Characterization of a Proteinase Inhibitor from Cajanus cajan (L.)
- Cite this article as:
- Haq, S.K. & Khan, R.H. J Protein Chem (2003) 22: 543. doi:10.1023/B:JOPC.0000005504.57372.5b
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A protein proteinase inhibitor (PI) has been purified from pigeonpea Cajanus cajan (L.) PUSA 33 variety by acetic-acid precipitation, salt fractionation and chromatography on a DEAE-Cellulose column. The content of inhibitor was found to be 15 mg/20 g dry weight of pulse. The molecular weight of the inhibitor as determined by SDS-PAGE under reducing conditions was found to be about 14,000. It showed inhibitory activity toward proteolytic enzymes belonging to the serine protease group, namely trypsin and α-chymotrypsin. The inhibitory activity was stable over a wide range of pH and temperatures. Estimation of sulfhydryl groups yielded one free cysteine and at least two disulfide linkages. N-terminal sequence homology suggests that it belongs to the Kunitz inhibitor family. Structural analysis by circular dichroism shows that the inhibitor possesses a largely disordered structure.