Acta Biologica Indica 2014, 3(1):522-526 522 Identification of plant extracts expressing trypsin inhibitor C. Divya 1 , K. Sreejina Sreedharan 1 , Bindu Punathum Parambath 2 , Kannan Vadakkadath Meethal 1 1 Department of Zoology, University of Calicut, Thenjipalam, Kerala, 673635, India, kannanvm@yahoo.com; 2 Department of Statistics, T.M. Government College, Tirur, Kerala, India ABSTRACT Plant protease inhibitors (PPIs) are compounds which play a potent defensive role against pest and pathogens, thereby protecting the plants. In this work we tested different plant extracts to identify extracts containing inhibitor against trypsin activity. Plant extracts were made by homogenizing soaked leaves/seeds/root modification of plants in bicarbonate buffer, pH 9.0.The homogenates were centrifuged at 10,000 rpm at 4°C for 10 minutes. The supernatant containing the soluble proteins were used for protease inhibition assay. Protease inhibition assay was carried out in a total volume of 1 ml containing 67 µl trypsin (Bovine), 25 µl plant extract, 511 µl Tris buffer, 67µl NaCl and 330 µg Nα-Benzoyl-DL-Arginine-P-Nitro Anilide (BAPNA) as substrate. On screening 19 extracts from different plants, we found 9 of them inhibited trypsin activity greater than 40%. The percentage inhibition of these plants are Garcinia xanthochymus (96.7± 0.4 %), Datura stramonium (86.1±1.6%), Ricinus communis (74.05±0.45%), Phyllanthus amarus (72.05±2.15%), Santalum album (64.4±1.7 %), Plectranthus ambonicus (62.15±2.45% ), Croton hirtus ( 55.85±0.9% ), Zea mays (48±2.1% ) and Prunus cerasifera (45.38±0.125%). Of these, to our knowledge no trypsin inhibitor was reported from Garcinia xanthochymus, Datura stramonium, Plectranthus ambonicus, Prunus cerasifera, Phyllanthus amarus, Santalum album, and Croton hirtus. As trypsin is a serine protease, a predominant class of protease in the gut of lepidopteran larvae, this screening will be useful to identify extract containing protease inhibitor against the gut protease of lepidopteran pests. Protease inhibitors from these extracts can be exploited for control of lepidopteran pests. Keywords: trypsin, proteases, plant protease inhibitors, Garcinia xanthochymus, Datura stramonium INTRODUCTION Protease inhibitors (PIs) are molecules that inhibit the function of proteases. Many naturally occurring PIs are proteins. In seeds and tubercles about 10% of their total protein is represented by protease inhibitors [1-3]. These plant protease inhibitors (PPIs) play essential roles in biological systems such as regulating proteolytic processes, and participate in defence mechanisms against attack by insects, fungi, and other pathogenic microorganisms. Plant protease inhibitors were first reported more than 65 years ago. Soybean trypsin inhibiter was crystallised by Kunitz in 1947 [4]. This inhibiter was the main tool for studies that helped to understand the mechanism of PI interaction for the majority of serine proteases. The PIs binds to the active site on the enzyme to form a complex with a very low dissociation constant. A binding loop on the inhibitor, usually “locked” into conformation by a disulphide bond, projects from the surface of the molecule and contains a peptide bond which can be cleaved by the enzyme [5,6]. This peptide Research Article, Acta Biologica Indica 2014, 3(1):522-526 © 2014 Association for the Advancement of Biodiversity Science pISSN 2319-1244, eISSN 2279-0160