Production and partial purification of an innovative heat resistant α-keratinase with some remarkable medical and industrial applications

Background and objectives
Keratinase has ultimate practical importance in industry, medicine, food industry and waste management fields. Their applications in wool and silk are as good cleaners and in leather industry as the best ever green dehairing agents providing high leather quality, as well they are used as crucial components of sophisticated detergents. Their medical prospective applications are in prion degradation and human callus removal. They convert keratinaceous wastes to valuable products saving the environment from hard keratin waste pollution. Bacteria, fungi and actinomycetes are effective keratinase producers and they are considered the most suitable sources. This study aims to formulate the production medium and to pinpoint the proper physiological conditions for the potent microorganism producing an efficient α-keratinase enzyme. The partial purification of the crude enzyme was successfully performed. The effect of the reaction temperature on both the crude and the partially purified enzyme (PPE) was duly studied with the thermostability of PPE. Some important applications have been implemented on PPE and these include leather dehairing, cloth stain removal, and topical treatment of human callus.
Materials and Methods
Thirteen recommended microbial strains were screened for effective and applicable α-keratinase productivity. Optimization of the cultural conditions for extracellular enzyme production and also the partial purification of the crude enzyme by ammonium sulphate salting out or by ethanol or acetone precipitation were carried out. The effect of reaction temperature on the enzyme and its thermostability were studied. Finally, the efficiency of the PPE on leather dehairing, stain removal, and human callus treatment was explored.
Results and conclusion
Among the 13 organisms screened, the fungal strain Trichoderma polysporum HZ-31 was the most potent producer of an influencial α-keratinase. The maximum α-keratinase activity of 58.2 UmL was obtained by the previous-mentioned strain after 5-days fermentation medium containing (%, w/v): whole chicken feathers 0.5, glucose 0.2, peptone 0.5, yeast extract 0.5, KHPO 0.1, KHPO 0.3, CaCl 0.1, MgSO 0.1, and pH 7.0. Acetone fractionation of the crude keratinase was the most proper and offered the most promising keratinase fraction PPE at 80–90% acetone. This fraction had high thermostability and was kept at 55°C for more than 98% of its original activity after 60 min heating and this temperature (55°C) was also the optimum for 2 h enzymatic reaction. Conclusively, the present study succeeded in the achievement of a constitutive extracellular alkaline α-keratinase, which successfully proceeded to complete leather unhairing after 12–16 h at 37°C, afforded high performance to cloth blood stain removal with Arial detergent after 2 h at 50°C and complete degradation of the human callus after 4 h at 50°C.