Biochemical characterization of a surfactant-stable keratinase purified fromProteus vulgarisEMB-14 grown on low-cost feather meal

Objectives The bioaccumulation of keratinous wastes from poultry and dairy industries poses a danger of instability to the biosphere due to resistance to common proteolysis and as such, microbial- and enzyme-mediated biodegradation are discussed. Results In submerged fermentation medium,Proteus vulgarisEMB-14 utilized and efficiently degraded feather, fur and scales by secreting exogenous keratinase. The keratinase was purified 14-fold as a monomeric 49 kDa by DEAE-Sephadex A-50 anion exchange and Sephadex G-100 size-exclusion chromatography. It exhibited optimum activity at pH 9.0 and 60 degrees C and was alkaline thermostable (pH 7.0-11.0), retaining 87% of initial activity after 1 h pre-incubation at 60 degrees C. The K(m)and V(max)of the keratinase with keratin azure were respectively 0.283 mg/mL and 0.241 U/mL/min. Activity ofP. vulgariskeratinase was stimulated by Ca2+, Mg2+, Zn2+, Na(+)and maintained in the presence of some denaturing agents, except beta-mercaptoethanol while Cu(2+)and Pb(2+)showed competitive and non-competitive inhibition with K(i)6.5 mM and 17.5 mM, respectively. Conclusion This purifiedP. vulgariskeratinase could be surveyed for the biotechnological transformation of bioorganic keratinous wastes into valuable products such as soluble peptides, cosmetics and biodegradable thermoplastics.