Keratinase

Keratinases are proteolytic enzymes in nature. They were classified as proteinases of unknown mechanism as recommended by the Nomenculture Committee on the International Union of Biochemistry (1978) with EC number 3.4.99 (Owen et al., 1983). Recently, some researchers defined keratinase as a serine protease due to its 97% sequence homology with alkaline protease, and it is also inhibited by the same inhibitor that inhibits serine protease (Wang et al., 1995; Taha et al., 1998 and Bressollier et a1., 1999).

Keratinases are produced only in the presence of keratin-containing substrate. They mainly attack the disulfide (-S-S-) bond of the keratin substrate (Bockel et al., 1995). Keratinase production in various microorganisms was reported on by a number of researchers. It was found that keratinase in fungi, Streptomyces and bacteria were produced in nearly at alkaline pH and almost thermophilic temperatures. These enzymes have a wide range of substrate specificity such as it can degrade other fibrous protein fibrin, elastin, collagen and other non fibrous protein like casein, bovine serum albumin gelatin etc. (Noval et al., 1959; Mukhapadhayay et al., 1989; Dozie et al., 1994; Lin et al., 1995; Letourneau et al., 1998; and Bressollier et al., 1999).

At first Molyneux et al. (1959) attempted to isolate some bacteria that are able to degrade keratin. He isolated organism from the contents of experimentally induced dermoid cysts from mid lateral region of sheep. Examination of wool sample showed degraded wool with numerous corticle and cyticular cells. He found disruption of wool fiber in both in vivo and in vitro. He showed that the organisms belong to genus Bacillus and the organism was capable of attacking native wool protein. The same year Noval et al. (1959) published another article on enzymatic decomposition of native keratin by Streptomyces fradiae. They showed extracellular enzyme secreted by these bacteria capable of degrading the human hair in its native state.

Keratinolytic protein from keratinophilic fungi were reported by Yu et al. (1968), Asahi et al. (1985), and Willams et al. (1989). Mukhopadhay et al. (1989) reported keratinase production by Streptomyces sp. He isolated an inducible extracellular homogenous enzyme, which shows a 7.5-fold increases in its activity after DEAE cellulose column chromatography. The enzyme-activity was inhibited by reduced glutathione, PMSF and 2-¬Mercaptaethanol.

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