2Institute for Nanobiomedical Technology and Membrane Biology, Sichuan University, Chengdu 610064, China; fax: +86-28-8541-5300; E-mail: firstname.lastname@example.org
* To whom correspondence should be addressed.
Received September 25, 2007; Revision received February 26, 2008
The trypsin inhibitor SOTI was isolated from Spinacia oleracea L. seeds through ammonium sulfate precipitation, Sepharose 4B-trypsin affinity chromatography, and Sephadex G-75 chromatography. This typical Kunitz inhibitor showed remarkable stability to heat, pH, and denaturant. It retained 80% of its activity against trypsin after boiling for 20 min, and more than 90% activity when treated with 6 M guanidine hydrochloride. The formation of stable SOTI–trypsin complex (Ki = 2.3·10–6 M) is consistent with significant inhibitory activity of SOTI against trypsin-like proteinases present in the larval midgut of Pieris rapae. Sequences of SOTI fragments showed homology with other inhibitors.
KEY WORDS: Spinacia oleracea L., trypsin inhibitor, protein stability, Kunitz family, Pieris rapae