Purification, characterization, and antimicrobial activity of nontoxic trypsin inhibitor from Albizia amara Boiv.

• A novel, nontoxic, proteinaceous trypsin inhibitor was reported from seeds of Albizia amara.
• The purified proteinaceous protease inhibitor (API) is a thermo- and salt-stable 49-kDa protein.
• API has antifungal activity against Alternaria alternata, Alternaria tenuissima, and Candida albicans.
• API has antibacterial activity against Pseudomonas aeruginosa and Bacillus subtilis.
• API has potential to inhibit trypsin, chymotrypsin, and proteinase-K.

The present investigation describes the purification, and characterization of a novel, thermostable, nontoxic, proteinaceous trypsin inhibitor extracted from seeds of Albizia amara Boiv. The proteinaceous protease inhibitor (API) was purified via acetone fractionation, ion-exchange chromatography (diethylaminoethyl (DEAE) cellulose), and gel permeation chromatography (GPC; Sephadex G-100). The apparent molecular weight of the API is 49 kDa and is identified as a serine protease inhibitor. The API remains active in a wide pH range (3.0–8.0), and showed thermal stability at 60 °C. The API inhibits trypsin by a mixed inhibitory mechanism with an inhibition constant (Ki) of 1.24 × 10−8 M using BApNA (Nα-benzoyl-dl-arginine-p-nitroanilide hydrochloride) as the substrate. The API also showed substantial activity in the presence of several metal ions, surfactant (Triton X-100), oxidizing agent (dimethyl sulfoxide; DMSO), and NaCl (5%). Moreover, API retained 85% trypsin inhibition activity upon storage at 4 °C over a period of 6 months. The antimicrobial effectiveness of the API against Pseudomonas aeruginosa, Bacillus subtilis, Alternaria alternata, Alternaria tenuissima, and Candida albicans reported in this study suggests its utility as a potential antimicrobial component.

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