Purification and characterization of extreme alkaline, thermostable keratinase, and keratin disulfide reductase produced by Bacillus halodurans PPKS-2

Two alkaline keratinases-I and II secreted by Bacillus halodurans PPKS-2 were purified and characterized. Both the keratinases were purified using ammonium sulfate, DEAE-Sephadex followed by Sephadex G-200 column chromatography. The purification was 21.5-fold and 11.17% yield for keratinase-I and 23.7-fold with yield 18.46 for keratinase-II and its molecular weights 30 and 66 kDa. Both purified enzymes were relatively stable over a broad pH range 7.0–13.0 and optimally active at pH 11.0 and 60–70 °C. Keratinase-II was found to be more stable at 70 °C for 3 h and retained 100% of its activity, whereas keratinase-I lost 10% activity. Keratinase-I had high keratin disulfide reductase activity with low keratinase activity whereas keratinase-II had high keratinase activity with low keratin disulfide reductase activity. Keratinase activities of both the enzymes were completely inhibited by PMSF at 1 mM, whereas keratin disulfide reductase activity of keratinase-I was not affected. Enzymes were active and stable in the presence of the surfactants, bleaching agents (20% H₂O₂), commercial detergents (1%), and SDS (20%). Both the enzymes were partially sequenced and found that keratinase-I and II had a homology with disulfide reductases and serine type of proteases, respectively.