Comparative Assessment of Trypsin Inhibitor vis-à-vis Kunitz Trypsin Inhibitor and Bowman-Birk Inhibitor Activities in Soybean

Abstract

Trypsin inhibitor activity (TIA) in soybean is attributed to two polypeptides, namely, Kunitz trypsin inhibitor (KTI) and Bowman-Birk inhibitor (BBI). Standard spectrophotometric protocol widely followed for estimation of TIA is cumbersome and does not distinguish KTI from BBI. In the present investigation, extraction conditions for KTI were optimized and different forms of this polypeptide were resolved in 180 soybean genotypes of Indian and exotic origin through native PAGE. This led to the identification of three KTI alleles, namely, Tia, Tib, and Tic, with Tia occurring in most of the Indian genotypes. Trypsin-KTI complex assay exhibited binding of Tia polypeptide with 2.51 fold concentration of trypsin. Subsequently, seeds of selected genotypes were subjected to estimation of KTI and BBI activity through densitometry and enzyme-linked immunosorbent assay (ELISA), respectively; and total TIA through standard spectrophotometric protocol. Summation of KTI and BBI was significantly (P < 0.05) lower than that of TIA determined through the spectrophotometric method.