Subtilisin is a non-specific protease initially obtained from Bacillus subtilis. Subtilisins belong to subtilases, a group of serine proteases that initiate the nucleophilic attack on the peptide (amide) bond through a serine residue at the active site. Subtilisins typically have molecular weights of about 20,000 to 45,000 dalton. They can be obtained from certain types of soil bacteria, for example, Bacillus amyloliquefaciens from which they are secreted in large amounts. The structure of subtilisin has been determined by X-ray crystallography. It is a 275-residue globular protein with several alpha-helices, and a large beta-sheet. It is structurally unrelated to the chymotrypsin-clan of serine proteases, but uses the same type of catalytic triad in the active site. This makes it a classic example of convergent evolution. Subtilisins are widely used in commercial products and the native enzyme is easily inactivated by bleach and also called stain cutter.
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