature at pH 8.0 was 40 degrees C. The activity of purified keratinase with respect to pH, temperature and salt concentration was optimized by Box-Behnken design experiment. It was shown that a second-order polynominal regression model could properly interpret the experimental data with an R-2-value of 0.9957 and an F-value of 178.32, based on the maximum enzyme activity examined. Calculated optimum conditions were predicted to confer a 100% yield of keratinase activity with 5 mM CaCl2, pH 8.0 and at a temperature of 40 degrees C. The enzyme was strongly inhibited by PMSF, which suggests a serine residue at or near an active site. The purified keratinase was examined with its potential for dehairing the skin. (c) 2004 Elsevier Inc. All rights reserved.